Question

The molecular mass of organic acid was determined by the study of its barium salt $4.290$ g of salt was quantitatively converted to the free acid by the reaction with $21.64$ ml of $0.477$ $M{H}_{2}S{O}_4$. The barium salt was found to have two moles of water of hydration per $B{a}^{2+}$ ion and acid is monobasic. What is the molecular weight of anhydrous acid?

• A. 130
• B. 142
• C. 100
• D. 110

Answer 1

The correct option is A 130

Weight of salt $=4.290g$

Volume of acid $=21.64$

molarity $=0.477M$

Eqn : ${\left(R{100}^{-}\right)}_2{Ba}^{2+}.2H_{2}O+H_2{SO}_4\to {BaSO}_4+2R\left(60\right)+{2H}_{2}O$

$21.64$ of $0.477M$ $H_2{SO}_4=\frac{0.477\times 21.64}{1000}=0.01$ moles

they react with $0.010$ moles $\left(1.290g\right)$ of salt.

$\therefore$ molecular weight $=\frac{4.290}{0.01}=429g$

Molecular weight of anhydrous acid is

$(429-127-2\times 18+2)\times \frac{1}{2}$

$\downarrow$ $\downarrow$ $\downarrow$

$Ba$ $H_{2}O$ $H^{+}$

$=129g$