Question

What is (H+) in mol/L of a solution that is 0.20 M
CH3COONa and 0.10 M in CH3COOH ? (K, for
CH3COOH = 1.8×10^-5)
(1) 3.5 × 10^-4 (2) 1.1 x 10^-5
3) 1.8 x 10^-5 (4) 9.0 x 10^-6​

Answer 1

Answer ⇒ Option (d).

Explanation ⇒

CH₃COONa ------- CH₃COO⁻ + Na⁺

CH₃COONa is an strong salt which disassociates completely, thus,  CH₃COO⁻ = 0.2 M, Na⁺ = 0.20 M

CH₃COOH -------- CH₃COO⁻ + H⁺

c(1- α)                    cα                cα

Thus,

K = [CH₃COO⁻][H⁺]/[CH₃COOH]

K = (0.2 + cα)[H⁺]/[0.1 - cα]

1.8 × 10⁻⁵ = (0.2)[H⁺]/[0.1]   [Since, 0.1 - cα ≈ 0.1,  0.2 + cα = 0.2 ]

∴ 1.8 × 10⁻⁵ = 2[H⁺]

∴ [H⁺] = 0.9 × 10⁻⁵

∴ [H⁺] = 9 × 10⁻⁶

Hence, Option (d). is the correct choice.

Hope it helps.

Answer 2

option d is the correct answer

Explanation: log2=0.30