Question

The molecular mass of an organic acid was determined by the study of its barium salt. The barium salt contains two moles of water of hydration per $B{a}^{+2}$ ion. $2.562$g of this salt reacts completely with $30$ ml of $0.2$ $M{H}_{2}S{O}_4$ to produce $BaS{O}_4$ and the acid. The acid is monobasic.

What is a molecular mass of anhydrous acid?

$x$ M solution represent that there is $x$ mole solute per liter of solution (atomic mass of $Ba=$ $137$).

• A. $128$ g/mole
• B. $132$ g/mole
• C. $156$ g/mole
• D. $168$ g/mole

Answer 1

The correct option is A $128$ g/mole

The balanced chemical equation is $(RCO{O}^{-}{)}_{2}B{a}^{2+}.2H_{2}O+H_{2}S{O}_4\to BaS{O}_4+2RCOOH+2H_{2}O$
$30$ ml of $0.2$ M sulfuric acid correspond to $\frac{0.2\times 30}{1000}=0.006moles.$
They will react with $0.006$ moles ($2.562$ g) of hydrated salt.
The molecular weight of the hydrated salt is $\frac{2.562}{0.006}=427g$
The molecular weight of anhydrous salt is $\frac{427-137-2\times 18+2}{2}=128g/mol$.