Question

The composition of residual mixture will be, if $30 g$ of Mg combines with $30 g$ of $O _{2}-$

• A. $40 \,g \,MgO +20 \,g \,O _{2}$
• B. $45 \,g \,MgO +15\, g\, O _{2}$
• C. $50 \,g \,MgO +10 \,g\, O _{2}$
• D. $60 \,g \,MgO$ only

Answer 1

Answer: (C)

$2 Mg + O _{2} \to 2 MgO$

$2 \times 24 \,g \,Mg$ reacts with $O _{2}=32 \,g$

$30\, g\, Mg$ reacts with $O _{2}=\frac{32}{2 \times 24} \times 30=20 \,g$

So, $10\, g\, O _{2}$ will be left unreacted

$Mg$ is the limiting reagent

$2 \times 24\, g\, Mg$ forms $MgO =2 \times 40 \,g$

$30 \,g \,Mg$ forms $MgO =\frac{2 \times 40}{2 \times 24} \times 30=50 \,g$