Question

$0.05$M ammonium hydroxide solution is dissolved in $0.001$M ammonium chloride solution. What is the $O{H}^{-}$ ion concentration of this solution? $K_b\left(N{H}_{4}OH\right)=1.8\times {10}^{-5}$.

• A. $3.0\times {10}^{-3}$
• B. $9.0\times {10}^{-4}$
• C. $9.0\times {10}^{-3}$
• D. $3.0\times {10}^{-4}$

Answer 1

The correct option is B $9.0\times {10}^{-4}$

$pOH$ of basic buffer $=p{k}_b+\log \frac{\left[salt\right]}{\left[base\right]}$

$p{k}_b=5-\log 1.8=4.74$

$pOH=4.74+\log \left(\frac{0.001}{0.050}\right)=4.74-\log 50=4.74-\log 5-1=3.05$

$\left[O{H}^{-}\right]=9\times {10}^{-4}$