Preparation of oxygen in the laboratory can be done by decomposing of potassium chlorate.
Potassium chlorate decomposes, on strong heating, to form potassium chloride and oxygen.
This decomposition of potassium chlorate can be achieved at lower temperatures when the catalyst manganese (IV) oxide is used.
The decomposition reaction of potassium chlorate is as follows:
Heat
2KClO₃ ----------------------------> 2KCl + 3O₂
The mole ratio for the reaction is 2:2:1 meaning, two moles of KClO₃ yields 2 moles of KCl and 3 moles of O₂
Calculate the moles of oxygen from the 6.72 dm³ given
1 dm³ = 1 liter
6.72 dm³ = 6.72 liters of oxygen
Using the ideal gas law, which states that 1 mole of an ideal gas occupies 22.4 liters by volume we can calculate the moles of oxygen as follows:
If 22.4 liters = 1 mole
Then 6.72 liters = 1 × 6.72/ 22.4
= 0.3 moles
From the equation above we found the mole ratio for the equation to be 2:2:1
That means, for 0.3 moles of oxygen to be liberated, we will need 0.3 × 2 = 0.6 moles of KClO₃
Use the 0.6 moles of KClO₃ to find the mass required
Moles = mass / molar mass and,
mass = molar mass × moles
molar mass of potassium chlorate is 122.5 g/mol (given) and moles is 0.6(calculated)
Therefore mass of KClO₃ required = 122.5 g/mol x 0.6 moles
= 73.5 g
Therefore you need 73.5 g of potassium chlorate to liberate 6.72 dm³ of oxygen.