Question

A mixture of KClO3 and KCl with a mass of 0.950 g was heated to produce O2. After heating, the mass of residue was 0.840 g. Assuming all the KClO3 decomposed to KCl and O2, calculate the mass percent KClO3 in the original mixture.

Answer 1

Total mass of the mixture of KCl and KClO₃ = 0.950 g.

Now, the mixture was heated so that KClO₃ converted to KCl and released O₂ gas.

Now, after heating, the mass of the residue = 0.840 g

Hence, the mass of oxygen that must have escaped as gas = 0.950 g - 0.840 g = 0.110 g

It is being assumed that all the KClO₃ is being decomposed.

The reaction of decomposition of KClO₃ can be written as

Hence, two moles of KClO₃ produces three moles of O₂ gas.

Molar mass of O₂ = 32.0 g/mol

Hence, number of moles of O₂ released can be calculated as

Now, from the balanced reaction, we have seen that 2 moles of KClO₃ produces three moles of O₂.

Hence, the number of moles of KClO₃ that has produced of O₂ can be calculated as

Molar mass of KClO₃ = 122.55 g/mol

Hence, the mass of KClO₃ that was present in the mixture can be calculated as

Hence, the percent KClO₃ in the mixture can be calculated as

Hence, the mass percent of  KClO₃ in the mixture is 29.56%.