Question

$12.4$ mL of a solution containing $6.0$ g of a dibasic acid in $1$ L was found to be neutralized by $10$ mL of a decinormal solution of NaOH. The molecular weight of the acid is :

• A. 150
• B. 120
• C. 110
• D. 75

Answer 1

The correct option is A 150

10 mL of a decinormal solution of NaOH corresponds to $10mL\times 0.1N=1mmol$ of NaOH.

They will neutralize 0.5 mmol (or $5\times {10}^{-4}$ mol) of dibasic acid.................(1)

Let, M be the molar mass of dibasic acid.

The number of moles of dibasic acid present are $\frac{6.0g}{M}\times \frac{12.4mL}{1000mL}=\frac{0.0744}{M}mol$...................(2)

From (1) and (2),

$\frac{0.0744}{M}=5\times {10}^{-4}$

$M=148.8\simeq 150g/mol$

Thus, the molecular weight of the acid is 150 g/mol.