Substances and Mixtures About Watch and Favorite Watch Watching this resources will notify you when proposed changes or new versions are created so you can keep track of improvements that have been made. Favorite Favoriting this resource allows you to save it in the “My Resources” tab of your account. There, you can easily access this resource later when you’re ready to customize it or assign it to your students. Substances and Mixtures Substances are composed of pure elements or chemically bonded elements, whereas mixtures are composed of non-bonded substances. Learning Objective Distinguish chemical substances from mixtures Key Points Matter can be broken down into two categories: pure substances and mixtures . Pure substances are further broken down into elements and compounds . Mixtures are physically combined structures that can be separated into their original components. A chemical substance is composed of one type of atom or molecule . A mixture is composed of different types of atoms or molecules that are not chemically bonded. A heterogeneous mixture is a mixture of two or more chemical substances where the various components can be visually distinguished. A homogeneous mixture is a type of mixture in which the composition is uniform and every part of the solution has the same properties.

Various separation techniques exist in order to separate matter, including include distillation, filtration, evaporation and chromatography. Matter can be in the same phase or in two different phases for this separation to take place. Terms Full Text Chemical Substances In chemistry , a chemical substance is a form of matter that has constant chemical composition and characteristic properties. It cannot be separated into components without breaking chemical bonds . Chemical substances can be solids , liquids , gases, or plasma . Changes in temperature or pressure can cause substances to shift between the different phases of matter. An element is a chemical substance that is made up of a particular kind of atom and hence cannot be broken down or transformed by a chemical reaction into a different element. All atoms of an element have the same number of protons , though they may have different numbers of neutrons and electrons . A pure chemical compound is a chemical substance that is composed of a particular set of molecules or ions that are chemically bonded. Two or more elements combined into one substance through a chemical reaction, such as water, form a chemical compound. All compounds are substances, but not all substances are compounds. A chemical compound can be either atoms bonded together in molecules or crystals in which atoms, molecules or ions form a crystalline lattice .

Compounds made primarily of carbon and hydrogen atoms are called organic compounds, and all others are called inorganic compounds. Compounds containing bonds between carbon and a metal are called organometallic compounds. Chemical substances are often called 'pure' to set them apart from mixtures. A common example of a chemical substance is pure water; it always has the same properties and the same ratio of hydrogen to oxygen whether it is isolated from a river or made in a laboratory. Other chemical substances commonly encountered in pure form are diamond (carbon), gold, table salt (sodium chloride), and refined sugar (sucrose). Simple or seemingly pure substances found in nature can in fact be mixtures of chemical substances. For example, tap water may contain small amounts of dissolved sodium chloride and compounds containing iron, calcium, and many other chemical substances. Pure distilled water is a substance, but seawater, since it contains ions and complex molecules, is a mixture. Chemical Mixtures A mixture is a material system made up of two or more different substances, which are mixed but not combined chemically. A mixture refers to the physical combination of two or more substances in which the identities of the individual substances are retained.

Mixtures take the form of alloys , solutions, suspensions, and colloids . What are some examples of homogeneous mixtures and heterogeneous mixtures? | eNotes What are some examples of homogeneous mixtures and heterogeneous mixtures? melony82 | High School Teacher | (Level 1) Associate Educator Posted on November 7, 2008 at 12:51 AM A compound is a chemical combination of two or more elements in definite proportions. For example, two hydrogen molecules + one oxygen molecule= one water molecule. A solution is a physical combination of two or more chemicals mixed evenly (salt that is dissolved in water). Solutions are also known as homogenous mixtures. A mechanical mixture is a physical combination of two or more chemicals that are not evenly mixed (hot fudge on ice cream). Mechanical mixtures are also known as heterogenous mixtures. Examples: Homogenous: milk, kool-aid, blood, lotion, window cleaner, glue, etc. Heterogenous: pizza, cereal and milk, rocks in the sand at the beach, banana splits, etc.

like 30 dislike 2 ksssy | High School Teacher | (Level 1) Adjunct Educator Posted on Homogeneous mixuters are those in which the components are evenly distributed over the major component/constitute of the mixture. Eg: blood, milk. Hetrogeneous mixtures are mixtures are those in which the components are not evenly distributed over the major component/constitute of the mixture. The very (unevenly distributed) form of heterogeneous mixtures is the reason why most people shake the mixtures before using them. Eg: Milk of Magnesia, Copper Sulphate sciftw | High School Teacher | (Level 1) Educator Emeritus Posted on October 12, 2015 at 1:32 PM A homogeneous mixture and a heterogeneous mixture are first and foremost both mixtures. That means no chemical bonding has occurred between the substances within the mixtures. They can be separated through physical means if necessary. The difference between the two mixtures is in how well they are mixed. Heterogeneous mixtures are mixtures that are not well mixed. A person could see the individual pieces that are mixed together.

Foods are often great examples of heterogeneous mixtures. For example, a fruit salad is a heterogeneous mixture. So is trail mix and Lucky Charms. Pepper works too, because you can see all of the different pieces that make up pepper. A homogeneous mixture is a mixture that is really well mixed. It's so well mixed that you can't see the different parts of the mixture. It all looks uniform. The air that you are breathing right now is a homogeneous mixture. It's made up of several different gasses that are so thoroughly mixed together that they appear uniform. Milk is also a homogeneous mixture. It looks uniform throughout. In fact, if you have a gallon of milk in your refrigerator at home, go check the container. It more than likely says "homogenized." Sources: Mixtures In Depth Tutorials and Information Mixtures CONCEPT Elements and compounds are pure substances, but much of the material around us—including air, wood, soil, and even (in most cases) water— appears in the form of a mixture. Unlike a pure substance, a mixture has variable composition: in other words, it cannot be reduced to a single type of atom or molecule.

Mixtures can be either homogeneous—that is, uniform in appearance, and having only one phase—or heterogeneous, meaning that the mixture is separated into various regions with differing properties. Most homogeneous mixtures are also known as solutions, and examples of these include air, coffee, and even metal alloys. As for heterogeneous mixtures, these occur, for instance, when sand or oil are placed in water. Oil can, however, be dispersed in water as an emulsion, with the aid of a surfactant or emulsifier, and the result is an almost homogeneous mixture. Another interesting example of a heterogeneous mixture occurs when colloids are suspended in fluid, whether that fluid be air or water. HOW IT WORKS Mixtures and Pure Substances A mixture is a substance with a variable composition, meaning that it is composed of molecules or atoms of differing types. These may have intermolecular bonds, or bonds between molecules, but such bonds are not nearly as strong as those formed when elements bond to form a compound. Examples of mixtures include milk, coffee, tea, and soft drinks—indeed, they include virtually any drink except for pure water, which is a rarity, because water is highly soluble and tends to contain minerals and other impurities.

Air, too, is a mixture, because it contains oxygen, nitrogen, noble gases, carbon dioxide, and water vapor. Likewise metal alloys such as bronze, brass, and steel are mixtures. Structural and phenomenological distinctions Before chemists accepted the atomic theory of matter, it was often difficult to distinguish a mixture, such as air or steel, from pure substances, which have the same composition throughout. Pure substances are either elements such as oxygen or iron, or compounds—for example, carbon dioxide or iron oxide. An element is made up of only one type of atom, while a compound can be reduced to one type of bonded chemical species—usually either a molecule or a formation of ions. A distinction between mixtures and pure substances based on atomic and molecular structures is called, fittingly enough, a structural definition. Prior to the development of atomic theory by English chemist John Dalton (1766-1844), and the subsequent identification of molecules by Italian physicist Amedeo Avogadro (17761856), chemists defined compounds and mixtures on the basis of phenomenological data garnered through observation and measurement. This could and did lead to incorrect suppositions.

