Question

Which of the following mixture present in water acts as a good buffer?

• A. 0.02 mole HCN, 0.03 mole KCN
• B. 0.03 mole HCN, 0.06 mole KCN
• C. 0.07 mole HCN, 0.06 mole KCN
• D. 0.07 mole HCN, 0.02 mole KCN

Answer 1

The correct option is C

0.07 mole HCN, 0.06 mole KCN

$pH=p{K}_a$+ log$\frac{\left[KCN\right]}{\left[HCN\right]}$

Buffer capacity is maximum if $pH\cong p{K}_a$

i.e. [KCN] $\cong$ [HCN]

$\frac{\left[KCN\right]}{\left[HCN\right]}=\frac{0.07}{0.06}$ = 1.16