Question

The composition of residual mixture will be, if $30g$ of Mg combines with $30g$ of $O_2-$

• A. $40gMgO+20g{O}_2$
• B. $45gMgO+15g{O}_2$
• C. $50gMgO+10g{O}_2$
• D. $60gMgO$ only

Answer 1

Answer: (C)

$2Mg+O_2\to 2MgO$

$2\times 24gMg$ reacts with $O_2=32g$

$30gMg$ reacts with $O_2=\frac{32}{2\times 24}\times 30=20g$

So, $10g{O}_2$ will be left unreacted

$Mg$ is the limiting reagent

$2\times 24gMg$ forms $MgO=2\times 40g$

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