Proust and the debate over constant composition Around the time of Dalton and Avogadro, French The wondrous invention known as soap is a mixture with surfactant qualities. chemist Antoine Lavoisier (1743-1794) correctly identified an element as a substance that could not be broken down into a simpler substance. Later, his countryman Joseph-Louis Proust (1754-1826) clarified the definition of a compound, stating it in much the same terms that we have used: the composition of a compound is the same throughout. But with the very rudimentary knowledge of atoms and molecules that chemists of the early nineteenth century possessed, the distinctions between compounds and mixtures remained elusive. Proust’s contemporary and intellectual rival Claude Louis Berthollet (1748-1822) observed that when metals such as iron are heated, they form oxides in which the percentage of oxygen increases with temperature. If constant composition is a fact, he challenged Proust, then how is this possible? Proust maintained that the proportions of elements in a compound are always the same, a hypothesis Berthollet countered by observing that metals can form variable alloys.

Bronze, for instance, is an alloy of tin and copper at a ratio of about 25:75, but if the ratio were changed to, say, 30:70, it would still be called bronze. At the time, the equipment—both in terms of knowledge and tools for analysis—simply did not exist whereby Berthollet’s assertions could be successfully proven wrong. Indeed, Berthollet, a student of Lavoisier who contributed to progress in the study of acids and reactants, was no anti-scientific villain: he was simply responding to the evidence as he saw it. Only with the discovery of subatomic particles in the late nineteenth and early twentieth centuries, discoveries that changed the entire character of chemistry as a discipline, did it truly become possible to answer Berthollet’s challenges. Chemists now understand that the oxide formed on the surface of a metal is a compound separate from the metal itself, and that alloys (discussed later in this essay) are not compounds at all: they are mixtures. Mixtures and Compounds With our modern knowledge of atomic and molecular properties, we can more fully distinguish between a compound and a mixture.

First, a mixture can exist in virtually any proportion among its constituent parts, whereas a compound has a definite and constant composition. Coffee, whether weak or strong, is still coffee, but if a second oxygen atom chemically bonds to the oxygen in carbon monoxide (CO), the resulting Bronze—an alloy of tin and copper—was one of the most important inventions in human history. This stone carving is from the period known as the Bronze Age. compound is not simply “strong carbon monoxide” or even “oxygenated carbon monoxide”: it is carbon dioxide (CO2), an entirely different substance. The difference is enormous: carbon dioxide is a part of the interactions between plant and animal life that sustains the natural environment, whereas carbon monoxide is a toxic gas produced, for instance, by automobiles. Second, the parts of a mixture retain most of their properties when they join together, but elements lose their elemental characteristics once they form a compound. Sugar is still sweet, regardless of the substance into which it is dissolved. In coffee or another drink, it may no longer be dry and granular, though it could be returned to that state by evaporating the coffee. In any case, dryness and granularity are physical properties, whereas sweetness is a chemical one.

On the other hand, when elemental carbon bonds with hydrogen and oxygen to form sugar itself, the resulting compound is nothing like the elements from which it is made. Third, a mixture can usually be created simply by the physical act of stirring items together, and/or by applying heat. As discussed below, relatively high temperatures are sometimes needed to dissolve sugar in tea, for instance; likewise, alloys are usually formed by heating metals to much higher temperatures. On the other hand, the formation of a compound involves a chemical reaction, a vastly more complex interaction than the one required to create a mixture. Carbon, a black solid found in coal, can be mixed with hydrogen and oxygen—both colorless and odorless gases—and the resulting mess would be something; but it would not be sugar. Only the chemical reaction between the three elements, in specific proportions and under specific conditions, results in their chemical bonding to form table sugar, known to chemists as sucrose. Homogeneous and Heteroge-neous Mixtures Homogeneous mixtures and solutions As we have seen, the composition of a mixture is variable. Coffee, for instance, can be weak or strong, and milk can be “whole” or low-fat.

Beer can be light or dark in color, as well as “light” in terms of calorie content; furthermore, its alcohol content can be varied, as with all alcoholic drinks. Though their molecular composition is variable, each of the mixtures described here is the same throughout: in other words, there is no difference between one region and another in a glass of beer. Such a mixture is described as homogeneous. A homogeneous mixture is one that is the same throughout, but this is not the same as saying that a compound has a constant composition. Rather, when we say that a homogeneous mixture is the same in every region, we are speaking phenomenologically rather than structurally. From the standpoint of ordinary observation, a glass of milk is uniform, but as we shall see, milk is actually a type of emulsion, in which one substance is dispersed in another. There are no milk “molecules,” and structural analysis would reveal that milk does not have a constant molecular composition. Coffee is an example of a solution, a specific type of homogeneous mixture.

Actually, most homogeneous mixtures can be considered solutions, but since a solution is properly defined as a homogeneous mixture in which one or more substances is dissolved in another substance, a 50:50 homogeneous mixture is technically not a solution. When particles are perfectly dissolved in a solution, the composition is uniform, but again, this is not a compound, because that composition can always be varied. Heterogeneous mixtures Anyone who has ever made iced tea has observed that it is easy to sweeten when it is hot, because temperature affects the ability of a solvent such as water—in this case, water with particles from tea leaves filtered into it—to dissolve a solute, such as sugar. Cold tea, on the other hand, is much harder to sweeten with ordinary sugar. Usually what happens is that, instead of obtaining a homogeneous mixture, the result is heterogeneous. Whereas every region within a homogeneous mixture is more or less the same as every other region, heterogeneous mixtures contain regions that differ from one another.

In the example we have used, a glass of cold tea with undissolved sugar at the bottom is a heterogeneous mixture: the tea at the top is unsweetened or even bitter, whereas at the bottom, there is an overly sweet sludge of tea and sugar. From homogeneous to heterogeneous and back again The distinction between homogeneous and heterogeneous solutions only serves to further highlight the difference between compounds and mixtures. Whereas the composition of a compound is definite and quantitative (so many atoms of element x bonded with so many atoms of element y in such-and-such a structure), there is less of a sharp dividing line between homogeneous and heterogeneous solutions. When too much of a solute is added to the solvent, the solvent becomes saturated, and is no longer truly homogeneous. Such is the case when the sugar drifts to the bottom of the tea, or when coffee grounds form in the bottom of a coffee pot containing an otherwise uniform mixture of coffee and water. Milk comes to us as a homogeneous substance, thanks to the process of homogenization, but when it comes out of the cow, it is a more heterogeneous mixture of milk fat and water.

In fact, milk is an example of an emulsion, the result of a process whereby two substances that would otherwise form a heterogeneous mixture are made to form a homogeneous one. REAL-LIFE APPLICATIONS Colloids In 1827, Scottish naturalist Robert Brown (17731858) was studying pollen grains under a microscope when he noticed that the grains underwent a curious zigzagging motion in the water. At first, he assumed that the motion had a biological explanation—in other words, that it resulted from life processes within the pollen—but later, he discovered that even pollen from long-dead plants behaved in the same way. What Brown had observed was the suspension of a colloid—a particle intermediate in size between a molecule and a speck of dust—in the water. When placed in water or another fluid (both liquids and gases are called “fluids” in the physical sciences), a colloid forms a mixture similar both to a solution and a suspension. As with a solution, the composition remains homoge-neous—the particles never settle to the bottom of the container. At the same time, however, the particles remain suspended rather than dissolved, rendering a cloudy appearance to the dispersion.

