Question

If $2$ millimoles of hydrated copper sulphate salt $\left(CuS{O}_4.5H_{2}O\right)$ is heated to dryness, then calculate the obtained mass of anhydrous copper sulphate salt.
(Given: molar mass of $Cu=63.5\text{g/mol}$)

• A. $0.32\text{g}$
• B. $0.32\text{mg}$
• C. $0.49\text{g}$
• D. $0.49\text{mg}$

Answer 1

The correct option is A $0.32\text{g}$

The molar mass of hydrated copper sulphate salt $\left(CuS{O}_4.5H_{2}O\right)$$=63.5+32+16\times 4+5\times 18=249.5\text{g/mol}$

$CuS{O}_4.5H_{2}O\to CuS{O}_4+5H_{2}O$
On heating, we will get anhydrous copper sulphate salt i.e $CuS{O}_4$

The molar mass of anhydrous copper sulphate salt$=63.5+32+16\times 4=159.5\text{g/mol}$

As per the reaction, 1 mol of $CuS{O}_4.5H_{2}O$ will give 1 mole of $CuS{O}_4$

2 millimoles of hydrated copper sulphate salt will give 2 millimoles of anhydrous copper sulphate.

So, the mass of anhydrous copper sulphate salt
$=159.5\times 2\times {10}^{-3}=0.319\text{g}$