title: De Stijl

text: The name "Nieuwe Beelding" was a term first coined in 1917 by Mondrian, who wrote a series of twelve articles called "De Nieuwe Beelding in de schilderkunst" ("Neo-Plasticism in Painting") that were published in the journal "De Stijl". In 1920 he published a book titled "Le Néo-Plasticisme".


title: De Stijl

text: Around 1921, the group's character started to change. From the time of van Doesburg's association with Bauhaus, other influences started playing a role. These influences were mainly Malevich and Russian Constructivism, to which not all members agreed. In 1924 Mondrian broke with the group after van Doesburg proposed the theory of elementarism, suggesting that a diagonal line is more vital than horizontal and vertical ones. In addition, the De Stijl group acquired many new "members". Dadaist influences, such as I. K. Bonset's poetry and Aldo Camini's "antiphilosophy" generated controversy as well. Only after Van Doesburg's death was it revealed that Bonset and Camini were two of his pseudonyms.


title: De Stijl

text: Because of van Doesburg's pivotal role within De Stijl, the group did not survive. Individual members remained in contact, but De Stijl could not exist without a strong central character. Thus, it may be wrong to think of De Stijl as a close-knit group of artists. The members knew each other, but most communication took place by letter. For example, Mondrian and Rietveld never met in person.


title: De Stijl

text: Many, though not all, artists did stay true to the movement's basic ideas, even after 1931. Rietveld, for instance, continued designing furniture according to De Stijl principles, while Mondrian continued working in the style he had initiated around 1920. Van der Leck, on the other hand, went back to figurative compositions after his departure from the group.


title: De Stijl

text: The De Stijl influence on architecture remained considerable long after its inception; Mies van der Rohe was among the most important proponents of its ideas. Between 1923 and 1924, Rietveld designed the Rietveld Schröder House, the only building to have been created completely according to De Stijl principles. Examples of Stijl-influenced works by J.J.P. Oud can be found in Rotterdam ("") and Hook of Holland. Other examples include the Eames House by Charles and Ray Eames, and the interior decoration for the Aubette dance hall in Strasbourg, designed by Sophie Taeuber-Arp, Jean Arp and van Doesburg.


title: De Stijl

text: Works by De Stijl members are scattered all over the world, but De Stijl-themed exhibitions are organised regularly. Museums with large De Stijl collections include the Gemeentemuseum in The Hague (which owns the world's most extensive, although not exclusively De Stijl-related, Mondrian collection) and Amsterdam's Stedelijk Museum, where many works by Rietveld and Van Doesburg are on display. The Museum of Utrecht has the largest Rietveld collection worldwide; it also owns the Rietveld Schröder House, Rietveld's adjacent "show house", and the Rietveld Schröder Archives.


title: De Stijl

text: The movement inspired the design aesthetics of Rumyantsevo and Salaryevo stations of Moscow Metro opened in 2016.


title: Pumped-storage hydroelectricity

text: Pumped-storage hydroelectricity (PSH), or pumped hydroelectric energy storage (PHES), is a type of hydroelectric energy storage used by electric power systems for load balancing. The method stores energy in the form of gravitational potential energy of water, pumped from a lower elevation reservoir to a higher elevation. Low-cost surplus off-peak electric power is typically used to run the pumps. During periods of high electrical demand, the stored water is released through turbines to produce electric power. Although the losses of the pumping process make the plant a net consumer of energy overall, the system increases revenue by selling more electricity during periods of peak demand, when electricity prices are highest. If the upper lake collects significant rainfall or is fed by a river then the plant may be a net energy producer in the manner of a traditional hydroelectric plant.


title: Pumped-storage hydroelectricity

text: Pumped-storage hydroelectricity allows energy from intermittent sources (such as solar, wind) and other renewables, or excess electricity from continuous base-load sources (such as coal or nuclear) to be saved for periods of higher demand. The reservoirs used with pumped storage are quite small when compared to conventional hydroelectric dams of similar power capacity, and generating periods are often less than half a day.


title: Pumped-storage hydroelectricity

text: Pumped storage is by far the largest-capacity form of grid energy storage available, and, as of 2020, the United States Department of Energy Global Energy Storage Database reports that PSH accounts for around 95% of all active tracked storage installations worldwide, with a total installed throughput capacity of over 181 GW, of which about 29 GW are in the United States, and a total installed storage capacity of over 1.6 TWh, of which about 250 GWh are in the United States. The "round-trip" energy efficiency of PSH varies between 70%–80%, with some sources claiming up to 87%. The main disadvantage of PSH is the specialist nature of the site required, needing both geographical height and water availability. Suitable sites are therefore likely to be in hilly or mountainous regions, and potentially in areas of natural beauty, making PSH susceptible to social and ecological issues. Many recently proposed projects, at least in the U.S., avoid highly sensitive or scenic areas, and some propose to take advantage of "brownfield" locations such as disused mines.


title: Pumped-storage hydroelectricity

text: At times of low electrical demand, excess generation capacity is used to pump water into the upper reservoir. When there is higher demand, water is released back into the lower reservoir through a turbine, generating electricity. Reversible turbine/generator assemblies act as a combined pump and turbine generator unit (usually a Francis turbine design). Variable speed operation further optimize the round trip efficiency in pumped hydro storage plants.


title: Pumped-storage hydroelectricity

text: In micro-PSH applications, a group of pumps and Pump As Turbine (PAT) could be implemented respectively for pumping and generating phases. The same pump could be used in both modes by changing rotational direction and speed: the operation point in pumping usually differs from the operation point in PAT mode.


title: Pumped-storage hydroelectricity

text: In open-loop systems, pure pumped-storage plants store water in an upper reservoir with no natural inflows, while pump-back plants utilize a combination of pumped storage and conventional hydroelectric plants with an upper reservoir that is replenished in part by natural inflows from a stream or river. Plants that do not use pumped-storage are referred to as conventional hydroelectric plants; conventional hydroelectric plants that have significant storage capacity may be able to play a similar role in the electrical grid as pumped storage by deferring output until needed.


title: Pumped-storage hydroelectricity

text: Taking into account evaporation losses from the exposed water surface and conversion losses, energy recovery of 70–80% or more can be achieved. This technique is currently the most cost-effective means of storing large amounts of electrical energy, but capital costs and the presence of appropriate geography are critical decision factors in selecting pumped-storage plant sites.


title: Pumped-storage hydroelectricity

text: The relatively low energy density of pumped storage systems requires either large flows and/or large differences in height between reservoirs. The only way to store a significant amount of energy is by having a large body of water located relatively near, but as high above as possible, a second body of water. In some places this occurs naturally, in others one or both bodies of water were man-made. Projects in which both reservoirs are artificial and in which no natural inflows are involved with either reservoir are referred to as "closed loop" systems.


title: Pumped-storage hydroelectricity

text: These systems may be economical because they flatten out load variations on the power grid, permitting thermal power stations such as coal-fired plants and nuclear power plants that provide base-load electricity to continue operating at peak efficiency, while reducing the need for "peaking" power plants that use the same fuels as many base-load thermal plants, gas and oil, but have been designed for flexibility rather than maximal efficiency. Hence pumped storage systems are crucial when coordinating large groups of heterogeneous generators. Capital costs for pumped-storage plants are relatively high, although this is somewhat mitigated by their proven long service life of decades - and in some cases over a century, which is three to five times longer than utility-scale batteries. When Electricity prices become negative, pumped hydro operators may earn twice - when "buying" the electricity to pump the water to the upper reservoir at negative spot prices and again when selling the electricity at a later time when prices are high.


title: Pumped-storage hydroelectricity

text: Along with energy management, pumped storage systems help control electrical network frequency and provide reserve generation. Thermal plants are much less able to respond to sudden changes in electrical demand, potentially causing frequency and voltage instability. Pumped storage plants, like other hydroelectric plants, can respond to load changes within seconds.


title: Pumped-storage hydroelectricity

text: The most important use for pumped storage has traditionally been to balance baseload powerplants, but may also be used to abate the fluctuating output of intermittent energy sources. Pumped storage provides a load at times of high electricity output and low electricity demand, enabling additional system peak capacity. In certain jurisdictions, electricity prices may be close to zero or occasionally negative on occasions that there is more electrical generation available than there is load available to absorb it; although at present this is rarely due to wind or solar power alone, increased wind and solar generation will increase the likelihood of such occurrences. It is particularly likely that pumped storage will become especially important as a balance for very large scale photovoltaic generation. Increased long distance transmission capacity combined with significant amounts of energy storage will be a crucial part of regulating any large-scale deployment of intermittent renewable power sources. The high non-firm renewable electricity penetration in some regions supplies 40% of annual output, but 60% may be reached before additional storage is necessary.


title: Pumped-storage hydroelectricity

text: Smaller pumped storage plants cannot achieve the same economies of scale as larger ones, but some do exist, including a recent 13 MW project in Germany. Shell Energy has proposed a 5 MW project in Washington State. Some have proposed small pumped storage plants in buildings, although these are not yet economical. Also, it is difficult to fit large reservoirs into the urban landscape. Nevertheless, some authors defend the technological simplicity and security of water supply as important externalities.


title: Pumped-storage hydroelectricity

text: The first use of pumped storage was in 1907 in Switzerland, at the Engeweiher pumped storage facility near Schaffhausen, Switzerland. In the 1930s reversible hydroelectric turbines became available. These turbines could operate as both turbine-generators and in reverse as electric motor driven pumps. The latest in large-scale engineering technology are variable speed machines for greater efficiency. These machines operate in synchronization with the network frequency when generating, but operate asynchronously (independent of the network frequency) when pumping.


title: Pumped-storage hydroelectricity

text: The first use of pumped-storage in the United States was in 1930 by the Connecticut Electric and Power Company, using a large reservoir located near New Milford, Connecticut, pumping water from the Housatonic River to the storage reservoir above.


title: Pumped-storage hydroelectricity

text: In 2009, world pumped storage generating capacity was 104 GW, while other sources claim 127 GW, which comprises the vast majority of all types of utility grade electric storage. The EU had 38.3 GW net capacity (36.8% of world capacity) out of a total of 140 GW of hydropower and representing 5% of total net electrical capacity in the EU. Japan had 25.5 GW net capacity (24.5% of world capacity).


