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7 November, 05:52

A buffer solution has 0.625 M HCN and 0.575 M CN-. If 0.030 moles of NaOH is added to 400. mL of the buffer solution, what is the pH after the addition? The pKa of hydrocyanic acid is 9.31.

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  1. 7 November, 08:32
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    pH = 9.393

    Explanation:

    Give that 400mL buffer 1L = 1000mL 0.625 mol of HCN solution = 0.250 mol HCN

    Therefore,

    400mL buffer solution 1L = 1000mL 0.575 mol CN^ - solution = 0.230 mol of CN^-

    Pka HCN = 9.31

    Therefore, to get ph:

    pH = 9.32 + log (0.230 mol + 0.030 mol) / (0.250 mol - 0.030 mol)

    pH = 9.32 + 0.0726

    pH = 9.393
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