E N U 11. You have probably heard concerns about the acidification of earth\'s o
ID: 1028169 • Letter: E
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E N U 11. You have probably heard concerns about the acidification of earth's oceans as a result of the increase in atmospheric carbon dioxide. As the partial pressure of co2 in the atmosphere increases, so does its solubility in water. Dissolved co2 reacts with water to form carbonic acid, H2CO3-. Carbonic acid is a weak diprotic acid 80 Since the measurements began in the 18th century, the PH of ocean water has decreased from 8.2 to the present value of 8.07 A. Is most of the dissolved carbon dioxide in the form of CO2(aq)or H2CO3(aq)? B. Is the most of the H2CO3(aq) in the form of H2CO3(aq)or HCO3(aq)? C. By what percentage has the[H+]concentration changed over this time period?Explanation / Answer
(A) Formation constant of carbonic acid is very high. So, the dissolved carbon dioxide in ocean water is in the form of H2CO3 (aq).
(B) H2CO3 is a very weak diprotc acid and its first dissociation constant (that produces HCO3- from H2CO3) is very low. It indicates that a very less amount of H2CO3 dissociates. So, th epredominat form of carbonic acid is H2CO3 (aq).
(C) pH = -log[H+ ]
initial pH = 8.2, Initial concentration of H+ = 10-8.2 (M) = 6.31 *10-9 (M)
Final pH = 8.07, Final concentration of H+ = 10-8.07 (M) = 8.51 *10-9 (M)
Percentage change of H+ ion concentration:
(8.51 *10-9 - 6.31 *10-9) * 100/ 6.31 *10-9 % = 34.87%
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