title: Pumped-storage hydroelectricity

text: In 2010 the United States had 21.5 GW of pumped storage generating capacity (20.6% of world capacity). PSH contributed 21,073 GWh of energy in 2020 in the United States, but −5,321 GWh (net) because more energy is consumed in pumping than is generated. Nameplate pumped storage capacity had grown to 21.6 GW by 2014, with pumped storage comprising 97% of grid-scale energy storage in the United States. As of late 2014, there were 51 active project proposals with a total of 39 GW of new nameplate capacity across all stages of the FERC licensing process for new pumped storage hydroelectric plants in the United States, but no new plants were currently under construction in the United States at the time.


title: Pumped-storage hydroelectricity

text: The five largest operational pumped-storage plants are listed below "(for a detailed list see List of pumped-storage hydroelectric power stations)":


title: Pumped-storage hydroelectricity

text: In June 2018 the Australian federal government announced that 14 sites had been identified in Tasmania for pumped storage hydro, with the potential of adding 4.8GW to the national grid if a second interconnector beneath Bass Strait was constructed.


title: Pumped-storage hydroelectricity

text: Approvals have been granted for the Snowy 2.0 project, which will link two existing dams in the New South Wales Snowy Mountains to provide 2,000 MW of capacity and 350,000 MWh of storage.


title: Pumped-storage hydroelectricity

text: In September 2022, a pumped hydro electric storage (PHES) scheme was announced at Pioneer-Burdekin in central Queensland which has the potential to be the largest PHES in the world at 5GW.


title: Pumped-storage hydroelectricity

text: There are 9 power stations capable of pumping with a total installed capacity of 1344 MW and an average annual production of 2247 GWh. The pumped storage hydro power in Norway is built a bit different than the rest of the world. They are designed for seasonal pumping. Most of them can also not cycle the water endlessly, but only pump and reuse once. The reason for this is the design of the tunnels and elevation of lower and upper reservoir. Some, like Nygard power station, pump water from several river intakes up to a reservoir.


title: Pumped-storage hydroelectricity

text: The largest one, Saurdal, which is part of the Ulla-Førre complex, have four 160 MW Francis turbines, but only two are reversible. The lower reservoir is at higher elevation than the station itself, and thus the water pumped up can only be used once before it has to flow to the next station, Kvilldal, further down the tunnel system. And in addition to the lower reservoir it will receive water that can be pumped up from 23 river/stream and small reservoir intakes. Some which have already gone through a smaller power station on its way.


title: Pumped-storage hydroelectricity

text: Conventional hydroelectric dams may also make use of pumped storage in a hybrid system that both generates power from water naturally flowing into the reservoir as well as storing water pumped back to the reservoir from below the dam. The Grand Coulee Dam in the United States was expanded with a pump-back system in 1973. Existing dams may be repowered with reversing turbines thereby extending the length of time the plant can operate at capacity. Optionally a pump back powerhouse such as the Russell Dam (1992) may be added to a dam for increased generating capacity. Making use of an existing dam's upper reservoir and transmission system can expedite projects and reduce costs.


title: Pumped-storage hydroelectricity

text: In January 2019, the State Grid Corporation of China announced plans to invest US$5.7 billion in five pumped hydro storage plants with a total 6 GW capacity, to be located in Hebei, Jilin, Zhejiang, Shandong provinces, and in Xinjiang Autonomous Region. China is seeking to build 40 GW of pumped hydro capacity installed by 2020.


title: Pumped-storage hydroelectricity

text: Pumped storage plants can operate with seawater, although there are additional challenges compared to using fresh water, such as saltwater corrosion and barnacle growth. Inaugurated in 1966, the 240 MW Rance tidal power station in France can partially work as a pumped-storage station. When high tides occur at off-peak hours, the turbines can be used to pump more seawater into the reservoir than the high tide would have naturally brought in. It is the only large-scale power plant of its kind.


title: Pumped-storage hydroelectricity

text: In 1999, the 30 MW Yanbaru project in Okinawa was the first demonstration of seawater pumped storage. It has since been decommissioned. A 300 MW seawater-based Lanai Pumped Storage Project was considered for Lanai, Hawaii, and seawater-based projects have been proposed in Ireland. A pair of proposed projects in the Atacama Desert in northern Chile would use 600 MW of photovoltaic solar (Skies of Tarapacá) together with 300 MW of pumped storage (Mirror of Tarapacá) raising seawater up a coastal cliff.


title: Pumped-storage hydroelectricity

text: The use of underground reservoirs has been investigated. Recent examples include the proposed Summit project in Norton, Ohio, the proposed Maysville project in Kentucky (underground limestone mine), and the Mount Hope project in New Jersey, which was to have used a former iron mine as the lower reservoir. The proposed energy storage at the Callio site in Pyhäjärvi (Finland) would utilize the deepest base metal mine in Europe, with elevation difference. Several new underground pumped storage projects have been proposed. Cost-per-kilowatt estimates for these projects can be lower than for surface projects if they use existing underground mine space. There are limited opportunities involving suitable underground space, but the number of underground pumped storage opportunities may increase if abandoned coal mines prove suitable.


title: Pumped-storage hydroelectricity

text: In Bendigo, Victoria, Australia, the Bendigo Sustainability Group has proposed the use of the old gold mines under Bendigo for Pumped Hydro Energy Storage. Bendigo has the greatest concentration of deep shaft hard rock mines anywhere in the world with over 5,000 shafts sunk under Bendigo in the second half of the 19th Century. The deepest shaft extends 1,406 metres vertically underground. A recent pre-feasibility study has shown the concept to be viable with a generation capacity of 30 MW and a run time of 6 hours using a water head of over 750 metres.


title: Pumped-storage hydroelectricity

text: US-based start-up Quidnet Energy is exploring using abandoned oil and gas wells for pumped-storage. If successful, they hope to scale up to using many or most of the 3 million abandoned wells in the US.


title: Pumped-storage hydroelectricity

text: Small (or micro) applications for pumped-storage could be built on streams and within infrastructures, such as drinking water networks and artificial snow making infrastructures. In this regard, a storm-water basin has been concretely implemented as a cost-effective solution for a water reservoir in a micro pumped hydro energy storage. Such plants provide distributed energy storage and distributed flexible electricity production and can contribute to the decentralized integration of intermittent renewable energy technologies, such as wind power and solar power. Reservoirs that can be used for small pumped-storage hydropower plants could include natural or artificial lakes, reservoirs within other structures such as irrigation, or unused portions of mines or underground military installations. In Switzerland one study suggested that the total installed capacity of small pumped-storage hydropower plants in 2011 could be increased by 3 to 9 times by providing adequate policy instruments.


title: Pumped-storage hydroelectricity

text: In March 2017 the research project StEnSea (Storing Energy at Sea) announced their successful completion of a four-week test of a pumped storage underwater reservoir. In this configuration a hollow sphere submerged and anchored at great depth acts as the lower reservoir, while the upper reservoir is the enclosing body of water. Electricity is created when water is let in via a reversible turbine integrated into the sphere. During off-peak hours the turbine changes direction and pumps the water out again, using "surplus" electricity from the grid. The quantity of power created when water is let in grows proportionally to the height of the column of water above the sphere, in other words: the deeper the sphere is located, the more densely it can store energy.


title: Pumped-storage hydroelectricity

text: As such the energy storage capacity of the submerged reservoir is not governed by the gravitational energy in the traditional sense, but rather by the vertical pressure variation.


title: Pumped-storage hydroelectricity

text: While StEnSea's test took place at a depth of 100 m in the fresh water Lake Constance, the technology is foreseen to be used in salt water at greater depths. Since the submerged reservoir needs only a connecting electrical cable, the depth at which it can be employed is limited only by the depth at which the turbine can function, currently limited to 700 m. The challenge of designing salt water pumped storage in this underwater configuration brings a range of advantages:


title: Pumped-storage hydroelectricity

text: A current commercial design featuring a sphere with an inner diameter of 30 m submerged to 700 m would correspond to a 20 MWh capacity which with a 5 MW turbine would lead to a 4-hour discharge time. An energy park with multiple such reservoirs would bring the storage cost to around a few eurocents per kWh with construction and equipment costs in the range €1,200-€1,400 per kW. To avoid excessive transmission cost and loss, the reservoirs should be placed off deep water coasts of densely populated areas, such as Norway, Spain, United States and Japan. With this limitation the concept would allow for worldwide electricity storage of close to 900 GWh.


title: Pumped-storage hydroelectricity

text: For comparison, a traditional, gravity-based pumped storage capable of storing 20 MWh in a water reservoir the size of a 30 m sphere would need a hydraulic head of 519 m with the elevation spanned by a pressurized water pipe requiring typically a hill or mountain for support.


title: Pumped-storage hydroelectricity

text: Using a pumped-storage system of cisterns and small generators, pico hydro may also be effective for "closed loop" home energy generation systems.


title: Pumped-storage hydroelectricity

text: Using hydraulic fracturing pressure can be stored underground in strata such as shale. The shale used contains no hydrocarbons.


title: Acid dissociation constant

text: In chemistry, an acid dissociation constant (also known as acidity constant, or acid-ionization constant; denoted ) is a quantitative measure of the strength of an acid in solution. It is the equilibrium constant for a chemical reaction


title: Acid dissociation constant

text: known as dissociation in the context of acid–base reactions. The chemical species HA is an acid that dissociates into , the conjugate base of the acid and a hydrogen ion, . The system is said to be in equilibrium when the concentrations of its components will not change over time, because both forward and backward reactions are occurring at the same rate.


title: Acid dissociation constant

text: The acid dissociation constant for an acid is a direct consequence of the underlying thermodynamics of the dissociation reaction; the p"K" value is directly proportional to the standard Gibbs free energy change for the reaction. The value of the p"K" changes with temperature and can be understood qualitatively based on Le Châtelier's principle: when the reaction is endothermic, "K" increases and p"K" decreases with increasing temperature; the opposite is true for exothermic reactions.


title: Acid dissociation constant

text: The value of p"K" also depends on molecular structure of the acid in many ways. For example, Pauling proposed two rules: one for successive p"K" of polyprotic acids (see Polyprotic acids below), and one to estimate the p"K" of oxyacids based on the number of =O and −OH groups (see Factors that affect p"K" values below). Other structural factors that influence the magnitude of the acid dissociation constant include inductive effects, mesomeric effects, and hydrogen bonding. Hammett type equations have frequently been applied to the estimation of p"K".


