Query: We simply could never release enough CO2 into the atmosphere to cause the pH to go below 7 [the point in the pH scale at which a solution becomes acidic].”

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PH <=SEP=> In chemistry , pH ( -LSB- piːˈeɪtʃ -RSB- ) ( potential of hydrogen ) is a numeric scale used to specify the acidity or basicity of an aqueous solution . It is approximately the negative of the base 10 logarithm of the molar concentration , measured in units of moles per liter , of hydrogen ions . More precisely it is the negative of the logarithm to base 10 of the activity of the hydrogen ion . Solutions with a pH less than 7 are acidic and solutions with a pH greater than 7 are basic . Pure water is neutral , at pH 7 , being neither an acid nor a base . Contrary to popular belief , the pH value can be less than 0 or greater than 14 for very strong acids and bases respectively .   pH measurements are important in agronomy , medicine , biology , chemistry , agriculture , forestry , food science , environmental science , oceanography , civil engineering , chemical engineering , nutrition , water treatment and water purification , as well as many other applications .   The pH scale is traceable to a set of standard solutions whose pH is established by international agreement .  Primary pH standard values are determined using a concentration cell with transference , by measuring the potential difference between a hydrogen electrode and a standard electrode such as the silver chloride electrode .  The pH of aqueous solutions can be measured with a glass electrode and a pH meter , or an indicator .

Carbon dioxide <=SEP=> Carbon dioxide ( chemical formula ) is a colorless gas with a density about 60 % higher than that of air ( 1.225 g/L ) that is odorless at normally encountered concentrations . Carbon dioxide consists of a carbon atom covalently double bonded to two oxygen atoms . It occurs naturally in Earth 's atmosphere as a trace gas at a concentration of about 0.04 percent ( 400 ppm ) by volume . Natural sources include volcanoes , hot springs and geysers , and it is freed from carbonate rocks by dissolution in water and acids . Because carbon dioxide is soluble in water , it occurs naturally in groundwater , rivers and lakes , ice caps , glaciers and seawater . It is present in deposits of petroleum and natural gas .   As the source of available carbon in the carbon cycle , atmospheric carbon dioxide is the primary carbon source for life on Earth and its concentration in Earth 's pre-industrial atmosphere since late in the Precambrian has been regulated by photosynthetic organisms and geological phenomena . Plants , algae and cyanobacteria use light energy to photosynthesize carbohydrate from carbon dioxide and water , with oxygen produced as a waste product .   Carbon dioxide is produced by all aerobic organisms when they metabolize carbohydrates and lipids to produce energy by respiration . It is returned to water via the gills of fish and to the air via the lungs of air-breathing land animals , including humans . Carbon dioxide is produced during the processes of decay of organic materials and the fermentation of sugars in bread , beer and winemaking . It is produced by combustion of wood and other organic materials and fossil fuels such as coal , peat , petroleum and natural gas .   It is a versatile industrial material , used , for example , as an inert gas in welding and fire extinguishers , as a pressurizing gas in air guns and oil recovery , as a chemical feedstock and in liquid form as a solvent in decaffeination of coffee and supercritical drying . It is added to drinking water and carbonated beverages including beer and sparkling wine to add effervescence . The frozen solid form of , known as `` dry ice '' is used as a refrigerant and as an abrasive in dry-ice blasting .   Carbon dioxide is the most significant long-lived greenhouse gas in Earth 's atmosphere . Since the Industrial Revolution anthropogenic emissions - primarily from use of fossil fuels and deforestation - have rapidly increased its concentration in the atmosphere , leading to global warming . Carbon dioxide also causes ocean acidification because it dissolves in water to form carbonic acid .

Acid <=SEP=> An acid is a molecule or ion capable of donating a hydron ( proton or hydrogen ion H + ) , or , alternatively , capable of forming a covalent bond with an electron pair ( a Lewis acid ) .   The first category of acids is the proton donors or Brønsted acids . In the special case of aqueous solutions , proton donors form the hydronium ion H3O + and are known as Arrhenius acids . Brønsted and Lowry generalized the Arrhenius theory to include non-aqueous solvents . A Brønsted or Arrhenius acid usually contains a hydrogen atom bonded to a chemical structure that is still energetically favorable after loss of H + .   Aqueous Arrhenius acids have characteristic properties which provide a practical description of an acid . Acids form aqueous solutions with a sour taste , can turn blue litmus red , and react with bases and certain metals ( like calcium ) to form salts . The word acid is derived from the Latin acidus/ac ēre meaning sour . An aqueous solution of an acid has a pH less than 7 and is colloquially also referred to as ` acid ' ( as in ` dissolved in acid ' ) , while the strict definition refers only to the solute . A lower pH means a higher acidity , and thus a higher concentration of positive hydrogen ions in the solution . Chemicals or substances having the property of an acid are said to be acidic .   Common aqueous acids include hydrochloric acid ( a solution of hydrogen chloride which is found in gastric acid in the stomach and activates digestive enzymes ) , acetic acid ( vinegar is a dilute aqueous solution of this liquid ) , sulfuric acid ( used in car batteries ) , and citric acid ( found in citrus fruits ) . As these examples show , acids ( in the colloquial sense ) can be solutions or pure substances , and can be derived from acids ( in the strict sense ) that are solids , liquids , or gases . Strong acids and some concentrated weak acids are corrosive , but there are exceptions such as carboranes and boric acid .   The second category of acids are Lewis acids , which form a covalent bond with an electron pair . An example is boron trifluoride ( BF3 ) , whose boron atom has a vacant orbital which can form a covalent bond by sharing a lone pair of electrons on an atom in a base , for example the nitrogen atom in ammonia ( NH3 ) . Lewis considered this as a generalization of the Brønsted definition , so that an acid is a chemical species that accepts electron pairs either directly or by releasing protons ( H + ) into the solution , which then accept electron pairs . However , hydrogen chloride , acetic acid , and most other Brønsted-Lowry acids can not form a covalent bond with an electron pair and are therefore not Lewis acids . Conversely , many Lewis acids are not Arrhenius or Brønsted-Lowry acids . In modern terminology , an acid is implicitly a Brønsted acid and not a Lewis acid , since chemists almost always refer to a Lewis acid explicitly as a Lewis acid .