Question

Calculate the number of $FeS{O}_4.7H_{2}O$ formula units in $0.2$ millimoles of pure $FeS{O}_4.7H_{2}O$

• A. $0.2N_A$
• B. $0.0002N_A$
• C. $0.002N_A$
• D. $2000N_A$

Answer 1

The correct option is B $0.0002N_A$

We know, $1\text{millimole}={10}^{-3}\text{mol}$
So, $1$ mole of pure $FeS{O}_4.7H_{2}O$ contains $N_A$ number of formula units of $FeS{O}_4.7H_{2}O$.
The number of formula units of pure $FeS{O}_4.7H_{2}O$ in $0.2$ millimoles will be
$=0.2\times {10}^{-3}{N}_A$
$=0.0002N_A$