title: Acid dissociation constant

text: The quantitative behaviour of acids and bases in solution can be understood only if their p"K" values are known. In particular, the pH of a solution can be predicted when the analytical concentration and p"K" values of all acids and bases are known; conversely, it is possible to calculate the equilibrium concentration of the acids and bases in solution when the pH is known. These calculations find application in many different areas of chemistry, biology, medicine, and geology. For example, many compounds used for medication are weak acids or bases, and a knowledge of the p"K" values, together with the octanol-water partition coefficient, can be used for estimating the extent to which the compound enters the blood stream. Acid dissociation constants are also essential in aquatic chemistry and chemical oceanography, where the acidity of water plays a fundamental role. In living organisms, acid–base homeostasis and enzyme kinetics are dependent on the p"K" values of the many acids and bases present in the cell and in the body. In chemistry, a knowledge of p"K" values is necessary for the preparation of buffer solutions and is also a prerequisite for a quantitative understanding of the interaction between acids or bases and metal ions to form complexes. Experimentally, p"K" values can be determined by potentiometric (pH) titration, but for values of p"K" less than about 2 or more than about 11, spectrophotometric or NMR measurements may be required due to practical difficulties with pH measurements.


title: Acid dissociation constant

text: According to Arrhenius's original molecular definition, an acid is a substance that dissociates in aqueous solution, releasing the hydrogen ion (a proton):


title: Acid dissociation constant

text: The equilibrium constant for this dissociation reaction is known as a dissociation constant. The liberated proton combines with a water molecule to give a hydronium (or oxonium) ion (naked protons do not exist in solution), and so Arrhenius later proposed that the dissociation should be written as an acid–base reaction:


title: Acid dissociation constant

text: The acid loses a proton, leaving a conjugate base; the proton is transferred to the base, creating a conjugate acid. For aqueous solutions of an acid HA, the base is water; the conjugate base is and the conjugate acid is the hydronium ion. The Brønsted–Lowry definition applies to other solvents, such as dimethyl sulfoxide: the solvent S acts as a base, accepting a proton and forming the conjugate acid .


title: Acid dissociation constant

text: In solution chemistry, it is common to use as an abbreviation for the solvated hydrogen ion, regardless of the solvent. In aqueous solution denotes a solvated hydronium ion rather than a proton.


title: Acid dissociation constant

text: The designation of an acid or base as "conjugate" depends on the context. The conjugate acid of a base B dissociates according to


title: Acid dissociation constant

text: The hydroxide ion , a well known base, is here acting as the conjugate base of the acid water. Acids and bases are thus regarded simply as donors and acceptors of protons respectively.


title: Acid dissociation constant

text: A broader definition of acid dissociation includes hydrolysis, in which protons are produced by the splitting of water molecules. For example, boric acid () produces as if it were a proton donor, but it has been confirmed by Raman spectroscopy that this is due to the hydrolysis equilibrium:


title: Acid dissociation constant

text: According to Lewis's original definition, an acid is a substance that accepts an electron pair to form a coordinate covalent bond.


title: Acid dissociation constant

text: An acid dissociation constant is a particular example of an equilibrium constant. The dissociation of a monoprotic acid, HA, in dilute solution can be written as


title: Acid dissociation constant

text: where represents the activity, at equilibrium, of the chemical species X. is dimensionless since activity is dimensionless. Activities of the products of dissociation are placed in the numerator, activities of the reactants are placed in the denominator. See activity coefficient for a derivation of this expression.


title: Acid dissociation constant

text: Since activity is the product of concentration and activity coefficient ("γ") the definition could also be written as


title: Acid dissociation constant

text: To avoid the complications involved in using activities, dissociation constants are determined, where possible, in a medium of high ionic strength, that is, under conditions in which can be assumed to be always constant. For example, the medium might be a solution of 0.1 molar (M) sodium nitrate or 3 M potassium perchlorate. With this assumption,


title: Acid dissociation constant

text: is obtained. Note, however, that all published dissociation constant values refer to the specific ionic medium used in their determination and that different values are obtained with different conditions, as shown for acetic acid in the illustration above. When published constants refer to an ionic strength other than the one required for a particular application, they may be adjusted by means of specific ion theory (SIT) and other theories.


title: Acid dissociation constant

text: A cumulative equilibrium constant, denoted by is related to the product of stepwise constants, denoted by For a dibasic acid the relationship between stepwise and overall constants is as follows


title: Acid dissociation constant

text: Note that in the context of metal-ligand complex formation, the equilibrium constants for the formation of metal complexes are usually defined as "association" constants. In that case, the equilibrium constants for ligand protonation are also defined as association constants. The numbering of association constants is the reverse of the numbering of dissociation constants; in this example formula_11


title: Acid dissociation constant

text: When discussing the properties of acids it is usual to specify equilibrium constants as acid dissociation constants, denoted by "K", with numerical values given the symbol p"K".


title: Acid dissociation constant

text: However, general purpose computer programs that are used to derive equilibrium constant values from experimental data use association constants for both acids and bases. Because stability constants for a metal-ligand complex are always specified as association constants, ligand protonation must also be specified as an association reaction. The definitions show that the value of an acid dissociation constant is the reciprocal of the value of the corresponding association constant.


title: Acid dissociation constant

text: The standard enthalpy change for a reaction is itself a function of temperature, according to Kirchhoff's law of thermochemistry:


title: Acid dissociation constant

text: where is the heat capacity change at constant pressure. In practice may be taken to be constant over a small temperature range.


title: Acid dissociation constant

text: "K" appears to have dimensions of concentration. However, since formula_21, the equilibrium constant, , "cannot" have a physical dimension. This apparent paradox can be resolved in various ways.


title: Acid dissociation constant

text: The procedures, (1) and (2), give identical numerical values for an equilibrium constant. Furthermore, since a concentration is simply proportional to mole fraction and density :


title: Acid dissociation constant

text: and since the molar mass is a constant in dilute solutions, an equilibrium constant value determined using (3) will be simply proportional to the values obtained with (1) and (2).


title: Acid dissociation constant

text: It is common practice in biochemistry to quote a value with a dimension as, for example, ""K" = 30 mM" in order to indicate the scale, millimolar (mM) or micromolar (μM) of the concentration values used for its calculation.


title: Acid dissociation constant

text: An acid is classified as "strong" when the concentration of its undissociated species is too low to be measured. Any aqueous acid with a p"K" value of less than 0 is almost completely deprotonated and is considered a "strong acid". All such acids transfer their protons to water and form the solvent cation species (HO in aqueous solution) so that they all have essentially the same acidity, a phenomenon known as solvent leveling. They are said to be "fully dissociated" in aqueous solution because the amount of undissociated acid, in equilibrium with the dissociation products, is below the detection limit.


title: Acid dissociation constant

text: Likewise, any aqueous base with an association constant p"K" less than about 0, corresponding to p"K" greater than about 14, is leveled to OH and is considered a "strong base".


title: Acid dissociation constant

text: Nitric acid, with a p"K" value of ca. -1.7, behaves as a strong acid in aqueous solutions with a pH greater than 1. At lower pH values it behaves as a weak acid.


title: Acid dissociation constant

text: p"K" values for strong acids have been estimated by theoretical means. For example, the p"K" value of aqueous HCl has been estimated as −9.3.


title: Acid dissociation constant

text: In water, measurable p"K" values range from about −2 for a strong acid to about 12 for a very weak acid (or strong base).


title: Acid dissociation constant

text: A buffer solution of a desired pH can be prepared as a mixture of a weak acid and its conjugate base. In practice, the mixture can be created by dissolving the acid in water, and adding the requisite amount of strong acid or base. When the p"K" and analytical concentration of the acid are known, the extent of dissociation and pH of a solution of a monoprotic acid can be easily calculated using an ICE table.


title: Acid dissociation constant

text: A polyprotic acid is a compound which may lose more than 1 proton. Stepwise dissociation constants are each defined for the loss of a single proton. The constant for dissociation of the first proton may be denoted as "K" and the constants for dissociation of successive protons as "K", etc. Phosphoric acid, , is an example of a polyprotic acid as it can lose three protons.


title: Acid dissociation constant

text: When the difference between successive p"K" values is about four or more, as in this example, each species may be considered as an acid in its own right; In fact salts of may be crystallised from solution by adjustment of pH to about 5.5 and salts of may be crystallised from solution by adjustment of pH to about 10. The species distribution diagram shows that the concentrations of the two ions are maximum at pH 5.5 and 10.


title: Acid dissociation constant

text: When the difference between successive p"K" values is less than about four there is overlap between the pH range of existence of the species in equilibrium. The smaller the difference, the more the overlap. The case of citric acid is shown at the right; solutions of citric acid are buffered over the whole range of pH 2.5 to 7.5.


title: Acid dissociation constant

text: According to Pauling's first rule, successive p"K" values of a given acid increase . For oxyacids with more than one ionizable hydrogen on the same atom, the p"K" values often increase by about 5 units for each proton removed, as in the example of phosphoric acid above.


title: Acid dissociation constant

text: It can be seen in the table above that the second proton is removed from a negatively charged species. Since the proton carries a positive charge extra work is needed to remove it. That why p"K" is greater than p"K". p"K" is greater than p"K" because there is further charge separation. When an exception to Pauling's rule is found, it indicates that a major change in structure is also occurring. In the case of (aq), the vanadium is octahedral, 6-coordinate, whereas vanadic acid is tetrahedral, 4-coordinate. This means that four "particles" are released with the first dissociation, but only two "particles" are released with the other dissociations, resulting in a much greater entropy contribution to the standard Gibbs free energy change for the first reaction than for the others.


title: Acid dissociation constant

text: For substances in solution, the isoelectric point (p"I") is defined as the pH at which the sum, weighted by charge value, of concentrations of positively charged species is equal to the weighted sum of concentrations of negatively charged species. In the case that there is one species of each type, the isoelectric point can be obtained directly from the p"K" values. Take the example of glycine, defined as AH. There are two dissociation equilibria to consider.


title: Acid dissociation constant

text: At the isoelectric point the concentration of the positively charged species, , is equal to the concentration of the negatively charged species, , so


title: Acid dissociation constant

text: p"I" values for amino acids are listed at proteinogenic amino acid. When more than two charged species are in equilibrium with each other a full speciation calculation may be needed.


