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14 May, 15:08

Which of the following buffers will be most effective at pH 9.25? Group of answer choices a mixture of 1.0 M HC2H3O2 and 1.0 M NaC2H3O2 (Ka for acetic acid = 1.8 x 10-5) a mixture of 1.0 M NaCN and 1.0 M KCN (Ka for HCN = 4.9 x 10-10) a mixture of 1.0 M HCl and 1.0 M NaCl a mixture of 1.0 M NH3 and 1.0 M NH4Cl (Kb for ammonia = 1.76 x 1

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  1. 14 May, 15:22
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    The most effective buffer at pH 9.25 will be a mixture of 1.0 M NH3 and 1.0 M NH4Cl

    Explanation:

    Step 1: Data given

    pH of a buffer = pKa + log ([A-]/[Ha])

    a mixture of 1.0 M HC2H3O2 and 1.0 M NaC2H3O2 (Ka for acetic acid = 1.8 x 10-5)

    pH = - log (1.8 * 10^-5) + log (1/1)

    pH = - log (1.8 * 10^-5)

    pH = 4.74

    a mixture of 1.0 M NaCN and 1.0 M KCN (Ka for HCN = 4.9 x 10-10)

    pH = - log (4.9 * 10^-10) + log (1/1)

    pH = - log (1.8 * 10^-5)

    pH = 9.30

    a mixture of 1.0 M HCl and 1.0 M NaCl

    The solution made from NaCl and HCl will NOT act as a buffer.

    HCl is a strong acid while NaCl is salt of strong acid and strong base which do not from buffer solutions hence due to HCl PH is less than 7.

    a mixture of 1.0 M NH3 and 1.0 M NH4Cl (Kb for ammonia = 1.76 x 10^-5)

    Ka * Kb = 1*10^-14

    Ka = 10^-14 / 1.76*10^-5

    Ka = 5.68*10^-10

    pH = - log (5.68*10^-10) + log (1/1)

    pH = - log (5.68*10^-10)

    pH = 9.25

    The most effective buffer at pH 9.25 will be a mixture of 1.0 M NH3 and 1.0 M NH4Cl
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