Question

A sample of a hydrate of barium chloride weighing 61 g was heated until all the water of hydration is removed. The dried sample weighed 52 g. The formula of the hydrated salt is : (atomic mass, Ba = 137 amu, Cl = 35.5 amu)

• A. BaCl${}_2$.4H${}_2$O
• B. BaCl${}_2$.2H${}_2$O
• C. BaCl${}_2$.H${}_2$O
• D. BaCl${}_2$.3H${}_2$O

Answer 1

The correct option is B BaCl${}_2$.2H${}_2$O

Let the formula of the hydrated salt be $BaC{l}_2.x{H}_{2}O$
$BaC{l}_2.x{H}_{2}O\stackrel{\Delta }{\to }BaC{l}_2.x{H}_{2}O$.

	$BaC{l}_2.x{H}_{2}O$	$BaC{l}_2$
Molar mass (g/mol)	208+18x	208
Mass (g)	61	52

Thus $208=\frac{52}{61}\times (208+18x)$
$244=208+18x$
$36=18x$
$x=2$
Hence, the formula of the hydrated salt is $BaC{l}_2.2H_{2}O$.