Textbook Question
Calculate the [H3O+] and pH of each polyprotic acid solution.
a. 0.125 M H2CO3
17. Acid and Base Equilibrium
Diprotic Acids and Bases Calculations
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Which of the following diprotic acid would produce the most acidic solution when dissolved?
A
0.200 M H2SO3 (Ka1 = 1.6 x 10-2 ; Ka2 = 4.6 x 10-5)
B
0.200 M H3PO4 (Ka1 = 7.5 x 10-3 ; Ka2 = 6.2 x 10-8 ; Ka3 = 4.2 x 10-13)
C
0.200 M H2CO3 (Ka1 = 4.3 x 10-7 ; Ka2 = 5.6 x 10-11)
D
0.200 M H2S (Ka1 = 8.9 x 10-8 ; Ka2 = 1.0 x 10-19)
E
0.200 M HC9H7O4 (Ka1 = 3.3 x 10-4)
Verified step by step guidance1
Identify that the problem involves comparing the acidity of different diprotic acids based on their dissociation constants (Ka values).
Understand that the acidity of a solution is determined by the concentration of hydrogen ions (H+) it produces. A higher Ka value indicates a stronger acid, which dissociates more completely to release more H+ ions.
For each acid, consider the first dissociation constant (Ka1) as it generally contributes the most to the acidity of the solution. Compare the Ka1 values of each acid: H2SO3, H3PO4, H2CO3, H2S, and HC9H7O4.
Recognize that H2SO3 has the highest Ka1 value (1.6 x 10^-2), indicating it is the strongest acid among the given options and will produce the most acidic solution.
Note that while H3PO4 has three dissociation constants, its first Ka value is lower than that of H2SO3, making H2SO3 the more acidic choice overall.
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