Question

Determine the pH of each of the following solutions.


(a) 0.740 M carbonic acid (weak acid with K_a = 4.3e-07).

______________.

(b) 0.882 M hydrosulfuric acid (weak acid with K_a = 9.5e-08).

______________.

(c) 0.373 M pyridine (weak base with K_b = 1.7e-09).
______________.

Answer 1

A.

[H⁺]² = K_ac = 4.3e-07 * 0.740 = 3.82e-07 (WEAK ACID FORMULA)

[H⁺] = 5.640 * 10^-4 M

pH = 3.2486

B.

[H⁺]² = K_ac = 9.5e-08 * 0.882 = 8.379e-08 (WEAK ACID FORMULA)

[H⁺] = 2.894 * 10^-4 M

pH = 3.5384

C.

C5H5N + H2O (l) <---> OH- + C5H6N+
0.373____----------- _____0________0
-x ______ ----------- ______x________x
0.373-x __----------_______x _______ x

kb=1.7 x 10-9 = x2/ (0.373-x)

x² = 6.341 * 10^-10
x=2.5181
pOH= -log₁₀2.5181 * 10^-5 = 4.59892

14 - pOH= pH
14 - 4.59892 = pH = 9.40108