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19 April, 09:17

A buffer contains 0.18 mol of propionic acid (C2H5COOH) and 0.26 mol of sodium propionate (C2H5COONa) in 1.20 L. What is the pH of this buffer?

What is the pH of the buffer after the addition of 0.02 mol of NaOH?

What is the pH of the buffer after the addition of 0.02 mol of HI?

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  1. 19 April, 10:26
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    1) pH = 5.05

    2) pH = 5.13

    3) pH = 4.97

    Explanation:

    Step 1: Data given

    Number of moles of propionic acid = 0.18 moles

    Number of moles sodium propionate = 0.26 moles

    Volume = 1.20 L

    Ka = 1.3 * 10^-5 → pKa = 4.989

    Step 2: Calculate concentrations

    Concentration = moles / volume

    [acid] = 0.18 / 1.2 = 0.150 M

    [salt] = 0.26 / 1.3 = 0.217 M

    pH = 4.89 + log (0.217/0.150) = 5.05

    What is the pH of the buffer after the addition of 0.02 mol of NaOH?

    moles acid = 0.18 - 0.02 = 0.16

    [acid] = 0.16 / 1.2=0.133 M

    moles salt = 0.26 + 0.02 = 0.28

    [salt] = 0.28 / 12=0.233

    pH = 4.89 + log 0.233 / 0.133 = 5.13

    What is the pH of the buffer after the addition of 0.02 mol of HI?

    moles acid = 0.18 + 0.02 = 0.20 moles

    [acid] = 0.20 / 1.2 = 0.167 M

    [salt] = 0.26 - 0.02 = 0.24 moles

    [salt] = 0.24 / 1.2 = 0.20 M

    pH = 4.89 + log 0.20 / 0.167 = 4.97
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