**maximum buffering capacity: pH = pK**_{a}

**buffering range: pH = pKa ± 1**

$\overline{){{\mathbf{pK}}}_{{\mathbf{a}}}{\mathbf{}}{\mathbf{=}}{\mathbf{}}{\mathbf{-}}{\mathbf{log}}{\mathbf{}}{{\mathbf{K}}}_{{\mathbf{a}}}}$

a)

${\mathbf{pK}}_{\mathbf{a}}\mathbf{}\mathbf{=}\mathbf{}\mathbf{-}\mathbf{log}(1.0\times {10}^{-3})$** = 3.00**

buffering range: 2.oo to 4.00

b)

${\mathbf{pK}}_{\mathbf{a}}\mathbf{}\mathbf{=}\mathbf{}\mathbf{-}\mathbf{log}\mathbf{(}\mathbf{1}\mathbf{.}\mathbf{0}\mathbf{\times}{\mathbf{10}}^{\mathbf{-}\mathbf{6}}\mathbf{)}$** = 6.00**

buffering range: 5.00 to 7.00

c)

${\mathbf{pK}}_{\mathbf{a}}\mathbf{}\mathbf{=}\mathbf{}\mathbf{-}\mathbf{log}\mathbf{(}\mathbf{1}\mathbf{.}\mathbf{3}\mathbf{\times}{\mathbf{10}}^{\mathbf{-}\mathbf{5}}\mathbf{)}$** = 4.87**

buffering range: 3.87 to 5.87

Which weak acid would be best to use when preparing a buffer solution with a pH of 8.20?

a) An acid with K_{a} = 1.0 x10^{-3 }M

b) An acid with K_{a }= 1.0x1O^{-6} M

c) An acid with K_{a} = 1.3x10^{-5} M

d) An acid with K_{a} = 6.6 x10^{-9} M

e) An acid with K_{a} = 4.0 X 10^{-10} M

f) An acid with K_{a} = 7.9 X 10^{-5} M

Frequently Asked Questions

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