Question

Equal volumes of three acid solutions of pH 3, 4 and 5 are mixed in a vessel. What will be the H⁺ ion concentration in the mixture?

• A. 3.7 × 10^–3 M
• B. 1.11 × 10^–3 M
• C. 1.11 × 10^–4 M
• D. 3.7 × 10^–4 M

Answer 1

Answer: (D)

3.7 × 10^–4 M

Answer 2

[H⁺] = 10^–3 M, [H⁺] = 10^–4 M, [H⁺] = 10^–5 M for the given acids.

M_mix V_mix = M₁V₁ + M₂V₂ + M₃V₃

M_mix × 3 = 10^–3 × 1 + 10^–4 × 1 + 10^–5 × 1

M_mix = $\frac{10^{- 5}\lbrack 100 + 10 + 1\rbrack}{3} = \frac{111 \times 10^{- 5}}{3}$ = 37 × 10^–5 M

= 3.7 × 10^–4 M