The pKa for the first reaction is 5.85 and the pKa for the second reaction is 9.

Question

The pKa for the first reaction is 5.85 and the pKa for the second reaction is 9.00. Based on your two chemical equations, the increased concentration in carbon dioxide shifts the equilibria to the right. A. If the average pH of the Atlantic ocean surrounding the Bahamas dropped from 8.12 to 8.07 in 25 years, starting from 1989. By how much did the average acidity of the ocean increase? Express your answer as a percentage of 1989 acidity. B. Ocean pH may drop by another 0.30 unit by the end of this century. Assuming that the current concentration of ocean's ions (e.g. [Ca^+2] = 0.0106 M and [HCO^-_3] + [CO^2-_3] = 0.00211 M) remain the same, will the skeletal structures of marine organisms that are composed of CaCO_3 be soluble or insoluble in seawater in 2100? The Ksp value for aragonite (crystalline form of CaCO_3, which is found in coral and seashells) is 6.46 times 10^-7.

Explanation / Answer

(A)

Acidity means H+ concentration

pH=8.12

pH=-log[H+]

[H+]=10-pH=10-8.12=7.586*10-9

pH=8.07

[H+]=10-8.07=8.511*10-9

So increase in acidity=(8.511*10-9-7.586*10-9)/7.586*10-9=0.122=12.2%

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