Question

A solution is $0.01M$ in $(N{H}_4{)}_{2}S{O}_4$ and $0.02M$ in $N{H}_{4}OH$ $(K_b=2\times {10}^{-5})$. Which of the following is(are) true about this solution?

• A. The solution is a buffer
• B. pH of this solution is $(9+2log2)$.
• C. pH of this solution is $(9+log2)$.
• D. Adding water to the above solution will increase pH.

Answer 1

Answer: (A), (C)

The correct options are
A The solution is a buffer
C pH of this solution is $(9+log2)$.

The given solution shows buffer action as itis a mixture of a weak base and its salt.The pH of this buffer can be calculated by using the Henderson-Hesselbalch equation.
i.e., $pH=p{K}_w-pOH=14-(p{K}_b+log\frac{\left[salt\right]}{\left[base\right]})$
$\Rightarrow pH=14-[-log(2\times {10}^{-5})+log(\frac{2\times 0.01}{0.02}\left)\right]$
$\Rightarrow pH=14-5+log2=9+log2$