Calculate how much oxygen can be obtained by decomposition of 63.4 mercury oxide (HgO).

1) Write the reaction equation for the decomposition of mercury oxide and arrange the coefficients:
2HgO = 2Hg + O2
2) Find the amount of mercury oxide: n = m / M = 63.4 / 217 = 0.3 mol (M = 217 g / mol from the periodic table)
3) Let’s make the proportion
0.3 / 2 = x / 1 (2 and 1 are coefficients in the reaction equation)
x = 0.15
4) Find the mass of oxygen: m = M * n = 32 * 0.15 = 4.8 g
Answer: 4.8 g.