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30 December, 08:38

Calculate the pH of a 0.020 M H2CO3 solution. At 25 °C, Ka1 = 4.3 * 10-7. H2CO3 (aq) + H2O (l) ↔ H3O + (aq) + HCO3 - (aq)

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  1. 30 December, 08:59
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    H₂CO₃ (aq) + H₂O (l) ↔ H₃O⁺ (aq) + HCO₃⁻ (aq)

    Let d be the degree of dissociation

    .02 (1-d).02d. 02d

    Dissociation constant Ka₁ is given

    4.3 x 10⁻⁷ =.02d x. 02d /.02 (1-d)

    =.004 d² /.02 (neglecting d in denominator)

    =.02 d²

    d² = 215 x 10⁻⁷

    d = 4.636 x 10⁻³

    =.004636

    concentration of H₃O⁺

    = d x. 02

    =.004636 x. 02

    = 9.272 x 10⁻⁵

    pH = - log [ H₃O⁺ ]

    = - log (9.272 x 10⁻⁵)

    5 - log 9.272

    = 5 -.967

    = 4.033.
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