Almost everyone, especially as a child, has been fascinated by the colloidal dispersion of dust particles in a beam of sunlight. They seem to be continually in motion, as indeed they are, and this movement is called “Brownian motion” in honor of the man who first observed it. Yet Brown did not understand what he was seeing; only later did scientists recognize that Brownian motion is the result of movement on the part of molecules in a fluid. Even though the molecules are much smaller than the colloid, there are enough of them producing enough collisions to cause the colloid to be in constant motion. Another remarkable aspect of dust particles floating in sunlight is the way that they cause a column of sunlight to become visible. This phenomenon, called the Tyndall effect after English physicist John Tyndall (1820-1893), makes it seem as though we are actually seeing a beam of light. In fact, what we are seeing is the reflection of light off the colloidal dispersion. Another example of a colloidal dispersion occurs when a puff of smoke hangs in the air; furthermore, as we shall see, milk is a substance made up of colloids—in this case, particles of fat and protein suspended in water.

Emulsions Miscibility is a qualitative term identifying the relative ability of two substances to dissolve in one another. Generally, water and water-based substances have high miscibility with regard to one another, as do oil and oil-based substances with one another. Oil and water, on the other hand (or substances based in either) have very low miscibility. The reason is that water molecules are polar, meaning that the positive electric charge is in one region of the molecule, while the negative charge is in another region. Oil, on the other hand, is nonpolar, meaning that charges are more evenly distributed throughout the molecule. Trying to mix oil and water is thus rather like attempting to use a magnet to attract a nonmagnetic metal such as gold. How surfactants aid the emulsion process An emulsion is a mixture of two immiscible liquids such as oil and water—we will use these simple terms, with the idea that these stand for all oil- and water-soluble substances—by dispersing microscopic droplets of one liquid in another. In order to achieve this dispersion, there needs to be a “middle man,” known as an emulsifier or surfactant.

The surfactant, made up of molecules that are both water- and oil-soluble, acts as an agent for joining other substances in an emulsion. All liquids have a certain degree of surface tension. This is what causes water on a hard surface to bead up instead of lying flat. (Mercury has an extremely high surface tension.) Surfactants break down this surface tension, enabling the marriage of two formerly immiscible liquids. In an emulsion, millions of surfactants surround the dispersed droplets (known as the internal phase), shielding them from the other liquid (the external phase). Supposing oil is the internal phase, then the oil-soluble end of the surfactant points toward the oils, while the water-soluble side joins with the water of the external phase. Physical characteristics of an emulsion The resulting emulsion has physical (as opposed to chemical) properties different from those of the substances that make it up. Water and most oils are transparent, whereas emulsions are typically opaque and may have a lustrous, pearly gleam. Oil and water flow freely, but emulsions can be made to form thick, non-flowing creams.

Emulsions are inherently unstable: they are, as it were, only temporarily homogeneous. A good example of this is an oil-and-vinegar salad dressing, which has to be shaken before putting it on salad; otherwise, what comes out of the bottle is likely to be mainly oil, which floats to the top of the water-based vinegar. It is characteristic of emulsions that eventually gravity pulls them apart, so that the lighter substances float to the top. This process may take only a few minutes, as with the salad dressing; on the other hand, it can take thousands of years. Applications Surfactants themselves are often used in laundry or dish detergent, because most stains on plates or clothes are oil-based, whereas the detergent itself is applied to the clothes in an aqueous solution. As for emulsions, these are found in a wide variety of products, from cosmetics to paint to milk. In the pharmaceutical industry, for instance, emulsions are used as a means of delivering the active ingredients of drugs, many of which are not water soluble, in a medium that is.

Pharmaceutical manufacturers also use emulsions to make medicines more palatable (easier to take); to control dosage and improve effectiveness; and to improve the usefulness of topical drugs such as ointments, which must contend with both oily and water-soluble substances on the skin. The oils and other conditioning agents used in hair-care products would leave hair limp and sticky if applied by themselves. Instead, these products are applied in emulsions that dilute the oils in other materials. Emulsions are also used in color photography, as well as in the production of pesticides and fungicides. Paints and inks, too, are typically emulsified substances, and these sometimes come in the form of dispersions akin to those of colloids. As we have seen, in a dispersion fine particles of solids are suspended in a liquid. Surfactants are used to bond the particles to the liquid, though paint must be shaken, usually with the aid of a high-speed machine, before it is consistent enough to apply. As mentioned earlier, milk is a form of emulsion that contains particles of milk fat or cream dispersed in water. Light strikes the microscopic fat and protein colloids, resulting in the familiar white color.

Other examples of emulsified foods include not only salad dressings, but gravies and various sauces, peanut butter, ice cream, and other items. Not only does emulsion affect the physical properties of foods, but it may enhance the taste by coating the tongue with emulsified oils. Soap The wondrous invention called soap, which has made the world a cleaner place, exhibits several of the properties we have discussed. It is a mixture with surfactant qualities, and in powdered form, it can form something close to a true solution with water. Discovered probably by the Phoenicians around 600 B.C., it was made in ancient times by boiling animal fat (tallow) or vegetable oils with an alkali or base of wood ashes. This was a costly process, and for many centuries, only the wealthy could afford soap—a fact that contributed to the notorious lack of personal hygiene that prevailed among Europeans of the Middle Ages. In fact, the situation did not change until late in the eighteenth century, when the work of two French chemists yielded a more economical manufacturing method.

In 1790, Nicholas Leblanc (1742-1806) developed a process for creating sodium hydroxide (called caustic soda at the time) from sodium chloride, or ordinary table salt. This made for an inexpensive base or alkali, with which soap manufacturers could combine natural fats and oils. Then in 1823, Michel Eugene Chevreul (17861889) showed that fat is a compound of glycerol with organic acids, a breakthrough that led to the use of fatty acids in producing soaps. The chemistry of soap Soap as it is made today comes from a salt of an alkali metal, such as sodium or potassium, combined with a mixture of carboxylic acids (“fatty acids”). These carboxylic acids are the result of a reaction called saponification, involving triglyc-erides and a base, such as sodium hydroxide. Saponification breaks the triglycerides into their component fatty acids; then, the base neutralizes these to salts. This reaction produces glycerin, a hydrocarbon bonded to a hydroxyl (-OH) group.

(Hydrocarbons are discussed in the essays on Organic Chemistry; Polymers.) In general, the formula for soap is RCOOX, where X stands for the alkali metals, and R for the hydrocarbon chain. Because it is a salt (meaning that it is formed from the reaction of an acid with a base), soap partially separates into its component ions in water. The active ion is RCOO-, whose two ends behave in different fashions, making it a surfactant. The hydrocarbon end (R-) is said to be lipophilic, or “oil-loving,” which is appropriate, since most oils are hydrocarbons. On the other hand, the carboxylate end (-COO-) is hydrophilic, or “water-loving.” As a result, soap can dissolve in water, but can also clean greasy stains. When soap is mixed with water, it does not form a true homogeneous mixture or solution due to the presence of hydrocarbons. These attract one another, forming spherical aggregates called micelles. The lipophilic “tails” of the hydrocarbons are turned toward the interior of the micelle, while the hydrophilic heads remain facing toward the water that forms the external phase.

Alloys We have primarily discussed liquid mixtures, but in fact mixtures can be gaseous or even solid—as for example in the case of an alloy, a mixture of two or more metals. Alloys are usually created by melting the component metals, then mixing them together in specific proportions, but an alloy can also be created by bonding metal powders. The structure of an elemental metal includes tight “electron sea” bonds, which are discussed in the essay on Metals. These, combined with the metal’s crystalline structure, create a situation in which internal bonding is very strong, but nondirectional. As a result, most metals form alloys, but again, this is not the same as a compound: the elemental metals retain their identity in these metal composites, forming characteristic fibers, beads, and other shapes. KEY TERMS Alloy: A mixture of two or more metals. Aqueous: A term describing a solution in which a substance or substances are dissolved in water. Atom: The smallest particle of an element. Chemical species: A generic term used for any substance studied in chemistry—whether it be an element, compound, mixture, atom, molecule, ion, and so forth.

