# Question #a18c9

May 20, 2017

The mass loss must represent $C {O}_{2}$; and thus we get $8.43 \cdot g$ magnesium carbonate, and $6.03 \cdot g$ $M g O$.

#### Explanation:

The mass loss must represent $C {O}_{2}$. Why? Because carbonates are KNOWN to undergo thermal decomposition according to the following rxn:

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

And so ..........................

$\text{moles of carbon dioxide "-=" moles of magnesium carbonate}$

$\text{Moles of carbon dioxide} = \frac{4.4 \cdot g}{44.01 \cdot g \cdot m o {l}^{-} 1} = 0.0100 \cdot m o l$,

which constitutes a mass of $0.0100 \cdot m o l \times 84.31 \cdot g = 8.43 \cdot g$ WITH RESPECT TO $\text{magnesium carbonate} .$

The balance, $\left(12.46 - 8.43\right) \cdot g = 6.03 \cdot g$ WITH RESPECT TO $\text{magnesium oxide}$.