Question

A buffer solution with pH 9 is to be prepared by mixing $ N{{H}_{4}}Cl $ and $ N{{H}_{4}}OH $ . Calculate the number of moles of $ N{{H}_{4}}Cl $ that should be added to 1 L of $ 1.0\text{ }M\text{ }N{{H}_{4}}OH $ .

• A. 3.4
• B. 2.6
• C. 1.5
• D. 1.99

Answer 1

Answer: (D)

$ pOH=-\log {{K}_{b}}+\log \left[ \frac{salt}{base} \right] $
$ [14-pH]=-\log [1.8\times {{10}^{-5}}]+\left[ \frac{salt}{1.0} \right] $
$ 5=4.7+\log \left[ \frac{salt}{1.0} \right] $
$ \log \left[ \frac{salt}{1.0} \right]=5-4.7=0.3 $
$ [salt]=antilog\text{ }0.3 $
$ [salt]=1.995 $