Question

To neutralize completely $20\, mL$ of $0.1\, M$ aqueous solution of phosphorus acid $ ({{H}_{3}}P{{O}_{3}}), $ the volume of 0.1 M aqueous KOH solution required is

• A. 20 mL
• B. 30 mL
• C. 40 mL
• D. 50 mL

Answer 1

Answer: (C)

$ {{H}_{3}}P{{O}_{3}} $ is a dibasic acid.
$ {{N}_{1}}{{V}_{1}}(acid)={{N}_{2}}{{V}_{2}}(base) $
$ 0.1\times 2\times 20=0.1\times 1\times {{V}_{2}} $
$ {{V}_{2}}=\frac{0.1\times 2\times 20}{0.1\times 1} $
$ =40\,mL $