title: Acid dissociation constant

text: The equilibrium constant "K" for a base is usually defined as the "association" constant for protonation of the base, B, to form the conjugate acid, .


title: Acid dissociation constant

text: "K" is related to "K" for the conjugate acid. In water, the concentration of the hydroxide ion, , is related to the concentration of the hydrogen ion by , therefore


title: Acid dissociation constant

text: When "K", "K" and "K" are determined under the same conditions of temperature and ionic strength, it follows, taking cologarithms, that p"K" = p"K" − p"K". In aqueous solutions at 25 °C, p"K" is 13.9965, so


title: Acid dissociation constant

text: with sufficient accuracy for most practical purposes. In effect there is no need to define p"K" separately from p"K", but it is done here as often only p"K" values can be found in the older literature.


title: Acid dissociation constant

text: Because the relationship p"K" = p"K" − p"K" holds only in aqueous solutions (though analogous relationships apply for other amphoteric solvents), subdisciplines of chemistry like organic chemistry that usually deal with nonaqueous solutions generally do not use p"K" as a measure of basicity. Instead, the p"K" of the conjugate acid, denoted by p"K", is quoted when basicity needs to be quantified. For base B and its conjugate acid BH in equilibrium, this is defined as


title: Acid dissociation constant

text: A higher value for p"K" corresponds to a stronger base. For example, the values and indicate that (triethylamine) is a stronger base than (pyridine).


title: Acid dissociation constant

text: An amphoteric substance is one that can act as an acid or as a base, depending on pH. Water (below) is amphoteric. Another example of an amphoteric molecule is the bicarbonate ion that is the conjugate base of the carbonic acid molecule H2CO3 in the equilibrium


title: Acid dissociation constant

text: An amino acid is also amphoteric with the added complication that the neutral molecule is subject to an internal acid–base equilibrium in which the basic amino group attracts and binds the proton from the acidic carboxyl group, forming a zwitterion.


title: Acid dissociation constant

text: At pH less than about 5 both the carboxylate group and the amino group are protonated. As pH increases the acid dissociates according to


title: Acid dissociation constant

text: The water molecule may either gain or lose a proton. It is said to be amphiprotic. The ionization equilibrium can be written


title: Acid dissociation constant

text: where in aqueous solution denotes a solvated proton. Often this is written as the hydronium ion , but this formula is not exact because in fact there is solvation by more than one water molecule and species such as , , and are also present.


title: Acid dissociation constant

text: With solutions in which the solute concentrations are not very high, the concentration can be assumed to be constant, regardless of solute(s); this expression may then be replaced by


title: Acid dissociation constant

text: The self-ionization constant of water, "K", is thus just a special case of an acid dissociation constant. A logarithmic form analogous to p"K" may also be defined


title: Acid dissociation constant

text: From this equation, p"K" = 14 at 24.87 °C. At that temperature both hydrogen and hydroxide ions have a concentration of 10 M.


title: Acid dissociation constant

text: A solvent will be more likely to promote ionization of a dissolved acidic molecule in the following circumstances:


title: Acid dissociation constant

text: p"K" values of organic compounds are often obtained using the aprotic solvents dimethyl sulfoxide (DMSO) and acetonitrile (ACN).


title: Acid dissociation constant

text: DMSO is widely used as an alternative to water because it has a lower dielectric constant than water, and is less polar and so dissolves non-polar, hydrophobic substances more easily. It has a measurable p"K" range of about 1 to 30. Acetonitrile is less basic than DMSO, and, so, in general, acids are weaker and bases are stronger in this solvent. Some p"K" values at 25 °C for acetonitrile (ACN) and dimethyl sulfoxide (DMSO). are shown in the following tables. Values for water are included for comparison.


title: Acid dissociation constant

text: Ionization of acids is less in an acidic solvent than in water. For example, hydrogen chloride is a weak acid when dissolved in acetic acid. This is because acetic acid is a much weaker base than water.


title: Acid dissociation constant

text: Compare this reaction with what happens when acetic acid is dissolved in the more acidic solvent pure sulfuric acid:


title: Acid dissociation constant

text: The unlikely geminal diol species is stable in these environments. For aqueous solutions the pH scale is the most convenient acidity function. Other acidity functions have been proposed for non-aqueous media, the most notable being the Hammett acidity function, "H", for superacid media and its modified version "H" for superbasic media.


title: Acid dissociation constant

text: In aprotic solvents, oligomers, such as the well-known acetic acid dimer, may be formed by hydrogen bonding. An acid may also form hydrogen bonds to its conjugate base. This process, known as homoconjugation, has the effect of enhancing the acidity of acids, lowering their effective p"K" values, by stabilizing the conjugate base. Homoconjugation enhances the proton-donating power of toluenesulfonic acid in acetonitrile solution by a factor of nearly 800.


title: Acid dissociation constant

text: In aqueous solutions, homoconjugation does not occur, because water forms stronger hydrogen bonds to the conjugate base than does the acid.


title: Acid dissociation constant

text: When a compound has limited solubility in water it is common practice (in the pharmaceutical industry, for example) to determine p"K" values in a solvent mixture such as water/dioxane or water/methanol, in which the compound is more soluble. In the example shown at the right, the p"K" value rises steeply with increasing percentage of dioxane as the dielectric constant of the mixture is decreasing.


title: Acid dissociation constant

text: A p"K" value obtained in a mixed solvent cannot be used directly for aqueous solutions. The reason for this is that when the solvent is in its standard state its activity is "defined" as one. For example, the standard state of water:dioxane mixture with 9:1 mixing ratio is precisely that solvent mixture, with no added solutes. To obtain the p"K" value for use with aqueous solutions it has to be extrapolated to zero co-solvent concentration from values obtained from various co-solvent mixtures.


title: Acid dissociation constant

text: These facts are obscured by the omission of the solvent from the expression that is normally used to define p"K", but p"K" values obtained in a "given" mixed solvent can be compared to each other, giving relative acid strengths. The same is true of p"K" values obtained in a particular non-aqueous solvent such a DMSO.


title: Acid dissociation constant

text: A universal, solvent-independent, scale for acid dissociation constants has not been developed, since there is no known way to compare the standard states of two different solvents.


title: Acid dissociation constant

text: Pauling's second rule is that the value of the first p"K" for acids of the formula XO(OH) depends primarily on the number of oxo groups "m", and is approximately independent of the number of hydroxy groups "n", and also of the central atom X. Approximate values of p"K" are 8 for "m" = 0, 2 for "m" = 1, −3 for "m" = 2 and < −10 for "m" = 3. Alternatively, various numerical formulas have been proposed including p"K" = 8 − 5"m" (known as Bell's rule), p"K" = 7 − 5"m", or p"K" = 9 − 7"m". The dependence on "m" correlates with the oxidation state of the central atom, X: the higher the oxidation state the stronger the oxyacid. For example, p"K" for HClO is 7.2, for HClO is 2.0, for HClO is −1 and HClO is a strong acid (). The increased acidity on adding an oxo group is due to stabilization of the conjugate base by delocalization of its negative charge over an additional oxygen atom. This rule can help assign molecular structure: for example, phosphorous acid (HPO) has a p"K" near 2, which suggested that the structure is HPO(OH), as later confirmed by NMR spectroscopy, and not P(OH), which would be expected to have a p"K" near 8.


title: Acid dissociation constant

text: With organic acids inductive effects and mesomeric effects affect the p"K" values. A simple example is provided by the effect of replacing the hydrogen atoms in acetic acid by the more electronegative chlorine atom. The electron-withdrawing effect of the substituent makes ionisation easier, so successive p"K" values decrease in the series 4.7, 2.8, 1.4, and 0.7 when 0, 1, 2, or 3 chlorine atoms are present. The Hammett equation, provides a general expression for the effect of substituents.


title: Acid dissociation constant

text: "K" is the dissociation constant of a substituted compound, "K" is the dissociation constant when the substituent is hydrogen, ρ is a property of the unsubstituted compound and σ has a particular value for each substituent. A plot of log("K") against σ is a straight line with intercept log("K") and slope ρ. This is an example of a linear free energy relationship as log("K") is proportional to the standard free energy change. Hammett originally formulated the relationship with data from benzoic acid with different substituents in the "ortho-" and "para-" positions: some numerical values are in Hammett equation. This and other studies allowed substituents to be ordered according to their electron-withdrawing or electron-releasing power, and to distinguish between inductive and mesomeric effects.


title: Acid dissociation constant

text: Alcohols do not normally behave as acids in water, but the presence of a double bond adjacent to the OH group can substantially decrease the p"K" by the mechanism of keto–enol tautomerism. Ascorbic acid is an example of this effect. The diketone 2,4-pentanedione (acetylacetone) is also a weak acid because of the keto–enol equilibrium. In aromatic compounds, such as phenol, which have an OH substituent, conjugation with the aromatic ring as a whole greatly increases the stability of the deprotonated form.


title: Acid dissociation constant

text: Structural effects can also be important. The difference between fumaric acid and maleic acid is a classic example. Fumaric acid is (E)-1,4-but-2-enedioic acid, a "trans" isomer, whereas maleic acid is the corresponding "cis" isomer, i.e. (Z)-1,4-but-2-enedioic acid (see cis-trans isomerism). Fumaric acid has p"K" values of approximately 3.0 and 4.5. By contrast, maleic acid has p"K" values of approximately 1.5 and 6.5. The reason for this large difference is that when one proton is removed from the "cis" isomer (maleic acid) a strong intramolecular hydrogen bond is formed with the nearby remaining carboxyl group. This favors the formation of the maleate H, and it opposes the removal of the second proton from that species. In the "trans" isomer, the two carboxyl groups are always far apart, so hydrogen bonding is not observed.


title: Acid dissociation constant

text: Proton sponge, 1,8-bis(dimethylamino)naphthalene, has a p"K" value of 12.1. It is one of the strongest amine bases known. The high basicity is attributed to the relief of strain upon protonation and strong internal hydrogen bonding.