Compound: A substance made up of atoms of more than one element, which are chemically bonded and usually joined in molecules. The composition of a compound is always the same, unless it is changed chemically. Dispersion: A term describing the distribution of particles in a fluid. Element: A substance made up of only one kind of atom. Unlike compounds, elements cannot be chemically broken down into other substances. Emulsifier: A surfactant. Emulsion: A mixture of two immiscible liquids such as oil and water, made by dispersing microscopic droplets of one liquid in another. In creating an emulsion, surfactants act as bridges between the two liquids. Fluid: A substance with the ability to flow. In physical sciences such as chemistry and physics, “fluid” refers both to liquids and gases. Heterogeneous: A term describing a mixture that is not the same throughout; rather, it has various regions possessing different properties. An example of a mixture is sand in a container of water. Rather than dissolving to form a homogeneous mixture, as sugar would, the sand sinks to the bottom. Homogeneous: A term describing a mixture that is the same throughout, as for example when sugar is fully dissolved in water.

A solution is a homogenous mixture. Immiscible: Possessing a negligible value of miscibility. Ion: An atom or group of atoms that has lost or gained one or more electrons, and thus has a net electric charge. Miscibility: A qualitative term identifying the relative ability of two substances to dissolve in one another. Mixture: A substance with a variable composition, meaning that it is composed of molecules or atoms of differing types. Compare with pure substance or compound. Molecule: A group of atoms, usually but not always representing more than one element, joined in a structure. Compounds are typically made of up molecules. Phenomenological: A term describing scientific definitions based purely on experimental phenomena. These only convey part of the picture, however— primarily, the part a chemist can perceive either through measurement or through the senses, such as sight. A structural definition is therefore usually preferable to a phenomenological one. Pure substance: A substance that has the same composition throughout. Pure substances are either elements or compounds, and should not be confused with mixtures. A homogeneous mixture is not the same as a pure substance, because although it has an unvarying composition, it cannot be reduced to a single type of atom or molecule.

Solution: A homogeneous mixture in which one or more substances is dissolved in another substances—for example, sugar dissolved in water. Structural: A term describing scientific definitions based on aspects of molecular structure rather than purely phenomenological data. Surfactant: A substance made up of molecules that are both water- and oil-soluble, which acts as an agent for joining other substances in an emulsion. Suspension: A term that refers to a mixture in which solid particles are suspended in a fluid. Some famous alloys One of the most important alloys in early human history was a 25:75 mixture of tin and copper that gave its name to an entire stage of technological development: the Bronze Age (c. 3300-1200 B.C.). This combination formed a metal much stronger than either copper or tin, and bronze remained dominant until the discovery of new iron-smelting methods ushered in the Iron Age in about 1200 B.C. Another important alloy of the ancient world was brass, which is about one-third zinc to two-thirds copper. Introduced in the period c. 1400-c. 1200 B.C, brass was one of the metals that defined the world in which the Bible was written.

Biblical references to it abound, as in the famous passage from I Corinthians 13 (read at many weddings), in which the Apostle Paul proclaims that “without love, I am as sounding brass.” Some biblical scholars, however, maintain that some of the references to brass in the Old Testament are actually mistranslations of “bronze.” Tin, copper, and antimony form pewter, a soft mixture that can be molded when cold and beaten regularly without turning brittle. Though used in Roman times, it became most popular in England from the fourteenth to the eighteenth centuries, when it offered a cheap substitute for silver in plates, cups, candelabra, and pitchers. The pewter turned out by colonial American metalsmiths is still admired for its beauty and functionality. As for iron, it appears in nature as an impure ore, but even when purified, it is typically alloyed with other elements. Among the well-known forms of iron are cast iron, a variety of mixtures containing carbon and/or silicon; wrought iron, which contains small amounts of various other elements, such as nickel, cobalt, copper, chromium, and molybdenum; and steel.

Steel is a mixture of iron with manganese and chromium, purified with a blast of hot air. Steel is also sometimes alloyed with aluminum in a one-third/two-thirds mixture to make duraluminum, developed for the superstructures of German zeppelins during World War I. Introductory Chemistry Online/Physical and Chemical Properties of Matter - Wikibooks, open books for an open world Introductory Chemistry Online/Physical and Chemical Properties of Matter From Wikibooks, open books for an open world 7 Supplementary Problems 2.1 Pure Substances and Mixtures[ edit ] In Chapter 1, we learned that atoms are composed of electrons, protons and neutrons and that the number of protons in the nucleus of an atom (the atomic number) defines the identity of that element. For example, an atom with six protons in its nucleus is a carbon atom; seven protons makes it nitrogen; eight protons makes it oxygen, and so on. The periodic table organizes these elements by atomic number and there are currently over 116 known elements.

Because there are clearly more than 116 different types of substances in the world around us, we can see that most substances that we encounter are not pure elements, but are composed of different elements combined together. In chemistry, we refer to these as compounds, which we define as a substance that results from the combination of two or more elements in a constant ratio. For example, water is a compound composed of two hydrogen atoms bonded to one oxygen atom. We can show the ratio of hydrogen to oxygen in this compound by using subscripts on the chemical symbols for each element. Thus, water (two hydrogens and one oxygen) can be written as H2O. This shorthand notation for water is called a chemical formula. For any compound, the chemical formula tells us the elements that are present and the ratio of the elements to each other. Later we will see that water is a member of a special sub-type of compound, called a molecular compound. In a molecule, the atoms are not only bonded together in a constant ratio, but they are bonded in a specific geometric arrangement as well (Figure 2.1) .

In the following chapter, we will look more closely at how elements are bonded together in compounds, but first we will examine some of the properties of chemical substances. When we speak of a pure substance, we are speaking of something that contains only one kind of matter. This can either be one single element or one single compound, but every sample of this substance that you examine must contain exactly the same thing with a fixed, definite set of properties. If we take two or more pure substances and mix them together, we refer to this as a mixture. Mixtures can always be separated again into component pure substances,because bonding among the atoms of the constituent substances does not occur in a mixture. Whereas a compound may have very different properties from the elements that compose it, in mixtures the substances keep their individual properties. For example sodium is a soft shiny metal and chlorine is a pungent green gas. These two elements can combine to form the compound, sodium chloride (table salt) which is a white, crystalline solid having none of the properties of either sodium or chlorine.

If, however, you mixed table salt with ground pepper, you would still be able to see the individual grains of each of them and, if you were patient, you could take tweezers and carefully separate them back into pure salt and pure pepper. (Figure 2.2) Mixtures fall into two types, based on the uniformity of their composition. The first, called a heterogeneous mixture, is distinguished by the fact that different samples of the mixture may have a different composition. For example, if you open a container of mixed nuts and pull out a series of small samples and examine them, the exact ratio of peanuts-to-almonds in the samples will always be slightly different, no matter how carefully you mix them. Common examples of heterogeneous mixtures include dirt, gravel and vegetable soup. (Figure 2.3) In a homogeneous mixture, on the other hand, any sample that you examine will have exactly the same composition as any other sample. Within chemistry, the most common type of homogeneous mixture is a solution which is one substance dissolved completely within another. Think of a solution of pure sugar dissolved in pure water (Figure 2.4) .

Any sample of the solution that you examine will have exactly the same ratio of sugar-to-water, which means that it is a homogeneous mixture. Even in a homogeneous mixture, the properties of the components are generally recognizable. Thus, sugar-water tastes sweet (like sugar) and is wet (like water). Unlike a compound, which has a fixed, definite ratio, in a mixture one can vary the amounts of each component. For example, when you add a little sugar to one cup of tea and a lot of sugar to another, each cup will contain a homogeneous mixture of tea and sugar but they will have a different taste. If you add so much sugar that some does not dissolve and stays on the bottom, however, the mixture is no longer homogeneous, it is heterogeneous;you could easily separate the two components. Exercise 2.1 Distinguishing Substances & Mixtures 2.2 The States of Matter[ edit ] As described in Section 2.1, a molecule of water is composed of two atoms of hydrogen bonded to one atom of oxygen(H2O). All water molecules are exactly the same (same ratio of elements, same geometric bonding pattern), but we encounter water in three different forms in the world around us.

