Question

1g1g of Magnesium burnt with 0.5g of oxygen in closed vessel. The reactant remaining unreacted is:

• A. $0.20g$ of $Mg$
• B. $0.1g$ of $Mg$
• C. $0.25g$ of $Mg$
• D. $0.1667g$ of $Mg$

Answer 1

Answer: (D)

$0.1667g$ of $Mg$

Given that

Mass of $Mg\left(W_{Mg}\right)=1g$

Mass of $O_2\left(W{O}_2\right)=0.5g$

Now, $Mg+\frac{1}{2}{O}_2\to MgO$

$24g$ $8g$

Now, $Mg\to \frac{W_{Mg}}{24}=\frac{1}{24}\approx 0.04167$

$O_2\to \frac{W_{O_2}}{8}=\frac{0.5}{8}\approx 0.0625$

Since, $0.0625>0.04167$

$\therefore O_2$ is in excess and Mg is limiting reagent.

Now,

$24g$ of $Mg\stackrel{rect}{\to }8g$ of $O_2$

$1g$ of $Mg\stackrel{rect}{\to }\frac{8}{24}g$ of $O_2$

$=\frac{1}{3}g$ of $O_2$

$\therefore$ Mass of $O_2$ left $=0.5g-\frac{1}{3}g$

$=0.1667g$

$Option\left(D\right)0.1667g$