Question

$0.16 \,g$ of dibasic acid requires $25 \,mL$ decimolar $NaOH$ solution for complete neutralisation. The molecular mass of the acid is

• A. 256
• B. 64
• C. 32
• D. 128

Answer 1

Answer: (D)

$0.16 \,g$ of dibasic acid is neutralised by
$=25 \,mL$ of $0.1\, M \,NaOH$
$H _{2} X +2 NaOH = Na _{2} X + H _{2} O$
Millimoles of acid $=\frac{1}{2} \times$ millimoles of $NaOH$
$=\frac{1}{2} \times 25 \times 0.1=1.25$
$\because$ Millimoles $=\frac{ W ( mg )}{ \text{mol . mass }}$
$\therefore $ Mol. mass $=\frac{ W ( mg )}{\text { millimoles }}$
$=\frac{0.16 \times 1000}{1.25}=128$