title: Acid dissociation constant

text: Effects of the solvent and solvation should be mentioned also in this section. It turns out, these influences are more subtle than that of a dielectric medium mentioned above. For example, the expected (by electronic effects of methyl substituents) and observed in gas phase order of basicity of methylamines, MeN > MeNH > MeNH > NH, is changed by water to MeNH > MeNH > MeN > NH. Neutral methylamine molecules are hydrogen-bonded to water molecules mainly through one acceptor, N–HOH, interaction and only occasionally just one more donor bond, NH–OH. Hence, methylamines are stabilized to about the same extent by hydration, regardless of the number of methyl groups. In stark contrast, corresponding methylammonium cations always utilize all the available protons for donor NH–OH bonding. Relative stabilization of methylammonium ions thus decreases with the number of methyl groups explaining the order of water basicity of methylamines.


title: Acid dissociation constant

text: An equilibrium constant is related to the standard Gibbs energy change for the reaction, so for an acid dissociation constant


title: Acid dissociation constant

text: "R" is the gas constant and "T" is the absolute temperature. Note that and . At 25 °C, Δ"G" in kJ·mol ≈ 5.708 p"K" (1 kJ·mol = 1000 joules per mole). Free energy is made up of an enthalpy term and an entropy term.


title: Acid dissociation constant

text: The standard enthalpy change can be determined by calorimetry or by using the van 't Hoff equation, though the calorimetric method is preferable. When both the standard enthalpy change and acid dissociation constant have been determined, the standard entropy change is easily calculated from the equation above. In the following table, the entropy terms are calculated from the experimental values of p"K" and Δ"H". The data were critically selected and refer to 25 °C and zero ionic strength, in water.


title: Acid dissociation constant

text: The first point to note is that, when p"K" is positive, the standard free energy change for the dissociation reaction is also positive. Second, some reactions are exothermic and some are endothermic, but, when Δ"H" is negative "T"ΔS is the dominant factor, which determines that Δ"G" is positive. Last, the entropy contribution is always unfavourable () in these reactions. Ions in aqueous solution tend to orient the surrounding water molecules, which orders the solution and decreases the entropy. The contribution of an ion to the entropy is the partial molar entropy which is often negative, especially for small or highly charged ions. The ionization of a neutral acid involves formation of two ions so that the entropy decreases (). On the second ionization of the same acid, there are now three ions and the anion has a charge, so the entropy again decreases.


title: Acid dissociation constant

text: Note that the "standard" free energy change for the reaction is for the changes "from" the reactants in their standard states "to" the products in their standard states. The free energy change "at" equilibrium is zero since the chemical potentials of reactants and products are equal at equilibrium.


title: Acid dissociation constant

text: The experimental determination of p"K" values is commonly performed by means of titrations, in a medium of high ionic strength and at constant temperature. A typical procedure would be as follows. A solution of the compound in the medium is acidified with a strong acid to the point where the compound is fully protonated. The solution is then titrated with a strong base until all the protons have been removed. At each point in the titration pH is measured using a glass electrode and a pH meter. The equilibrium constants are found by fitting calculated pH values to the observed values, using the method of least squares.


title: Acid dissociation constant

text: The total volume of added strong base should be small compared to the initial volume of titrand solution in order to keep the ionic strength nearly constant. This will ensure that p"K" remains invariant during the titration.


title: Acid dissociation constant

text: A calculated titration curve for oxalic acid is shown at the right. Oxalic acid has p"K" values of 1.27 and 4.27. Therefore, the buffer regions will be centered at about pH 1.3 and pH 4.3. The buffer regions carry the information necessary to get the p"K" values as the concentrations of acid and conjugate base change along a buffer region.


title: Acid dissociation constant

text: Between the two buffer regions there is an end-point, or equivalence point, at about pH 3. This end-point is not sharp and is typical of a diprotic acid whose buffer regions overlap by a small amount: p"K" − p"K" is about three in this example. (If the difference in p"K" values were about two or less, the end-point would not be noticeable.) The second end-point begins at about pH 6.3 and is sharp. This indicates that all the protons have been removed. When this is so, the solution is not buffered and the pH rises steeply on addition of a small amount of strong base. However, the pH does not continue to rise indefinitely. A new buffer region begins at about pH 11 (p"K" − 3), which is where self-ionization of water becomes important.


title: Acid dissociation constant

text: It is very difficult to measure pH values of less than two in aqueous solution with a glass electrode, because the Nernst equation breaks down at such low pH values. To determine p"K" values of less than about 2 or more than about 11 spectrophotometric or NMR measurements may be used instead of, or combined with, pH measurements.


title: Acid dissociation constant

text: When the glass electrode cannot be employed, as with non-aqueous solutions, spectrophotometric methods are frequently used. These may involve absorbance or fluorescence measurements. In both cases the measured quantity is assumed to be proportional to the sum of contributions from each photo-active species; with absorbance measurements the Beer–Lambert law is assumed to apply.


title: Acid dissociation constant

text: Isothermal titration calorimetry (ITC) may be used to determine both a p"K" value and the corresponding standard enthalpy for acid dissociation. Software to perform the calculations is supplied by the instrument manufacturers for simple systems.


title: Acid dissociation constant

text: Aqueous solutions with normal water cannot be used for H NMR measurements but heavy water, , must be used instead. C NMR data, however, can be used with normal water and H NMR spectra can be used with non-aqueous media. The quantities measured with NMR are time-averaged chemical shifts, as proton exchange is fast on the NMR time-scale. Other chemical shifts, such as those of P can be measured.


title: Acid dissociation constant

text: For some molecules, dissociation (or association) can occur at more than one nonequivalent site, and the observed macroscopic equilibrium constant or macroconstant is a combination of microconstants involving distinct species. When one reactant forms two products in parallel, the macroconstant is a sum of two microconstants, formula_41 This is true for example for the deprotonation of the amino acid cysteine, which exists in solution as a neutral zwitterion . The two microconstants represent deprotonation either at sulphur or at nitrogen, and the macroconstant sum here is the acid dissociation constant formula_42


title: Acid dissociation constant

text: Similarly, a base such as spermine has more than one site where protonation can occur. For example, monoprotonation can occur at a terminal group or at internal groups. The "K" values for dissociation of spermine protonated at one or other of the sites are examples of micro-constants. They cannot be determined directly by means of pH, absorbance, fluorescence or NMR measurements; a measured "K" value is the sum of the K values for the micro-reactions.


title: Acid dissociation constant

text: Nevertheless, the site of protonation is very important for biological function, so mathematical methods have been developed for the determination of micro-constants.


title: Acid dissociation constant

text: When two reactants form a single product in parallel, the macroconstant formula_44 For example, the abovementioned equilibrium for spermine may be considered in terms of "K" values of two tautomeric conjugate acids, with macroconstant In this case formula_45 This is equivalent to the preceding expression since formula_46 is proportional to formula_47


title: Acid dissociation constant

text: When a reactant undergoes two reactions in series, the macroconstant for the combined reaction is the product of the microconstant for the two steps. For example, the abovementioned cysteine zwitterion can lose two protons, one from sulphur and one from nitrogen, and the overall macroconstant for losing two protons is the product of two dissociation constants formula_48 This can also be written in terms of logarithmic constants as formula_49


title: Acid dissociation constant

text: A knowledge of p"K" values is important for the quantitative treatment of systems involving acid–base equilibria in solution. Many applications exist in biochemistry; for example, the p"K" values of proteins and amino acid side chains are of major importance for the activity of enzymes and the stability of proteins. Protein p"K" values cannot always be measured directly, but may be calculated using theoretical methods. Buffer solutions are used extensively to provide solutions at or near the physiological pH for the study of biochemical reactions; the design of these solutions depends on a knowledge of the p"K" values of their components. Important buffer solutions include MOPS, which provides a solution with pH 7.2, and tricine, which is used in gel electrophoresis. Buffering is an essential part of acid base physiology including acid–base homeostasis, and is key to understanding disorders such as acid–base disorder. The isoelectric point of a given molecule is a function of its p"K" values, so different molecules have different isoelectric points. This permits a technique called isoelectric focusing, which is used for separation of proteins by 2-D gel polyacrylamide gel electrophoresis.


title: Acid dissociation constant

text: Buffer solutions also play a key role in analytical chemistry. They are used whenever there is a need to fix the pH of a solution at a particular value. Compared with an aqueous solution, the pH of a buffer solution is relatively insensitive to the addition of a small amount of strong acid or strong base. The buffer capacity of a simple buffer solution is largest when pH = p"K". In acid–base extraction, the efficiency of extraction of a compound into an organic phase, such as an ether, can be optimised by adjusting the pH of the aqueous phase using an appropriate buffer. At the optimum pH, the concentration of the electrically neutral species is maximised; such a species is more soluble in organic solvents having a low dielectric constant than it is in water. This technique is used for the purification of weak acids and bases.


title: Acid dissociation constant

text: A pH indicator is a weak acid or weak base that changes colour in the transition pH range, which is approximately p"K" ± 1. The design of a universal indicator requires a mixture of indicators whose adjacent p"K" values differ by about two, so that their transition pH ranges just overlap.


title: Acid dissociation constant

text: In pharmacology, ionization of a compound alters its physical behaviour and macro properties such as solubility and lipophilicity, log "p"). For example, ionization of any compound will increase the solubility in water, but decrease the lipophilicity. This is exploited in drug development to increase the concentration of a compound in the blood by adjusting the p"K" of an ionizable group.


title: Acid dissociation constant

text: Knowledge of p"K" values is important for the understanding of coordination complexes, which are formed by the interaction of a metal ion, M, acting as a Lewis acid, with a ligand, L, acting as a Lewis base. However, the ligand may also undergo protonation reactions, so the formation of a complex in aqueous solution could be represented symbolically by the reaction


title: Acid dissociation constant

text: To determine the equilibrium constant for this reaction, in which the ligand loses a proton, the p"K" of the protonated ligand must be known. In practice, the ligand may be polyprotic; for example EDTA can accept four protons; in that case, all p"K" values must be known. In addition, the metal ion is subject to hydrolysis, that is, it behaves as a weak acid, so the p"K" values for the hydrolysis reactions must also be known.


title: Acid dissociation constant

text: Assessing the hazard associated with an acid or base may require a knowledge of p"K" values. For example, hydrogen cyanide is a very toxic gas, because the cyanide ion inhibits the iron-containing enzyme cytochrome c oxidase. Hydrogen cyanide is a weak acid in aqueous solution with a p"K" of about 9. In strongly alkaline solutions, above pH 11, say, it follows that sodium cyanide is "fully dissociated" so the hazard due to the hydrogen cyanide gas is much reduced. An acidic solution, on the other hand, is very hazardous because all the cyanide is in its acid form. Ingestion of cyanide by mouth is potentially fatal, independently of pH, because of the reaction with cytochrome c oxidase.


