Question

A buffer solution with $pH=9$ is to be prepared by mixing $N{H}_{4}CI$ and $N{H}_{4}OH$. Calculate the number of moles of $N{H}_{4}CI$ that should be added to one litre pf $1.0M$ $N{H}_{4}OH$ . $[K_b=1.8\times {10}^{-5}]$

• A. $3.4$
• B. $2.6$
• C. $1.5$
• D. $1.8$

Answer 1

The correct option is D $1.8$

Given $pH=9,pOH=14-9=5$

$pOH=p{K}_b+\log \frac{\left[salt\right]}{\left[base\right]}$

$5=-\log (1.8\times {10}^{-5})+\log \frac{\left[salt\right]}{1.0}=4.745+\log \left[salt\right]$

$⟹\left[salt\right]=1.79\simeq 1.8$

$1.8$ No. of moles of $N{H}_{4}CI$ to be added to $1L$ of $1.0M$ $N{H}_{4}OH.$