Calculate the mass of o2 produced if 3.450g potassium chlorate is completely decomposed by heating in presence of a catalyst (manganese dioxide)

1) Balanced chemical reaction

2 KCl O3 ---> 2 KCl + 3 O2

2) stoichiometry

2 mol of KCl O3 / 3 mol O2

atomic and molecular masses

K: 39 g/mol
Cl: 35.5 g/mol
O: 16 g/mol

KClO3: 39 + 35.5 + 3*16 = 122.5 g/mol
O2: 2*16 = 32 g/mol

ratio of masses: 2* 122.5 g of K Cl O3 / 3* 32 g O2

4) final calculations

3.450 g KClO3 * 96 g O2 / 245 g KClO3 = 1.352 g O2

5)  1.352 gO2