title: Acid dissociation constant

text: In environmental science acid–base equilibria are important for lakes and rivers; for example, humic acids are important components of natural waters. Another example occurs in chemical oceanography: in order to quantify the solubility of iron(III) in seawater at various salinities, the p"K" values for the formation of the iron(III) hydrolysis products , and were determined, along with the solubility product of iron hydroxide.


title: Acid dissociation constant

text: There are multiple techniques to determine the p"K" of a chemical, leading to some discrepancies between different sources. Well measured values are typically within 0.1 units of each other. Data presented here were taken at 25 °C in water. More values can be found in the Thermodynamics section, above. A table of p"K" of carbon acids, measured in DMSO, can be found on the page on carbanions.


title: White Walker

text: A White Walker is a humanoid creature from the HBO television series "Game of Thrones", and the George R. R. Martin novel series "A Song of Ice and Fire" on which it is based. Primarily referred to as the Others in the novels, White Walkers are a supernatural threat to mankind who dwell north of The Wall in Westeros. "The Verge" named them among "the most visually iconic creatures on the show". White Walkers are also featured in the show's merchandising.


title: White Walker

text: Martin introduces the Others in the prologue of "A Game of Thrones" (1996), describing them as "Tall ... and gaunt and hard as old bones, with flesh pale as milk" with eyes "deeper and bluer than any human eyes, a blue that burned like ice". Accompanied by intense cold, they wear armor that "seemed to change color as it moved", and wield thin crystal swords capable of shattering steel. The Others move silently, and they speak their own language; Martin writes that their voices are "like the cracking of ice on a winter lake". In "A Storm of Swords" (2000), they are shown to be vulnerable to weapons made of dragonglass (obsidian), as Samwell Tarly kills one this way:


title: White Walker

text: In "A Dance with Dragons" (2011), Sam uncovers ancient record fragments which suggest that the Others are also vulnerable to something called "dragonsteel", which he and Jon Snow surmise is another term for Valyrian steel.


title: White Walker

text: Creatures killed by the Others soon reanimate as wights: undead with pallid skin, black hands, and glowing blue eyes similar to the Others'. Dragonglass has no effect on wights in the books (though it kills them in the TV series). Wights may be physically injured, but even dismembered parts remain animated, however they may be destroyed by fire. The humans who live in the north beyond the Wall—called "wildlings" by the inhabitants of Westeros—burn their dead so they will not become wights. Wildlings call the Others "White Walkers", unlike others in Westeros.


title: White Walker

text: In 2012, Chris Lackner wrote in "Dose", "Fans of the novels are eagerly awaiting Martin's final two installments of the seven-part series. In particular, they are eager to learn more about the White Walkers—or The Others—a mysterious, undead race seemingly bent on humanity's destruction."


title: White Walker

text: In the novels and the 2014 companion book "The World of Ice & Fire", Martin establishes that, millennia before the events of "A Song of Ice and Fire" series, a pact existed between the Children of the Forest (elf-like creatures) and the First Men (mankind). This was weakened by the emergence of the Others, an enigmatic and malevolent nonhuman species who inflicted a night that lasted a generation and a winter that lasted decades. After the Others were pushed back, the Children and the First Men raised The Wall, a vast barrier of stone, ice and magic from one coast of northern Westeros to the other, to bar the passage of the Others south.


title: White Walker

text: As "A Game of Thrones" (1996) begins, the general belief across Westeros is that the Others are a legend to scare children, or else "gone eight thousand years". But the Others have re-emerged, and are gaining power—and creating wights—beyond the Wall. In the Prologue, a ranging party from the Night's Watch come face to face with a group of the Others, who kill Ser Waymar Royce. Reanimated as a wight, he then kills the ranger Will. Out ranging beyond the Wall, Jon Snow and the Night's Watch find the corpses of two of their fallen brothers. Brought home to Castle Black, the dead men rise and kill several of their living fellows before they are destroyed.


title: White Walker

text: Sam Tarly kills an Other with a dragonglass dagger in "A Storm of Swords" (2000). His former comrade Small Paul is killed and reanimated as a wight. The undead Paul is unfazed by the dragonglass, but Sam is able to put him down with fire. Bran Stark recalls the story of the Night's King, a Stark and the 13th Lord Commander of the Night's Watch who had been seduced by a female White Walker. The Night's King and his queen enslaved the brothers of the Watch until the Starks and the wildlings joined forces to defeat him.


title: White Walker

text: Martin said in 2012 that readers will see more of the Others in his forthcoming novel "The Winds of Winter". He noted in a 2012 "Dose" interview, "[We'll learn more about their] history, certainly, but I don't know about culture ... I don't know if they have a culture".


title: White Walker

text: The White Walkers portrayed on HBO's "Game of Thrones" differ slightly in appearance from their literary counterparts, but Aaron Souppouris of "The Verge" named them among "the most visually iconic creatures on the show". In the TV series, the primary White Walker has been portrayed by Ross Mullan. The show calls them "White Walkers" to avoid confusing "the Others" and "others" in speech.


title: White Walker

text: Their apparent leader is the Night King, portrayed by Richard Brake and Vladimir Furdik, who first appeared in the episode "Oathkeeper", in which he places his hand on Craster's baby son, transforming him into a White Walker. In "Hardhome", the effectiveness of Valyrian steel against the White Walkers is proven as Jon shatters one to pieces with a single stroke of his ancient sword Longclaw. Unlike in the novels, the TV series has established that wights can be destroyed by dragonglass.


title: White Walker

text: In the season 6 episode "The Door" (May 2016), Bran Stark experiences a vision of the creation of the Night King by Leaf, one of the Children of the Forest, by stabbing a human prisoner in the chest with a dragonglass dagger. Leaf explains to an incredulous Bran that the Children were at war with the First Men at the time of the Night King's creation. In season 7, when Jon kills a White Walker, the wights under its control are also destroyed. The Night King kills Daenerys Targaryen's dragon Viserion in the seventh season episode "Beyond the Wall", and then reanimates him as a wight. In the season finale episode "The Dragon and the Wolf", the Night King uses the dragon to breach the Wall.


title: White Walker

text: In the eighth season premiere, "Winterfell", a group of survivors from the Wall's destruction discover that Last Hearth, the home of House Umber, has been attacked by the Army of the Dead in their conquest of the North, with all of its inhabitants killed. The Night King has also left a message in the form of the deceased Ned Umber impaled on a wall and surrounded by a spiral of severed limbs. In the second episode "A Knight of the Seven Kingdoms", the inhabitants of Winterfell make plans for defending the castle against the Army of the Dead. Bran states that the Night King is seeking an "endless night", as he plans to cleanse the world of all life and memory and intends to kill Bran as a major step towards this goal. The White Walkers are later seen viewing Winterfell from a distance as the living prepare to fight them.


title: White Walker

text: In the third episode "The Long Night", the Army of the Dead marches on Winterfell and nearly wipes out the combined armies of the living. The Night King eventually reaches the Godswood, kills Theon Greyjoy, and prepares to strike down Bran. However, the Night King is ambushed and killed by Arya Stark with the Valyrian steel dagger that Bran had previously given her ("The Spoils of War"), which causes both him and the other White Walkers to shatter and results in the complete obliteration of the Army of the Dead.


title: White Walker

text: In "House of the Dragon", the TV adaptation of "Fire & Blood", it is revealed in the first episode "The Heirs of the Dragon" that Aegon the Conqueror was inspired to unify Westeros by a dream in which he saw the end of the world of the living coming from the cold northernmost reaches of the continent.


title: White Walker

text: In 2012, Funko released a White Walker figure as part of their POP! Television line, which are 4.5 inch vinyl figures in the Japanese super deformed style. The company later produced a Mystery Mini Blind Box figurine of a stylized White Walker. Dark Horse released a 9-inch White Walker bust statue in 2013, and later a 9-inch full figure statue. In 2014, Funko released a 6.5 inch articulated White Walker action figure (with spear accessory) as part of their HBO-licensed Legacy Collection line, which features "some of the series’ most popular characters". In 2018, Johnnie Walker released White Walker, the first of several "Game of Thrones"-inspired whiskies.


title: 9K111 Fagot

text: The 9K111 "Fagot" (; "bassoon") is a second-generation tube-launched semi-automatic command to line of sight (SACLOS) wire-guided anti-tank missile system of the Soviet Union for use from ground or vehicle mounts. The 9K111 Fagot missile system was developed by the Tula KBP Design Bureau for Instrument Building. "9M111" is the GRAU designation of the missile. Its NATO reporting name is AT-4 Spigot.


title: 9K111 Fagot

text: The 9K111 Fagot was developed by the Tula Machinery Design Bureau (Tula KBP) and development began in 1962 with the aim of producing the next generation of SACLOS anti-tank guided missile (ATGM) for use in two roles: as man portable and tank destroyer. The 9K111 Fagot was developed alongside the 9M113 Konkurs; both missiles use similar technology, differing in size only, and can use the same launchers. The missile entered service in 1970.


title: 9K111 Fagot

text: The anti-tank platoon of a Soviet BTR equipped motor rifle battalion had two (sometimes three) ATGM squads, each with two 9K111 Fagot teams. The team consisted of three men; the gunner carries the 9P135 launcher and tripod as a back pack, and the other two men each carry two launch tubes. The men also carry assault rifles, but do not carry a rocket-propelled grenade (RPG), because unlike the earlier missiles there is only a small deadzone within which the missile cannot engage the target. Besides the four missiles carried by each team, each squad would normally have an extra eight missiles carried in their transport, usually a BTR. It can also be deployed from the BMP-1P, BMD-1P, BTR-D and UAZ-469.


title: 9K111 Fagot

text: North Korea was said to have acquired a number of the systems during the late 1980s until the 2000s. These were subsequently reverse-engineered under the designation Bulsae-2. It was advertised under designation AT-4MLB by North Korean proxy company GLOCOM, in brochure it was stated that it is controlled by laser beam guidance method, which was an upgrade designated Bulsae-3. Its use was first reported in 2014 in the ranks of the Izz ad-Din al-Qassam Brigades and the Al-Nasser Salah al-Deen Brigades.


