Question

Joseph Priestley is credited with the discovery of oxygen. He pro- duced O2 by heating mercury(II) oxide, HgO, to decompose it into its elements. How many moles of oxygen could Priestley have pro- duced if he had decomposed 517.84 g of mercury oxide?

Answer 1

Answer: 1.2 moles

Explanation:

According to the law of conservation of mass, mass can neither be created nor be destroyed. Thus the mass of products has to be equal to the mass of reactants. The number of atoms of each element has to be same on reactant and product side. Thus chemical equations are balanced.

$2HgO\rightarrow 2Hg+O_2$

$\text{Number of moles}=\frac{\text{Given mass}}{\text{Molar mass}}$

$\text{Number of moles of mercury oxide}=\frac{517.84g}{216.59g/mol}=2.4moles$

According to stoichiometry:

2 moles of $HgO$ gives 1 mole of $O_2$

Thus 2.4 moles of $HgO$ will give=$\frac{1}{2}\times 2.4=1.2moles$ of $O_2$

Thus 1.2 moles of oxygen are produced.