# A mixture of magnesium carbonate and magnesium oxide of mass 12.46*g underwent fierce heating. After heating, there were 8.43*g of salt remaining. What were the masses of magnesium carbonate, and magnesium oxide in the original sample?

May 19, 2017

Well, we use the general decomposition $\left(\text{calcining}\right)$ reaction of metal carbonates.............

#### Explanation:

$M g C {O}_{3} \left(s\right) + \Delta \rightarrow M g O \left(s\right) + C {O}_{2} \left(g\right)$

And we would have to heat the magnesium salt VERY fiercely to get complete decarboxylation.

$\text{Moles of carbon dioxide LOST}$ $=$ $\frac{4.40 \cdot g}{44.01 \cdot g \cdot m o {l}^{-} 1}$

$= 0.010 \cdot m o l$

And therefore in the original mixture there were $0.010 \cdot m o l$ $M g C {O}_{3}$, i.e. a mass of $0.010 \cdot m o l \times 84.31 \cdot g = 8.43 \cdot g$.

The balance of the salt must have $M g O$, which is (reasonably) inert to heating.

$\text{Mass of MgO}$ $=$ $12.46 \cdot g - 8.43 \cdot g = 4.03 \cdot g$.