Using the K_a values in the table below, calculate the pH of a buffer that conta

Question

Using the K_a values in the table below, calculate the pH of a buffer that contains the given concentrations of a weak acid and its conjugate base. 0.36 M NaHCO_3 and 0.30 M Na_2 CO_3 pH = Calculate the pH of an acetic acid/acetate buffer in which the concentration of acetic acid is always 0.34 M, but the concentration of sodium acetate (NaCH_3 COO) corresponds to the following value: 0.32 M. (K_a for CH_3 COOH is 1.8 times 10^-5.) Report your answer to three significant figures. The optimum pH of a swimming pool is 7.58. Calculate the value of [H_3 O^+] and [OH^-] at this pH. [H_3 O^+] = times 10 (select) M [OH^-] = times 10 (select) M

Explanation / Answer

47. pH Of acidic buffer = pka + log(salt/acid)

     pka = -logka

          = -log(5.6*10^-11) = 10.25

pH = 10.25+log(0.3/0.36)

     = 10.17

1.

pka of aceticacid = -log(1.8*10^-5) = 4.74

pH Of acidic buffer = pka + log(salt/acid)

pH = 4.74 + log(0.32/0.34)

    = 4.71

2. pH = 7.58

[H3O+] = 10^-pH

        = 10^-7.58 = 2.63*10^-8 M

[OH^-] = KW/[H3O+] = 1*10^-14/(2.63*10^-8)

         = 3.8*10^-7 M

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