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19 December, 14:03

Determine the ph of a 0.18 m h2co3 solution. carbonic acid is a diprotic acid whose ka1 = 4.3 * 10-7 and ka2 = 5.6 * 10-11. determine the ph of a 0.18 m h2co3 solution. carbonic acid is a diprotic acid whose ka1 = 4.3 * 10-7 and ka2 = 5.6 * 10-11. 4.31 5.50 11.00 10.44 3.56

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  1. 19 December, 14:25
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    Answer is: ph value is 3.56.

    Chemical reaction 1: H₂CO₃ (aq) ⇄ HCO₃⁻ (aq) + H⁺ (aq); Ka₁ = 4,3·10⁻⁷.

    Chemical reaction 2: HCO₃⁻ (aq) ⇄ CO₃²⁻ (aq) + H⁺ (aq); Ka₂ = 5,6·10⁻¹¹.

    c (H₂CO₃) = 0,18 M.

    [HCO₃⁻] = [H⁺ ] = x.

    [H₂CO₃] = 0,18 M - x.

    Ka₁ = [HCO₃⁻] · [H⁺] / [H₂CO₃].

    4,3·10⁻⁷ = x² / (0,18 M - x).

    Solve quadratic equation: x = [H⁺] = 0,000293 M.

    pH = - log[H⁺] = - log (0,000293 M).

    pH = 3,56; second Ka do not contributes pH value a lot.
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