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1 June, 08:55

The leaves of the rhubarb plant contain high concentrations of diprotic oxalic acid (hooccooh) and must be removed before the stems are used to make rhubarb pie. if pka1 = 1.23 and pka2 = 4.19, what is the ph of a 0.0269 m solution of oxalic acid?

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  1. 1 June, 10:54
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    Chemical reaction (dissociation) 1: C₂O₄H₂ (aq) ⇄ C₂O₄H⁻ (aq) + H⁺ (aq).

    Chemical reaction (dissociation) 2: C₂O₄H⁻ (aq) ⇄ C₂O₄²⁻ (aq) + H⁺ (aq).

    c (C₂O₄H⁻) = c (H⁺) = x.

    c (C₂O₄H₂) = 0.0269 M.

    pKa₁ = 1.23.

    Ka₁ = 10∧ (-1.23) = 0.059.

    Ka₁ = c (C₂O₄H⁻) · c (H⁺) / c (C₂O₄H₂).

    0.059 = x² / (0.0269 M - x).

    Solve quadratic eqaution: x = c (H⁺) = 0.02 M.

    pH = - log (0.02 M) = 1.7.
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