Question

$1.00$ g of a hydrated salt contains $0.2014$ g of iron, $0.1153$ g of sulphur, $0.2301$ g of oxygen and $0.4532$ g of water of crystallisation. How much water molecules are present in its empirical formula? $(Fe=56;S=32;O=16)$

Answer 1

Element	Moles	Least ratio
$Fe$	$\frac{0.2014}{56}=0.0036$	$\frac{0.0036}{0.0036}=1$
$S$	$\frac{0.1153}{32}=0.0036$	$\frac{0.0036}{0.0036}=1$
$O$	$\frac{0.2301}{16}=0.0143$	$\frac{0.0143}{0.0036}=3.97\approx 4$
$H_{2}O$	$\frac{0.4532}{18}=0.025$	$\frac{0.025}{0.0036}=6.94\approx 7$

Hence, the empirical formula is $FeS{O}_4\cdot 7H_{2}O$.