title: 9K111 Fagot

text: The missile is stored and carried in a container/launch tube. It is fired from a 9P135 launcher post, a simple tripod. A 9S451 guidance box is fitted to the tripod with the missile sitting just above. The 9Sh119 sight is fitted to the left side (from the gunner's POV). The complete launcher system weighs . The gunner lays prone while firing. The system can engage moving targets travelling at less than . The launcher post can traverse through 360 degrees horizontally, and +/− 20 degrees in elevation. The sight has a magnification of 10x and a 5 degree field of view. Up to three missiles a minute can be fired from a launcher post.


title: 9K111 Fagot

text: The system uses a gas generator to push the missile out of the launch tube, which exits from the rear of the launch tube in a manner similar to a recoilless rifle. The missile leaves the launch tube at , and is then quickly accelerated to by its solid fuel motor. This initial high speed reduces the missile's deadzone, since it can be launched directly at the target, rather than in an upward arc.


title: 9K111 Fagot

text: The launcher tracks the position of an incandescent infrared bulb on the back of the missile relative to the target and transmits appropriate commands to the missile via a thin wire that trails behind the missile. The SACLOS guidance system has many benefits over manual command to line of sight (MCLOS), with the accuracy of the system stated as 90% in some sources, though its performance is probably comparable to the TOW or the later SACLOS versions of the 9K11 Malyutka.


title: Late Night with Conan O'Brien

text: Late Night with Conan O'Brien is an American late-night talk show hosted by Conan O'Brien. NBC aired 2,725 episodes from September 13, 1993, to February 20, 2009. The show featured varied comedic material, celebrity interviews, and musical and comedy performances. "Late Night" aired weeknights at 12:37 am Eastern/11:37 pm Central and 12:37 am Mountain in the United States. From 1993 until 2000, Andy Richter served as O'Brien's sidekick; following his departure, O'Brien was the show's sole featured performer. The show's house musical act was The Max Weinberg 7 and led by E Street Band drummer Max Weinberg.


title: Late Night with Conan O'Brien

text: The second incarnation of NBC's "Late Night" franchise, O'Brien's program debuted in 1993 after David Letterman (who hosted the first incarnation of "Late Night") moved to CBS to host "Late Show" opposite "The Tonight Show". In 2004, as part of a deal to secure a new contract, NBC announced that O'Brien would leave "Late Night" in 2009 to succeed Jay Leno as the host of "The Tonight Show". Jimmy Fallon began hosting his version of "Late Night" on March 2, 2009.


title: Late Night with Conan O'Brien

text: Upon Johnny Carson's retirement from "The Tonight Show" in 1992, executives at NBC announced that Carson's frequent guest-host Jay Leno would be Carson's replacement, and not David Letterman. NBC later said that Letterman's high ratings for "Late Night" were the reason they kept him where he was. Letterman was bitterly disappointed and angry at not having been given "The Tonight Show" job; and, at Carson's advice, he left NBC after eleven years on "Late Night". CBS signed Letterman to host his own show opposite "The Tonight Show". Letterman moved his show to CBS virtually unchanged, taking most of the staff, skits, and comedy formats with him. However, NBC owned the rights to the "Late Night" name, forcing Letterman to rename his show "Late Show with David Letterman".


title: Late Night with Conan O'Brien

text: NBC was not prepared to replace both Letterman and "Late Night". Aside from the name, it needed to build a new show. Both Dana Carvey and Garry Shandling declined to host it. "Saturday Night Live" producer Lorne Michaels was brought in to develop the new show, and comedians Jon Stewart, Drew Carey, and Paul Provenza auditioned to host. Michaels suggested to Conan O'Brien, an unknown writer for "The Simpsons" and former writer for "Saturday Night Live", that he should audition for the job. Despite having "about 40 seconds" of television-performance experience as an occasional extra on "Saturday Night Live" sketches, O'Brien auditioned for the show on April 13, 1993. His guests were Jason Alexander and Mimi Rogers, and the audition took place on the set of "The Tonight Show with Jay Leno". NBC offered the show to O'Brien on April 26, and O'Brien made his first meaningful television appearance later that day when Leno introduced him on "Tonight". On the final episode of his 16-year run, O'Brien stated that he "owed his career to Lorne Michaels."


title: Late Night with Conan O'Brien

text: O'Brien's "Late Night" debuted on September 13, 1993, with Andy Richter chosen as O'Brien's sidekick. The premiere episode featured John Goodman, who received a "First Guest" medal for his appearance, Drew Barrymore, and Tony Randall. The episode featured a cold open of O'Brien's walk to the studio with constant reminders that he was expected to live up to Letterman; meanwhile, Tom Brokaw makes a cameo. After seeming to be unaffected by the comments, O'Brien arrives at his dressing room and cheerfully prepares to hang himself. However, a warning that the show is about to start causes him to abandon his plans.


title: Late Night with Conan O'Brien

text: The show's first musical guest was English rock band Radiohead, who performed during the second episode. American singer-songwriter Jonathan Richman was the show's second musical guest.


title: Late Night with Conan O'Brien

text: O'Brien's inexperience was apparent, and the show was generally considered mediocre by critics in terms of hosting. The "Chicago Sun-Times" Lon Grankhe called O'Brien "nervous, unprepared and generally geeky", and Tom Shales wrote "As for O'Brien, the young man is a living collage of annoying nervous habits. He giggles and titters, jiggles about and fiddles with his cuffs. He has dark, beady little eyes like a rabbit. He's one of the whitest white men ever." (O'Brien wrote for "The New York Times" a satirical review of the first episode the day it aired titled "O'Brien Flops!", in which he told readers "Frankly, I was not impressed".) The originality and quality of the comedy, however, led by original head writer Robert Smigel, was widely praised. Although O'Brien benefited by comparison from the quick critical and commercial failure of the fellow new late-night "The Chevy Chase Show", NBC only offered short-term contracts, 13 weeks at a time and once for six weeks, as widely reported by the press at the time. O'Brien was reportedly almost fired at least once in this period, but NBC had no one to replace him. According to Smigel, "We were basically canceled at "Conan", and then they changed their minds in August of '94, gave us a reprieve."


title: Late Night with Conan O'Brien

text: One NBC affiliate, KPRC-TV in Houston, dropped "Late Night with Conan O'Brien" in September 1994 due to low ratings and was replaced with first-run episodes of "The Jenny Jones Show". KPRC reinstated O'Brien's "Late Night" in the fall of 1996, but scheduled it to air as late as 2:40 a.m. while the station, in addition to "The Jenny Jones Show", had aired "Extra", "Access Hollywood", "Ricki Lake", "Montel Williams", "Inside Edition" and a rebroadcast of its 10:00 p.m. newscast between Leno and O'Brien. Houston became the subject of a skit (via classic remote piece) in which O'Brien made impromptu stops at Houston's central bus terminal and the Astrodome to watch an episode of his own show with Houstonians in 1997. KPRC began airing "Late Night with Conan O'Brien" directly following "The Tonight Show with Jay Leno" in 2004.


title: Late Night with Conan O'Brien

text: According to O'Brien, NBC network executive Warren Littlefield told him, with regard to Andy Richter, he'd "never succeed until I 'got rid of that big fat dildo.' That was the tone of the conversations between us and the network." It was widely expected that the host of "Talk Soup", Greg Kinnear would take over the role, but Kinnear turned down the opportunity. (Kinnear would instead become host of "Late Night"s then-lead-out program, "Later", in February 1994, remaining there for two years before deciding to pursue an acting career.) Stars like Tom Hanks agreed to appear on "Late Night", which boosted audience awareness. Even Letterman, who admired O'Brien's comic sensibility, appeared as a guest to register his support. O'Brien's performance style improved through experience, and he began to receive more favorable reviews and ratings the following year. With the ratings gradually improving over the course of two years, "Late Night" reached a new level of critical and commercial success in 1996. Tom Shales officially recanted his previous critical review with the headline "I was wrong", and O'Brien received his first Emmy nomination for writing, which he received every year until 2011.


title: Late Night with Conan O'Brien

text: In 2000, Richter left "Late Night" on good terms, to pursue his acting career, a move that emotionally affected O'Brien, as evidenced by Richter's last show. The show's comedy bits and banter had usually depended on O'Brien's interaction with Richter. O'Brien's wacky non-sequitur comedy became more pronounced as he played all of his comedy and commentary directly to the audience and Max Weinberg instead of towards Richter.


title: Late Night with Conan O'Brien

text: In 2002, when time came to renew his contract, O'Brien had notable offers from other networks to defect; Fox was reported to have made particularly strong overtures, pitching him an 11:00 p.m. show. O'Brien decided to re-sign with NBC, however, joking that he initially wanted to make a 13-week deal (a nod to his first contract). He ultimately signed through 2005, indicating that it was symbolic of surpassing Letterman's run with 12 years of hosting.


title: Late Night with Conan O'Brien

text: In 2003, O'Brien's own production company, Conaco, was added as a producer of "Late Night". The show celebrated its 10th anniversary, another milestone that O'Brien said he wanted to achieve with his 2002 contract. During the anniversary show, Mr. T handed O'Brien a chain with a large gold "7" on it.


title: Late Night with Conan O'Brien

text: O'Brien's last season on "Late Night" attracted an average of 1.98 million viewers, compared to 1.92 million viewers for "The Late Late Show with Craig Ferguson".


title: Late Night with Conan O'Brien

text: The show was known for its wacky and absurd sophomoric comedic sensibility that is edgier than most other talk shows. Like his "Late Night" predecessor, David Letterman, the show's humor also had a streak of biting sarcasm and irony. According to Robert Smigel, who served as head writer in 1993, the show's comedic approach was to focus on being different from David Letterman:


title: Late Night with Conan O'Brien

text: Typically O'Brien would play the 'straight man' role to the general absurdity of the comedy, treating the material or wacky nature of the sketches with sincerity. The show had an unusual quantity of comedy and original content rather than other talk shows such as "Late Show with David Letterman" or "The Tonight Show with Jay Leno" that relied heavily on recurring segments and 'found' humor. The show was particularly unique in the lack of 'found' humor to derive content from i.e. most content being scripted as opposed to Letterman's Small Town News or Jay Leno's headlines that used this "found humor". O'Brien would often playfully chide his audience for an underwhelming or overly enthusiastic response to his jokes.


