Question

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

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

Answer 1

The correct option is B $0.0005N_A$

1 millimole $={10}^{-3}$ moles

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 0.5 millimoles will be
$=0.5\times {10}^{-3}{N}_A$
$=0.0005N_A$