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9 August, 21:45

Calculate the pH of a buffer solution obtained by dissolving 13.0 g of KH 2 PO 4 (s) and 32.0 g of Na 2 HPO 4 (s) in water and then diluting to 1.00 L

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  1. 9 August, 21:52
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    7.58

    Explanation:

    Given that

    A buffer solution obtained by dissolving 13.0 g of KH₂PO₄ and 26.0 g of Na₂HPO₄ in water and then diluting to 1.00 L.

    pKa = 7.21.

    To get the PH we are going to use Henderson - Hasselblach equation:

    PH = Pka + ㏒ [A/AH]

    when the molar mass of Na2HPO4 = 142 g/mol

    and A is the conjugate base HPO4- - ions so,

    ∴[A] = 32g / 142 g/mol

    = 0.225 M

    and when the molar mass of KH2PO4 = 136 g/mol

    and AH is the weak acid H2PO4 - ions so,

    ∴[AH] = 13 g / 136 g/mol

    = 0.096 M

    and when we have the Pka value of H3PO4 = 7.21

    so, by substitution:

    ∴ PH = 7.21 + ㏒ (0.225 / 0.096)

    = 7.58
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