title: Late Night with Conan O'Brien

text: Particularly in the early years, comedic sketches overtook all segments on the show, occasionally even interrupting guest interviews and O'Brien's monologue. Frequently sketches would randomly begin without introduction, such as during banter between Richter and O'Brien. A lot of the humor had a fantasy-like quality to it, where inanimate objects would talk or silly characters would disrupt the show. Sometimes a short story would emerge in these sketches with a resolution culminating in a song.


title: Late Night with Conan O'Brien

text: One recurring technique is to superimpose lips onto an existing image, as in the Syncro-Vox limited animation technique, resulting in the speaker saying things often quite out of character.


title: Late Night with Conan O'Brien

text: Although "Late Night" used political humor, it did so far less frequently than competing shows did. During the 1996 and 2000 presidential election seasons, "Late Night" was found to be the least politically-oriented late night program. It averaged 310 political jokes per election season, in contrast to the Leno-led "Tonight Show" with 1,275.


title: Late Night with Conan O'Brien

text: The show's house band was The Max Weinberg 7, led by drummer Max Weinberg. The other six members were Mark Pender on trumpet, Richie "LaBamba" Rosenberg on trombone, Mike Merritt on bass, Jerry Vivino on saxophone and brother Jimmy Vivino on guitar, and Scott Healy on keyboards. Weinberg sometimes took extended leaves of absence to tour with Bruce Springsteen as the drummer for the E Street Band. During his absence, James Wormworth would typically fill in on drums, and the band was led by Vivino under the name Jimmy Vivino and the Max Weinberg 7.


title: Late Night with Conan O'Brien

text: With the departure of Andy Richter from "Late Night" in May 2000, Max Weinberg assumed a bigger role as an interlocutor for O'Brien's jokes. One common running gag was Max's awkwardness on camera and his apparent lack of chemistry with Conan. Weinberg was often used in sketches as well, which usually revolved around his purported sexual deviance (mostly a penchant for bedding barely legal groupies), although long-running sketches also spoofed Max's lack of knowledge of current affairs.


title: Late Night with Conan O'Brien

text: "LaBamba" was also used as the butt of many of Conan's jokes. These humorous sketches usually revolved around LaBamba's sizeable mustache, his poor acting skills, and his alleged inability to read written music. Mark Pender would often sing songs on the topic of a current event which ended with him screeching uncontrollably and climbing the risers into the audience. All members of the 7 have had successful side careers as studio musicians.


title: Late Night with Conan O'Brien

text: The show's opening theme was co-written by composer Howard Shore and John Lurie (of the band The Lounge Lizards). Lurie would later say that he was contracted by Shore to write the theme, and after he turned in the piece, Shore made minimal changes and claimed an unwarranted co-writing credit. Lurie also claimed to have been a finalist for "Late Night"'s band leader position, but said producers told him, "Conan thinks you’re funnier than him and that scares him."


title: Late Night with Conan O'Brien

text: As is common in the talk show format, the Max Weinberg 7 performed the show's opening and closing themes, played bumpers into and out of commercial breaks (they actually played through the entire break for the studio audience), and a short piece during O'Brien's crossover to his desk after his monologue. The show's closing theme was called "Cornell Knowledge", and was lifted from Jerry and Jimmy Vivino's first album together. However, on "Late Night", it was played at a much quicker tempo than the album version. The band also played a wide variety of songs as bumpers coming to and from commercial breaks and introducing guests—usually popular music from a variety of eras.


title: Late Night with Conan O'Brien

text: Joel Godard, a long-time announcer for NBC shows, was the program's announcer and a frequent comedy contributor. On the show's final episode, Conan noted that Godard was originally hired to simply announce the show's intro and claimed "nobody thought you'd ever see him", however he was gradually worked into the show's comedy pieces. These bits usually revolved around Godard's supposed homosexual fetishes, deviant sexual habits, substance abuse, and suicidal tendencies. The humor came in part from Godard's delivery. No matter how depressing or deviant the topic being discussed was, he always did so in an exaggeratedly cheerful voice and with a huge smile plastered on his face. Several sketches ended with Godard apparently committing suicide in his announcer's booth.


title: Late Night with Conan O'Brien

text: In the first few seasons of the show, the writing staff consisted of several now-prolific comics including Robert Smigel as the head writer, Bob Odenkirk, Louis C.K., Tommy Blacha and Dino Stamatopoulos. Smigel left his position as head writer of the show in 1995 to pen several movies but continued to appear on the show to do bits as Triumph the Insult Comic Dog and the 'Satellite Interviews'. Jonathan Groff took over his position until replaced by Mike Sweeney in 2001.


title: Late Night with Conan O'Brien

text: Members of the show's writing staff frequently appeared in sketches on the show. Among the most prolific were: Brian McCann (Preparation H Raymond, FedEx Pope, The Loser, Airsick Moth, Jerry Butters, Awesome Dave, Funhole Guy, Bulletproof Legs Guy, Adrian "Raisin" Foster, S&M Lincoln, etc.), Brian Stack (Hannigan the Traveling Salesman, Artie Kendall the Ghost Crooner, The Interrupter, Kilty McBagpipes, Fan-tastic Guy, Clive Clemmons, Frankenstein, Ira, Slipnut Brian, etc.), Jon Glaser (Segue Sam, Pubes, Awareness Del, Wrist Hulk, Ahole Ronald, Gorton's Fisherman, Jeremy, Slipnut Jon, etc.), Kevin Dorff (Coked-up Werewolf, Jesus Christ, Mansy the half-man/half-pansy, Joe's Bartender, Todd the Tiny Guy, etc.), and Andy Blitz (Awful Ballgame Chanter, Vin Diesel's brother Leonard Diesel, Slipnut Andy, Chuck Aloo aka the star of the "24" spin-off series "60"). Blitz went so far as to travel to India for one bit in which he carried his computer through the streets of India to get technical support firsthand from the telephone representative at NBC's technical help center.


title: Late Night with Conan O'Brien

text: Several writing staff interns have gone on to become noted actors or writers including Vanessa Bayer, John Krasinski, Mindy Kaling, Ellie Kemper and Jack McBrayer.


title: Late Night with Conan O'Brien

text: "Late Night" employed a number of sketch actors, many of whom were frequently reused in different roles in different episodes. Several years before joining the cast of "Saturday Night Live", and before playing the role of Leslie Knope on another NBC TV show, "Parks and Recreation", Amy Poehler often appeared as a regular in many sketches, though she was best remembered for playing the recurring role of Andy Richter's Conan-obsessed teenage sister, Stacy. Other notable comedians such as Jack McBrayer, Rob Riggle, Rob Corddry, H. Jon Benjamin, Ellie Kemper, Bobby Moynihan, Matt Besser, Ian Roberts, Matt Walsh and Andrew Daly also frequently appeared as sketch actors on the show for several years. Triumph the Insult Comic Dog (created and voiced by original head writer Robert Smigel) began as part of a sketch on "Late Night." Celebrities such as Dr. Joyce Brothers, Nipsey Russell, Abe Vigoda, James Lipton, Bob Saget and William Preston as the character Carl 'Oldy' Olsen also made frequent cameo appearances in comedy sketches on the show at different periods. One of the show's graphic designers, Pierre Bernard, was featured in several sketches, such as "Pierre Bernard's Recliner of Rage" and "Nerding It Up For Pierre".


title: Late Night with Conan O'Brien

text: Celebrity guests of the night would also occasionally appear in sketches either during their interviews or during the earlier comedy segments, e.g. in "In the year 2000" (which always included the participation of a celebrity guest after Andy Richter left the show) or a sketch where Conan would pretend to write in his diary while an attractive female guest was there. Quite rare for a talk show, sometimes interviews began normally but turned into sketches with both the guest and Conan participating, usually when the guest was a "friend of the show."


title: Late Night with Conan O'Brien

text: Unusual for a late night talk show, "Late Night" made frequent use of various costumed characters such as The Masturbating Bear, Robot on a Toilet, and Pimpbot 5000. The humor in these sketches often derived from the crude construction of the characters' costumes as well as the absurdist nature of their conceptions. For example, Pimpbot 5000 was a 1950s-style robot who dressed and acted in the manner of an exaggerated blaxploitation pimp, while The Masturbating Bear was a man in a bear costume wearing an oversized diaper who would invariably begin to fondle himself to the tune of Aram Khachaturian's "Sabre Dance" when brought on stage. Many of these characters did little more in their appearances than walk across the stage or be wheeled out from behind the curtain, but some had extensive sketches on the show.


title: Late Night with Conan O'Brien

text: The show made a cameo appearance in the "Sesame Street" special "Elmopalooza", where Conan was interviewing two aliens while Big Bird was passing by them carrying a video tape.


title: Late Night with Conan O'Brien

text: The show also made an appearance on "The Simpsons" in the episode "Bart Gets Famous", where Conan interviews a now famous Bart.


title: Late Night with Conan O'Brien

text: "Late Night" was a production of Lorne Michaels's Broadway Video (and, since 2003, O'Brien's Conaco). It was taped in Studio 6A in the GE Building at 30 Rockefeller Plaza in New York City. Next to the door were framed pictures of Letterman, Carson, Jack Paar and Steve Allen, each of whose groundbreaking late-night shows originated from studio 6A or 6B (where "The Tonight Show Starring Jimmy Fallon" is currently taped). The studio holds just over 200 audience members. It was taped at about 5:30 pm as an uninterrupted hour-long program, with the band playing music through the portions that would be filled by commercials. Generally, shows were taped at 5:30 pm Monday through Friday, although for much of the show's run, reruns would be aired on Mondays and the show would not tape that day.


title: Late Night with Conan O'Brien

text: The show's format consisted of an opening monologue from O'Brien, followed by various "desk bits". These generally included several brief sketches, recurring segments, or some other form of comedy. Typically O'Brien would play the 'straight man' role to the general absurdity of the comedy, treating the material or wacky nature of the sketches with sincerity. In the show's second and fourth segments, O'Brien interviewed two celebrity guests, between which, in the third segment, O'Brien listed the next night's/week's guests. There was often a comedy bit as well during this segment. The show's fifth segment was usually reserved for a musical or stand-up comedy performance, or occasionally another guest interview. The show's final segment was usually a quick "goodnight" and the closing credits, which sometimes featured part of a bit from earlier in the show. Quite rare for a talkshow, frequently comedy segments would also spill into the interviews, typically when a guest was a 'friend'of the show.