Question

$0.4$ g of polybasic acid, $H_{n}A$ (all the hydrogens are acidic) requires $0.5$ g of $NaOH$ for complete neutralization.
The number of replaceable hydrogen atoms and the molecular weight of $A$ would be respectively : (molecular weight of acid $=96$ g/mol)

• A. $2,94$
• B. $1,95$
• C. $3,93$
• D. $4,92$

Answer 1

The correct option is C $3,93$

Given reaction is a neutralisation reaction.
Therefore, mlliequivalents of acid $=$ milliequivalents of Base
$\Rightarrow \frac{0.4}{\frac{Mw}{n}}\times 1000=\frac{0.5}{\frac{40}{1}}\times 1000$
$\Rightarrow n=3$

$H_{n}A\equiv 96\Rightarrow A=96-3\times 1=93$

Hence, the number of replaceable hydrogen atoms is $3$ and the molecular weight of $A$ is $93$ g/mol.