At low temperature, water exists as a solid (ice). As the temperature increases, water exists as a liquid, and at high temperature, as water vapor, a gas. An example in which these three states (or phases) exist simultaneously is shown in Figure 2.5 . These three forms of water represent the three states of matter: solids, liquids and gases. States of matter are examples of physical properties of a substance. Other physical properties include appearance (shiny, dull, smooth, rough), odor, electrical conductivity, thermal conductivity, hardness and density, to name just a few. We will discuss density in more detail in the next section, but first let’s examine the states of matter and how they differ on an atomic level. If ice, liquid water and water vapor all consist of identical molecules, then what accounts for the difference in their properties? So far, we have talked about molecules as if they were standing still, but in fact, they are always moving. In chemistry, we often explain the states of matter in terms of the kinetic molecular theory (KMT). The word kinetic refers to motion and the kinetic molecular theory suggests that atoms and molecules are always in motion. The energy associated with this motion is termed kinetic energy.

The amount of kinetic energy that a particle has is a direct function of temperature, and it is the kinetic energy of the water molecules under different conditions that determines the different properties of the three states of water as shown in Figure 2.5 . Atoms and molecules move in different ways under different conditions because of the forces attracting them to each other, called intermolecular forces. Intermolecular forces is a general term describing the fact that all atoms, and molecules share a certain inherent attraction for each other. These attractive forces are much weaker than the bonds that hold molecules together, but in a large cluster of atoms or molecules the sum of all of these attractive forces can be quite significant. Now, consider a group of molecules or atoms clustered together and held in place by these attractive forces. At low temperature, the molecules or atoms will remain stuck together in a lump of defined shape and structure, like water in the form of an ice cube. This is referred to as the solid phase. At the atomic level, the molecules or atoms in a solid are closely packed, and although they are still all rapidly moving, their movements are so small that they can be thought of as vibrating about a fixed position.

As an analogy here, think of a handful of small magnets stuck together in a solid mass (Figure 2.6) . Solids and liquids are the most tightly packed states of matter. Because of the intermolecular forces, solids have a defined shape, which is independent of the container in which they are placed. As energy is added to the system, usually in the form of heat, the individual molecules or atoms acquire enough energy to overcome some of the attractive intermolecular forces between them so that neighboring particles are free to move past or slide over one another. This state of matter is called the liquid phase. As in a solid, in a liquid, the attractive forces are strong enough to hold the molecules or atoms close together so they are not easily compressed and have a definite volume. Unlike in a solid, however, the particles will flow (slide over each other) so that they can assume the shape of their container, as shown in Figure 2.7 . Finally, if enough energy is put into the system, the individual molecules or atoms acquire enough energy to totally break all of the attractive forces between them and they are free to separate and rapidly move throughout the entire volume of their container.

This is called the gas phase and atoms or molecules in the gas phase will totally fill whatever container they occupy, taking on the shape and volume of their container. Because there is so much space between the particles in a gas, a gas is highly compressible, which means that the molecules can be forced closer together to fit in a much smaller space (Figure 2.8) . We are all familiar with cylinders of compressed gas, where the compressibility of gasses is exploited to allow a large amount of gas to be transported in a very small space. Figure 2.9 shows a simple graphic representation of the atomic states in solids, liquids and gasses. Returning to our example of water, at low temperature, water exists as the solid, ice. As the solid is warmed, the water molecules acquire enough energy to overcome the strongest of the attractive forces between them and the ice melts to form liquid water. This transition from the solid phase to the liquid phase happens at a fixed temperature for each substance called the melting point. The melting point of a solid is one of the physical properties of that solid. If we remove energy from the liquid molecules they will slow down enough for the attractive forces to take hold again and a solid will form.

The temperature that this happens is called the freezing point and is the same temperature as the melting point. As more energy is put into the system, the water heats up, the molecules begin moving faster and faster until there is finally enough energy in the system to totally overcome the attractive forces. When this happens, the water molecules are free to fly away from each other, fill whatever container they are occupying and become a gas. The transition from the liquid phase to the gas phase happens at a fixed temperature for each substance and is called the boiling point. Like the melting point, the boiling point is another physical property of a liquid. Phase transitions for a typical substance can be shown using simple diagram showing the physical states, separated by transitions for melting and boiling points. For example, if you are told that a pure substance is 15˚ C above its boiling point, you can use the diagram to plot the temperature relative to the boiling point. Because you are above the boiling point, the substance will exist in the gas phase. Example 2.1 The Physical State of a Substance There are, however, some exceptions to the rules for changes of state that we have just established,.

For example, ice is a solid and the molecules in the interior are held together tightly by intermolecular forces. Surface molecules, however, are exposed and they have the opportunity to absorb energy from the environment (think of a patch of snow on a bright sunny day). If some of these surface molecules absorb enough energy, they can break the attractive forces that are holding them and escape as a gas (water vapor) without ever going through the liquid phase. The transition from a solid directly into a gas is called sublimation. The reverse process, a direct transition from a gas to a solid, is called deposition. Perhaps the most common example of a solid that does not melt, but only sublimes, is dry ice (solid carbon dioxide;CO2), shown in Figure 2.10 . This property of dry ice is what makes it a good refrigerant for shipping perishables. It is quite cold, keeping things well frozen, but does not melt into a messy liquid as it warms during shipment. Just like surface molecules in solids can move directly into the gas phase, surface molecules in liquids also absorb energy from the environment and move into the gas phase, even though the liquid itself is below the boiling point.

This is the process of vaporization (evaporation). The reverse process, a transition from a gas to a liquid, is called condensation. Liquid substances undergo vaporization and the space above any liquid has molecules of that substance in the gas state. This is called the vapor pressure of the liquid, and vapor pressure (at a given temperature) is another of the physical properties of liquid substances. Summarizing what we know about the different states of matter: In a gas: the molecules or atoms are highly separated, making a gas highly compressible, attractive forces between the particles are minimal, allowing the gas to take on the shape and volume of its container. In a liquid: the molecules or atoms are closely spaced, making a liquid much less compressible than a gas, attractive forces between the particles are intermediate, allowing the molecules or atoms to move past, or slide over one another, liquids have a definite volume, but will take on the shape of their container. In a solid: the attractive forces are strong, keeping the atoms or molecules in relatively fixed positions, the neighboring atoms or molecules are close together, making the solid not compressible and giving it a definite shape that is independent of the shape and size of its container.

Exercise 2.2 States of Matter 2.3 Density, Proportionality and Dimensional Analysis[ edit ] In the previous section, we have learned about the states of matter. The physical state of a substance at under a defined set of conditions (like temperature and pressure) is an intensive property of a substance. An intensive property is defined as a property that is inherent to the substance and is not dependent on the sample size. Density, the mass-to-volume ratio of a substance, is another example of an intensive property. (Figure 2.11) If you picked up equal sized samples of aluminum and gold, you would immediately notice that one was much heavier than the other. The atomic mass of gold is over seven times greater than the atomic mass of aluminum, so although the two samples are the same size, the lump of gold is significantly more massive than the equally sized lump of aluminum. We can say that gold is more dense than aluminum. Making this a quantitative measurement, one cubic centimeter of gold has a mass of 19.3 grams (remember that a cubic centimeter is the volume of a cube that is exactly one cm on each side, and it has the units of cm3[ ;see Figure 2.12].

