An 11.75g sample of a common hydrate of cobalt(II) chloride is heated. After heating 0.0712 mol of anhydrous cobalt chloride remains. What is the formula of the hydrate (Atomic Weight of Co = 58 )

Mol.wt of anhydrous ${\mathrm{CoCl}}_2=58+71=129$
$\therefore$ wt of anhydrous ${\mathrm{CoC\ell }}_2=0.0712\times 129=9.1848$
$\therefore$ wt of water $\Rightarrow 11.75-9.1848=2.5652$
The weight of water that combines with 129 gm of  ${\mathrm{CoCl}}_2$ is 36.02
$\therefore$ Number of water molecules = 2