Determine the pH of the following aqueous solution.Initial concentrations are given.
[NaCHO₂] = 0.815 M,[HBr] = 0.105 M,K_a for HCHO₂= 1.8 × 10^-4

Question

Determine the pH of the following aqueous solution.Initial concentrations are given. [NaCHO₂] = 0.815 M,[HBr] = 0.105 M,K_a for HCHO₂= 1.8 × 10^-4 A)2.91 B)4.63 C)4.57 D)9.43 E)11.09

Quizplus · Accepted Answer

First, we need to write the equation for the dissociation of HCHO:
HCHO + H2O ⇌ H3O+ + CHO-
We can set up an ICE table:
I         0.815 M           0.105 M                0
C       -x                -x                     x
E      0.815-x         0.105-x              x
K = [H3O+][CHO-]/[HCHO]
Since x is << 0.815, we can approximate the equilibrium concentrations as:
[H3O+] ≈ x M
[CHO-] ≈ x M
[HCHO] ≈ 0.815 M
K = 1.8 × 10-4 = (x)(x)/(0.815-x)
Solving for x, we get x = 4.07 × 10-3 M
pH = -log[H3O+] = -log(4.07 × 10-3) = 4.57
Therefore, the answer is choice C.

Determine the PH of the Following Aqueous Solution