We defined density as the mass-to-volume ratio of a substance. For gold, the mass is 19.3 grams and the volume is 1 cm3. The mass-to-volume ratio of gold is ( ) {\displaystyle \left({}^{2.{\text{70 g}}}\!\!\diagup \!\!{}_{{\text{1 cm}}^{\text{3}}}\;\right)} , and the density of aluminum is therefore 2.70 g/cm3, about 7 times less than that of gold. Density is a physical property that can be measured for all substances, solids, liquids and gasses. For solids and liquids, density is often reported using the units of g/cm3. Densities of gasses, which are significantly lower than the densities of solids and liquids, are often given using units grams/liter (g/L, remembering from Section 1.4 that a liter is defined as 1000 cm3). Table 2.1 gives the densities of some common solids, liquids and gasses. The definition of density that we used previously was the mass-to-volume ratio of a substance. This is also stated as “mass per unit volume”.

The word per in this context implies that a mathematical relationship exists between mass and volume. In this case, the relationship is the ratio of mass-to-volume. Whenever two factors can be related by a ratio or fraction we can use unit analysis to solve problems relating those factors. For density, the ratio is mass-to-volume. If a sample of iron has a mass of 23.4 grams and a volume of 3.00 cm3, the density of iron can be calculated as: d = 3 ) {\displaystyle \left({}^{2{\text{3}}{\text{.4 g}}}\!\!\diagup \!\!{}_{{\text{3}}{\text{.00 cm}}^{\text{3}}}\;\right)} or, d = 7.80 g/cm3 In this calculation, our two experimental numbers are 23.4 and 3.00. Each of these numbers has three significant figures (remember, the trailing zeros in 3.00 are significant because the number has a decimal point). Our answer must therefore also be accurate to three significant figures, or 7.80.

Example 2.3 Calculating the Density of a Solid:Converting Length to find Volume. Example 2.4 Calculating Density of a Solid:Converting Mass and Volume. Example 2.5 Calculating the Density of a Solid:Converting Mass. 2.4 Chemical Properties, Physical Changes and Chemical Changes[ edit ] A lump of gold can be hammered into a very thin sheet of gold foil (it is the most malleable of all of the elements). Nonetheless, the gold in the foil sheet is still just elemental gold;nothing has changed except the physical appearance of the sample. The same is true if you take any solid pure substance and melt it, or convert it to a gas. The atomic or molecular structure of the substance has not changed, it simply has a different physical appearance. Changes in outward appearances that do not alter the chemical nature of the substance and make no new substance are called physical changes. Pure carbon, in the form of a briquette, can be smashed to a fine power without changing the fact that it is still just elemental carbon (thus, this is a physical change), but if pure carbon is heated in the presence of oxygen, something else happens.

The carbon slowly disappears (often in flames) and the carbon atoms now appear as a compound with oxygen with the formula CO2. Carbon dioxide is a totally different substance than either the carbon or the oxygen that we started with. For example, carbon is a black solid and carbon dioxide is a colorless gas. You know that a chemical change has occurred when the chemical composition of the material changes and a new substance is produced. (Figure 2.13) Just like we defined a set of physical properties for substances, we can also define a set of chemical properties. Chemical properties are simply the set of chemical changes that are possible for that substance. For the element magnesium (Mg), we could say that chemical properties include: the reaction with oxygen to form MgO, the reaction with hydrochloric acid to form MgCl2 and hydrogen gas (H2), the reaction with solid carbon dioxide (dry ice) to form MgO and carbon. Chemical changes can almost always be detected with one of our physical senses.

Thus, when magnesium reacts with oxygen (burns in air) a bright white flame is produced, heat is evolved and the shiny metallic magnesium is converted to a crumbly white powder (MgO; (Figure 2.14a) . In the reaction with hydrochloric acid (the molecule HCl dissolved in water), the solid metallic magnesium disappears, bubbles of hydrogen gas (H2) are evolved, heat is produced, and a clear solution containing MgCl2 is formed (Figure 2.14b) . In the reaction with solid carbon dioxide (dry ice), a bright white flame is produced, heat is evolved and the shiny metallic magnesium is converted to a crumbly white powder and solid carbon (Figure 2.14c) . In general, when you are trying to identify a chemical change, look for evidence of heat or light, the evolution of a gas, a change in color or the formation of new solid products from otherwise clear solutions. Exercise 2.4 Chemical and Physical Changes 2.5 Conservation of Mass and Chemical Changes[ edit ] When substances undergo chemical changes their physical state is usually dramatically altered. Despite this dramatic change, however, no matter is lost or created.

We can show this with the reaction of magnesium metal with oxygen to form magnesium oxide (Figure 2.14) . Instead of burning the magnesium metal openly in the air, if you were to seal the magnesium and air together in a glass vessel, weigh it, heat it to promote reaction, and then weigh the vessel again, you would find that there was no change in total mass. The mass of the product, magnesium oxide, would exactly equal the masses of the substances that reacted (oxygen gas and magnesium metal). This is analogous to an experiment performed by the French chemist, Lavoisier, in the 1770s in which he heated metallic tin (Sn) with air in a closed vessel. This, and other experiments of the time, provided the data that led to the law of mass conservation. Formally, the law states, there is no detectable change in the total mass of materials when they react chemically to form new materials. Basically, what the conservation law says is that whenever a chemical change occurs, the total mass of the substances reacting must equal the total mass of the substances that are produced. Sometimes this is stated as mass is conserved or mass is neither created nor destroyed in a chemical reaction.

For example, when charcoal is burned in oxygen, the mass of the (charcoal + oxygen) must equal the mass of the (carbon dioxide, water vapor and ash) that is produced. The conservation of mass is one of the fundamental principles on which modern chemistry is based. Study Points[ edit ] A compound is defined as a substance that results from the combination of two or more elements in a constant ratio. In a compound such as water, we show the ratio of the elements (hydrogen and oxygen) by using subscripts on the chemical symbols for each element. Thus, water (two hydrogens and one oxygen) is written using the chemical formula H2O. In a molecule, the atoms are not only bonded together in a constant ratio, but they are also bonded in a specific geometric arrangement. A pure substance contains only one kind of matter;it can be a single element or a single chemical compound. Two or more pure substances mixed together constitute a mixture;you can always separate a mixture by simple physical means. A heterogeneous mixture is not uniform and different samples of the mixture will have a different compositions. A homogeneous mixture, is uniform and any sample that you examine will have exactly the same composition as any other sample.

Within chemistry, the most common type of homogeneous mixture is a solution. Any pure substance, under appropriate conditions, can exist in three different states: solids, liquids and gases. States of matter are examples of physical properties of a substance. Other physical properties include appearance (shiny, dull, smooth, rough), odor, electrical conductivity, thermal conductivity, hardness and density, etc. Solids have both a definite shape and volume. Liquids have a definite volume, but take on the shape of their container. Gasses have neither a definite shape nor volume, and both of these are defined by the shape and volume of their container. The kinetic molecular theory (KMT) is generally used to explain physical states of matter. The KMT suggests that atoms and molecules are always in motion and are loosely bound to each other by attractive called intermolecular forces. In a solid, the kinetic energy (energy of motion) associated with the atoms or molecules is insufficient to break these forces and the particles are essentially fixed in place, adjacent to each other. In a liquid, there is enough kinetic energy to break some of the attractive forces, allowing the particles to “slip and slide” next to each other, but there is not enough energy to allow them to escape.

