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A Bjerrum plot is a graph of the concentrations of the different species of a polyprotic acid in a solution, as functions of the solution's pH, when the solution is at equilibrium. Due to the many orders of magnitude spanned by the concentrations, they are commonly plotted on a logarithmic scale. Sometimes the ratios of the concentrations are plotted rather than the actual concentrations. Occasionally H+ and OH− are also plotted. Most often, the carbonate system is plotted, where the polyprotic acid is carbonic acid (a diprotic acid), and the different species are carbonic acid, carbon dioxide, bicarbonate, and carbonate. In acidic conditions, the dominant form is ; in basic (alkalinic) conditions, the dominant form is CO32−; and in between, the dominant form is HCO3−. At every pH, the concentration of carbonic acid is assumed to be negligible compared to the concentration of CO2, and so is often omitted from Bjerrum plots. These plots are typically used in ocean chemistry to track the response of an ocean to changes in both pH and of inputs in carbonate and . The Bjerrum plots for other polyprotic acids, including silicic, boric, sulphuric and phosphoric acids, can also be constructed.〔 ==Bjerrum plot equations for carbonate system== If carbon dioxide, carbonic acid, hydrogen ions, bicarbonate and carbonate are all dissolved in water, and at chemical equilibrium, their equilibrium concentrations are often assumed to be given by: : : : where the subscript 'eq' denotes that these are equilibrium concentrations, ''K1'' is the equilibrium constant for the reaction + H+ + HCO3− (i.e. the first acid dissociation constant for carbonic acid), ''K2'' is the equilibrium constant for the reaction HCO3− H+ + CO32− (i.e. the second acid dissociation constant for carbonic acid), and DIC is the (unchanging) total concentration of dissolved inorganic carbon in the system, i.e. . ''K1'', ''K2'' and DIC each have units of a concentration, e.g. mol/litre. A Bjerrum plot is obtained by using these three equations to plot these three species against pH = –, for given ''K1'', ''K2'' and DIC. The fractions in these equations give the three species' relative proportions, and so if DIC is unknown, or the actual concentrations are unimportant, these proportions may be plotted instead. These three equations show that the curves for and HCO3− intersect at ()eq = ''K1'', and the curves for HCO3− and CO32− intersect at ()eq = ''K2''. Therefore, the values of ''K1'' and ''K2'' that were used to create a given Bjerrum plot can easily be found from that plot, by reading off the concentrations at these points of intersection. An example with linear Y axis is shown in the accompanying graph. It should be noted that the values of K1 and K2, and therefore the curves in the Bjerrum plot, vary substantially with temperature and salinity.〔Mook W (2000) Chemistry of carbonic acid in water. In 'Environmental Isotopes in the Hydrological Cycle: Principles and Applications' pp. 143-165. (INEA / UNESCO: Paris). () Retrieved 30NOV2013.〕 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Bjerrum plot」の詳細全文を読む スポンサード リンク
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