form 4 chemistry ex

Consider the thermal decomposition of 10 g of potassium chlorate:
2KClO3 → 2KCl + 3O3
Mole ratio KClO3 : O2 = 2 : 3

Molar mass of KClO3 = 39 + 35.5 + 16x3 = 122.5 g/mol
No. of moles of KClO3 used = 10/122.5 = 0.08163 mol
No. of moles of O2 formed = 0.08163 x (3/2) = 0.1224 mol

Consider the thermal decomposition of HgO:
2HgO → 2Hg + O2
Mole ratio HgO : O2 = 2 : 1

No. of moles of O2 formed = 0.1224 mol
No. of moles of HgO used = 0.1224 x 2= 0.2448 mol
Molar mass of HgO = 200.6 + 16 = 216.6 g/mol
Mass of HgO used = 0.2448 x 216.6 = 53 g