Question

Calculate the number of formula units of $FeS{O}_4\cdot 7H_{2}O$ in $0.5\text{millimoles}$ of pure $FeS{O}_4\cdot 7H_{2}O$.

• A. $0.5N_A$
• B. $0.005N_A$
• C. $0.0005N_A$
• D. $5000N_A$

Answer 1

The correct option is C $0.0005N_A$

$1\text{millimole}={10}^3\text{moles}$
$1\text{mole}$ of pure $FeS{O}_4\cdot 7H_{2}O$ contains $N_A$ number of formula units of $FeS{O}_4\cdot 7H_{2}O$.
The number of formula units of pure $FeS{O}_4\cdot 7H_{2}O$ in $0.5\text{millimoles}$ will be
$=0.5\times {10}^{-3}{N}_A$
$=0.0005N_A$