Question

Find the percentage mass of water in Epsom salt $MgS{O}_4.7H_{2}O.$

Answer 1

Relative molecular mass of $MgS{O}_4.7H_{2}O$
$=24+32+(16\times 4)+7(2+16)$
$=24+32+64+126=246$
$26g$ of Epsom salt contains $126g$ of water of crystallisation.
Hence, $100g$ of Epsom salt contains $100\times 126/246$
The $\%$ of $H_{2}O$ in $MgS{O}_4.7H_{2}O=51.2$