In a gas, there is sufficient kinetic energy to totally overcome the forces and the particles have no interactions with each other. A change of state from a solid to a liquid occurs at a defined temperature (which) called the melting point (or freezing point);this temperature is a unique physical property of the substance. The transition from a liquid to a gas, likewise, occurs at the boiling point. A direct transition from a solid to a gas is called sublimation. An intensive property is defined as a property that is inherent to the substance and is not dependent on the sample size. Density, the ratio of mass-to-volume for a substance, is a classic example of an intensive property. Density is calculated by taking the mass of a sample of a substance, and dividing that by the volume of that sample. Density for solids is typically expressed using units of grams per cubic centimeter (g cm-3);liquids as grams per milliliter (g mL-1) and gasses as grams per liter (g L-1), although any mixture of mass and volume units may be used. Remember, a mL has the same volume as a cm3, and a L is simply 1000 mL.

Physical changes are changes in outward appearances that do not alter the chemical nature of the substance and produce no new substance. When a chemical change occurs, a new substance is produced. Just like physical properties describe the appearance or intensive properties of a substance, chemical properties describe the set of chemical changes that are possible for that substance. The law of mass conservation (conservation of mass) simply states, that there is no detectable change in the total mass of materials when they react chemically (undergo a chemical change) to form new substances. Matter, Compound and Mixture | Chemistry tutorials Matter, Compound and Mixture General chemistry , Inorganic chemistry chemistry , compounds , hetergeneous cmpounds , homogeneous compounds , inorganic , matter , metalloids , metals , mixture , non metals , organic , pure and impure kc What is chemistry? Chemistry is the branch of science that deals with investigation of substance from which matter are composed. Our universe is made up of matter and energy. Matter: Matter is part and constitute of our nature which occupies space, can be felt and have definite mass. Water, air, soil, animals plants are all examples of matter. The amount of matter present in any object is called its mass.

On the basis of physical state, Matter can be classified as Solid Gas Chemical classification Chemical classification of substance is based upon its composition. By this method, a matter is classified as: Pure Pure substance Substance made up of only one kind of atoms or molecules are known as pure compounds. A pure substance always have definite composition. The simplest form of a pure substance is its element. Element is the simplest form of any matter. In Earth there are 90 naturally occurring elements starting from hydrogen to …. These elements are placed in periodic table based on their atomic properties. Rest of the elements known are created artificially by laboratory methods. All these elements have their own identity with specific properties. For example hydrogen, oxygen, carbon etc are elements. In earth, only 20 elements are abundantly found in the crust, Oxygen, Calcium, Iron, Aluminum are some. Other elements are found in lower proportion. In the environment, elements react with each other to form various compound. Compound When two or more elements combine in definite proportion, then a compound is formed. A compound is formed when elements react with each other chemically. When a compound is dissociated, it splits into constituent element. For example, Hydrogen and Oxygen combine to form water.

2H2 + O2 = 2H2O Here hydrogen and Oxygen are pure elements while H2O is compound. When H2O is dissociated chemically, it breaks down into hydrogen and oxygen. Compounds can be divided as Inorganic compounds: In general, compounds which are obtained from non living sources are called inorganic compounds. As many molecules have biological origin, specially from living cells, those molecules which don’t origin from living cells are traditionally considered as inorganic. for example, rock salt, Alkaline earth metal oxides, silicon, oxygen compounds, etc are all inorganic compounds. Organic compounds: Very basically, compounds which are obtained form living source are called organic compounds. biological molecules and compounds which have chief element as carbon and hydrogen are organic compounds. proteins, oils, fuels etc are organic compounds. Elements can be further classified into Metals, non-metals and Metalloids. Metals: In chemistry metals means those which have tendency to lose electron to form electro positive ions. Metals are usually solid (exception Mercury), reflect light and have luster. Metals are good conductors of heat and electricity.

They are malleable which is why metal are widely used to make metallic sheets and other appliances. Iron, Aluminum, Zinc, Silver, Gold, Tin are common examples of Metals. Non Metals: Non-metals are those elements which tends to gain electron to form electro negative ions. These elements are poor conductor of electricity and heat. Also, non-metals don’t have metallic properties like luster (except iodine) and they don’t reflect light. Common examples of non-metals are electro negative elements like halogens (F, Cl, Br, I), oxygen, Nitrogen, Phosphorus etc. Non-metals can be found in all three state i.e. Solid, Liquid and gas. Metalloids: Metalloids are those elements which shows intermediate behavior between metals and non-metals. Silicon, Boron, Arsenic, polonium, Antimony etc are example of metalloids. 2. Mixture (impure substance) A mixture is compound formed by mixing of two or more elements in any proportion. In the mixture the mixing components don’t lose its identity. For example air in atmosphere is a mixture of different gases like nitrogen, oxygen, carbon and others.

Mixture can be two kinds: a. Homogenous mixture: A homogenous mixture is such mixture where there is uniform composition of components throughout the sample. For example oil, kerosene, etc have uniform mixture of different hydrocarbons. Homogenous mixture are also called solution. If a small portion of homogenous mixture is taken, there will be uniform proportion of mixing component as like in the entire solution. b. Heterogeneous mixture: Mixture like sand and sugar is example of heterogeneous mixture. In such mixture there is no uniform mixing of components and hence cannot be represented by formula. Heterogeneous mixture can have different phase like gas and liquid, solid and liquid etc. Difference between Mixture and Compound. Mixture Nature & Classification of Matter< chemistry< high school< ICSE CBSE< mentorials.com Created: 19 Jan, 2010; Last Modified: 14 Oct, 2016 Matter - 01 Nature of Matter Anything that we see around us is made up of matter. Matter is anything which has mass and occupies space. Properties A property is any characteristic of matter which can be detected or measured, and can be used to identify or describe the matter.

Properties can be of two types – physical properties and chemical properties. A substance is matter which can be identified by a fixed set of properties. A physical property of matter can be determined without carrying out any chemical reaction on it. Thus, for example, properties like colour of gold or the boiling point of water are physical properties. A chemical property of matter is determined only when the matter reacts with another kind of matter and converts to a third kind. Thus, a new shiny iron nail reacts with oxygen in air over time to form a layer of brown rust covering the nail. This reaction of iron with oxygen is one of its chemical properties. Properties can also be classified as being qualitative or quantitative. Qualitative properties are those which can only be described and cannot be measured and expressed numerically, such as the colour of gold. Quantitative properties can be measured and expressed numerically, such as the boiling point of water, which is 100° C . Yet another classification of properties is into extensive properties and intensive properties. Extensive properties depend on the amount of matter present, such as the mass or the volume of a sample. Intensive properties do not depend upon the amount of matter, such as density and freezing point. Incidentally, all chemical properties are intensive properties.

Each substance has its own unique set of properties which differentiate it from other substances. Particles All matter is made up of very small particles, so small that they cannot be seen with the naked eye. These particles are separated from each other by emptiness. A lot of the properties of matter becomes clear by understanding how these particles behave. Today we refer to these particles as atoms and molecules. Atoms are the smallest particles of interest to chemistry, while molecules are collection of atoms which behave as a single unit. For some kinds of matter, atoms are the smallest units, while for others, molecules are. Classification of Matter Two major categories of classification of matter are physical classification and chemical classification. Fig. depicts the classification of matter into the two major categories, and the sub-classifications therein. Fig 1: Classification of Matter Physical Classification This classification divides matter into three categories – solids, liquids, and gases – known as the three states (or phases) of matter. (Fig. ) States of Matter Solid Fig 2: A conceptual view of particles of crystalline common salt (sodium chloride). The lines between the particles are drawn to illustrate the structure—they do not exist in reality. Solids are matter having fixed shape, fixed volume and are almost impossible to compress.

