17.2 – 17.3 Student Notes

B. Polyprotic Acids

1. Def –

2. Write the two equilibrium reactions for sulfuric acid.

3. In general, the second ionization constant, K_a2, of a polyprotic acid is much _______ than the first ionization constant, K_a1. In the case of a triprotic acid, the third ionization constant K_a3, is much _____ than the second one, K_a2.

4. Calculating Concentrations of Species in a Solution of a Diprotic acid

Ascorbic acid (vitamin C) is a diprotic acid, H₂C₆H₆O₆. What is the pH of a 0.10 M solution? What is the concentration of ascorbate ion, C₆H₆O₆^2-? The acid ionization constants are K_a1 = 7.9 x 10^-5 and K_a2 = 1.6 x 10^-12.

5. The concentration of the ion A^2- ______ the second ionization constant, K_a2.

C. Base-Ionization Equilibria

1. Treated similarly to weak acids

2. Base ionization constant – K_b –

3. Write the base ionization constant for the following generic equation.

B (aq) + H₂O (l) ¯ HB⁺ (aq) + OH^- (aq)

4. Common places to find weak bases:

5. Calculating Concentrations of Species in a Weak Base Solution Using K_b

Morphine, C₁₇H₁₉NO₃, is administered medically to relieve pain. It is a naturally occurring base, or alkaloid. What is the pH of a 0.0075 M solution of morphine at 25° C? The base-ionization constant, K_b, is 1.6 x 10^-6 at 25° C.