Lawrie Ryan and Roger Norris Solutions for Chapter: Further Aspects of Equilibria, Exercise 11: Question

Calculate the pH of the following buffer solution:

$0.0500 \mathrm{mol} {\mathrm{dm}}^{-3}$ methanoic acid and $0.100 \mathrm{mol} {\mathrm{dm}}^{-3}$ sodium methanoate. (${\mathrm{K}}_{\mathrm{a}}$ of methanoic acid = $1.60 \mathrm{x} {10}^{-4} \mathrm{mol} {\mathrm{dm}}^{-3}$)

Calculate the pH of the following buffer solution:

$0.0100 \mathrm{mol} {\mathrm{dm}}^{-3}$ benzoic acid and $0.0400 \mathrm{mol} {\mathrm{dm}}^{-3}$ sodiumbenzoate. (${\mathrm{K}}_{\mathrm{a}}$ of benzoic acid = $6.3 \mathrm{x} {10}^{-5} \mathrm{mol} {\mathrm{dm}}^{-3}$)

How many moles of sodium ethanoate must be added to $1.00 {\mathrm{dm}}^{-3}$ of $0.100 \mathrm{mol} {\mathrm{dm}}^{-3}$ ethanoic acid to produce a buffer solution of $\mathrm{pH} 4.90$? (${\mathrm{K}}_{\mathrm{a}}$ of ethanoic acid = $1.74 \mathrm{x} {10}^{-5} \mathrm{mol} {\mathrm{dm}}^{-3}$)

What is the $\mathrm{pH}$ of a buffer solution made by mixing $100 {\mathrm{cm}}^3$ of $0.1 \mathrm{mol} {\mathrm{dm}}^{-3}$ methanoic acid with $50 {\mathrm{cm}}^3$ $0.1 \mathrm{mol} {\mathrm{dm}}^{-3}$ sodium methanoate? ${\mathrm{K}}_{\mathrm{a}} \left(\mathrm{HCOOH}\right) = 1.6 \mathrm{x} {10}^{-4}$