Question

$2.6g$ mixture of carbonates of magnesium ( $MgCO_{3}$ ) and calcium ( $CaCO_{3}$ ) is strongly heated to the constant weight of $1.3g$ . The weight of calcium carbonate in the original mixture?

• A. $980mg$
• B. $400mg$
• C. $1.75g$
• D. $0.74g$

Answer 1

Answer: (D)

Suppose weight of $CaCO_{3}=xg.$ Then $\left(MgCO\right)_{3}=\left(\right.2.6-x\left.\right)g$
$CaCO_{3} \rightarrow \underset{100 g}{ \rightarrow }CaO+CO_{2}\Rightarrow xg \rightarrow 0.56xg$
$\underset{84 g}{Mg \left(CO\right)_{3}} \rightarrow \underset{40 g}{MgO + \left(CO\right)_{2}}\Rightarrow \left(\right.2.6-x\left.\right)g \rightarrow \frac{40}{84}\left(\right.2.6-x\left.\right)g$
$0.56x+\frac{40}{84}\left(\right.2.6-x\left.\right)=1.3$ (Given)
$47.04x+104-40x=109.2\Rightarrow 7.04x=5.2\text{ or }x=0.74g$