Question

24 g of magnesium were burned in oxygen. The compound formed had a mass of 40 g. Explain why the mass had gone up.

Answer 1

Answer :

According to the law of conservation of mass, the mass of reactants must be equal to the mass of products.

The balanced chemical reaction is,

$Mg+\frac{1}{2}O_2\rightarrow MgO$

As we know that the molar mass of magnesium is 24 g/mole, the molar mass of $O_2$ is 32 g/mole and the molar mass of magnesium oxide is 40 g/mole.

From the given balanced reaction, we conclude that

As, 1 mole of magnesium react $\frac{1}{2}$ mole of oxygen to give 1 mole of magnesium oxide.

So, the mass of Mg is 24 g, the mass of $O_2=\frac{1}{2}\times 32=16g$ and the mass of MgO is 40 g.

That means 24 g of Mg react with 16 g $O_2$ to give 40 g of MgO.