Question

The sum of $pH$ and $p{K}_b$ for a basic buffer solution is $13$. The ratio of the concentration of the base to that of the salt is:

• A. $10$
• B. $1$
• C. $0.05$
• D. $0.1$
• E. $20$

Answer 1

The correct option is D $0.1$

From $pOH=p{K}_b=-\log \frac{\left[base\right]}{\left[salt\right]}$
$14-pH=p{K}_b-\log \frac{\left[base\right]}{\left[salt\right]}$
$\therefore 14=pH+p{K}_b-\log \frac{\left[base\right]}{\left[salt\right]}$
or $14=13-\log \frac{\left[base\right]}{\left[salt\right]}$
$\log \frac{\left[base\right]}{\left[salt\right]}=13-14=-1$.
$\therefore \frac{\left[base\right]}{\left[salt\right]}=antilog(-1)=0.1$.