Question

Magnesium and oxygen combine in the ratio of 3 : 2 by mass to form magnesium oxide. What mass of oxygen gas would be required to react completely with 24 g of magnesium?

Answer 1

Magnesium and oxygen combine to form magnesium oxide in the ratio 3:2
It follows the law of constant proportion,
3 g of magnesium combines with 2 g of oxygen
So,
24 g of magnesium combines = $$\begin{gathered} \frac{2}{3}\times 24\mathrm{g}\mathrm{of}\mathrm{oxygen} \\ =16\mathrm{g}\mathrm{of}\mathrm{oxygen} \end{gathered}$$

So, 24 g of magnesium requires 16 g of oxygen to react completely.