Of course, solids can be crushed into powder form (in which case the fixed shape is destroyed), but in essence the powder still remains a solid. Solids are composed of particles which are very near to each other because of mutual forces of attraction, and thus in some kind of order. The particles' movement is limited to vibrating in the positions they are in. If energy is added to the solid in the form of heat, the particles become more energetic in their vibrations. Amorphous solids have no such small units and hence their internal structure is shapeless. Common salt (sodium chloride) is crystalline with cubic crystals (Fig. ). Glass, on the other hand, is an amorphous solid as it has no such internal structure with definite shape. Liquid Liquids are matter having a fixed volume but no fixed shape – they take the shape of the container. Liquids are very difficult to compress. Liquids are composed of higher energy particles which overcome their mutual forces of attraction and move independently. This is the reason why liquids do not have a fixed shape. The particles move in straight lines until they collide with other particles and rebound. Since the particles are a little more spread apart when compared to solids, liquids can be compressed a little.

For a liquid in a container, its top free surface consists of moving particles which are attracted by the particles below, and do not have energy enough to overcome the attraction. As a result, they remain within the boundary of the top surface and cannot escape, giving the liquid the fixed volume. Gas Gases are matter having neither a fixed shape nor a fixed volume. They are very easy to compress. Gases consist of high energy particles which are so far from each other that the forces of attraction between them become negligible. The particles can spread out to occupy whatever space is available. Thus, gases have neither fixed shape nor fixed volume. Change of State Fig 3: Change of State Matter can undergo changes between these three physical states through changes in physical properties, but without involving any change in chemical properties. Such changes are called physical changes. Energy is either absorbed or released during a physical change. The change of state from solid to liquid is called melting or fusion, while the reverse process is called freezing or solidification. The melting point is the temperature at which a substance changes from solid to liquid. Conversely, freezing point is the temperature at which a substance changes from a liquid to solid.

These two temperatures are essentially the same – which one is used depends upon whether the substance is being heated or being cooled. The change of state from liquid to gas is called vaporisation or boiling, while the reverse process is called condensation. The boiling point is the temperature at which a substance changes from liquid to gas. Conversely, condensing point is the temperature at which a substance changes from a gas to liquid. When liquids gradually turn into gases at temperatures less than their boiling point, the process is called evaporation. Some substances, like iodine and solid carbon dioxide, can go directly from solid to gaseous state without melting – this is known as sublimation. The reverse process of sublimation is called deposition. Chemical Classification A chemical change involves a chemical reaction resulting in change in chemical properties of the substance. In any chemical change, (1) one or more substances are used up (at least partially), (2) one or more new substances are formed, and (3) energy is absorbed or released. The chemical properties of substances are revealed as they undergo chemical changes. The chemical classification scheme broadly divides matter into two categories – pure substances and mixtures.

Pure Substances A pure substance (or simply substance) is matter which can be identified by a fixed set of properties, which distinguishes it from other substances. A substance cannot be further broken down into simpler substances by physical means (i.e. through physical changes), although some substances can be broken down through chemical means (through chemical changes). A sample of pure water has a fixed freezing point of 273 K (0° C ), a boiling point of 373 K (100° C ) and a density of 1000 kg / m 3, irrespective of where the sample is derived from. Such properties identify water as a unique substance, with no other substance matching these characteristics. Elements sodium (natrium) Na An element is a pure substance which cannot be further split up by chemical reactions into simpler substances. They are the fundamental substances of which all matter is composed. The smallest particle of an element of importance to chemistry is the atom. There are 115 known elements presently, out of which only 91 occur naturally. The remaining elements have been produced artificially by nuclear scientists in the laboratory using particle accelerators. To simplify the representation of elements in chemical reactions, they are represented by symbols.

Basically, the symbol of an element refers to one atom of the element. Some symbols are derived from the latin name of the particular elements. The names and symbols of some common elements are listed in Table . Elements may be solids, liquids or gases. At room temperatures, only mercury, bromine and francium are liquids. Hydrogen, nitrogen, oxygen, fluorine, chlorine and the noble gases (helium, neon, argon, xenon, krypton and radon) are gases. The rest of the elements are solids. The Periodic Table is a chart of elements presenting details about all of them. Elements are further classified as metals, non-metals & metalloids. About 80% of elements are metals. Metals are elements which have “metallic” lustres, are malleableA malleable substance can be hammered into thin sheets. and ductileA ductile substance can be drawn out as thin wires. , are of high relative density, and are good conductors of heat and electricity. All metals are solid except mercury, which is the only liquid metal at room temperature. Non-metals do not possess any of the properties of metals.

They do not have a lustre, are not malleable or ductile, and do not have high relative density. Non-metals are solids or gases except bromine, which is the only non-metal which is liquid at room temperature. Metalloids (or semi-metals) are those elements which exhibit both the properties of metals and non-metals to some extent, such as boron and silicon. Compounds A compound is a pure substance which is formed by chemical combination of two or more elements in a fixed ratio by mass. Compounds are the substances which can be decomposed by chemical methods into their constituent elements. The smallest unit of a compound, known as a molecule, or a formula unit, is composed of atoms of the constituent elements. A compound is represented by a chemical formula which indicates one molecule (formula unit) of the compound containing atoms of its elements. The number of possible compounds is almost infinite. A chemical compound always contains the same elements chemically combined together in a fixed proportion by weight. A compound has properties which are very much different from its constituent elements. Those compounds which are composed of carbon and hydrogen, along with other elements, are called organic compounds, as these compounds form the basis of all life on earth.

All other compounds are categorised under the name of inorganic compounds. (a) Water, chemically known as hydrogen monoxide, is a compound which contains hydrogen and oxygen combined in the ratio of 1:8 by weight. Its chemical formula is H2O. It is a liquid which cannot catch fire, though it is made up of hydrogen, a gas which is combustible, and oxygen, another gas which supports combustion. Thus, the properties of water are very much different from its constituent elements. Water can be decomposed into hydrogen and oxygen by the passage of electric current through it. (b) Common salt, or sodium chloride, is a compound of sodium, a soft silvery highly reactive metal, and chlorine, a greenish poisonous gas. But common salt is non-poisonous and essential part of our diet. Mixtures A mixture is a sample of matter containing two or more pure substances physically mixed together, without any chemical interaction, in any ratio by weight. Since the mixture is formed by physical combination of substances, the substances making up the mixture do not lose their individual properties. Also, as the components of the mixture can be present in any ratio by weight, it is possible to have mixtures in varying concentrations.

Mixtures are categorised into homogeneous and heterogeneous mixtures. A homogeneous mixture (or a uniform mixture) is one in which the composition is the same throughout. A homogeneous mixture is also called a solution, and consists of a substance designated as a solventA solvent is a substance, usually a liquid, having the power of dissolving other substances in it. (the substance present in largest amount) and other substances (one or more) as solutesA solute is a substance that is dissolved in a solvent to form a solution. . Generally, a solvent is a liquid, while solutes can be solid, liquid or gaseous. A solution with water as the solvent is termed an aqueous solution. An alloy is a solution of two or more metals, and generally stands for a solid solution of the metals. An alloy of mercury with a metal is called an amalgam. Liquids that mix together completely are called miscible liquids. The final solution looks like a single liquid. In contrast, liquids which do not mix completely and tend to settle down as different layers are said to be immiscible.

Soda water is an example of a homogeneous mixture or solution, in which water (a liquid) is the solvent and carbon dioxide (a gas) is the solute. Brass is another example (a solid solution) in which copper is the solvent and zinc the solute. A heterogeneous mixture (or a non-uniform mixture) is one in which the composition varies throughout. A rock can be classified as a heterogeneous mixture. It generally consists of a number of mineral components distributed non-uniformly. In any mixture, (a) the composition can be varied and (b) each component of the mixture retains its own properties. Mixtures can be separated into component substances by physical means because each component retains its properties. Table 2: Examples of different types of mixtures. Type of Mixture

Question: In chemistry, a 'homogeneous mixture composed of only one phase' (basically a mixed yet uniform substance) is called a?
Answer: Solution