Question

What mass of oxygen would be produced upon thermal decomposition of 25 g of potassium chlorate (kclo3)? the molecular weight (mw) of potassium chlorate is 122.5 g/mol?

Answer 1

The formula for potassium chlorate is: 2KClO₃ → 2KCl + 3O₂

If moles = mass ÷ molar mass

then moles of KClO₃ = 25 g ÷ [( 39 × 1 ) + ( 35.5 × 1) + ( 16 × 3)] g/mol

= 25 g ÷ ( 122.5 g ) g/mol

= 0.2041 mol


Now the mole ratio of KClO₃ : O₂ is 2 : 3

∴ if moles of KClO₃ = 0.2041 mol

then moles of O₂ = ( 0.2041 mol ÷ 2 ) × 3

= 0.3061 mol


Now since mass = moles × molar mass

∴ the mass of oxygen produced = 0.3061 mol × ( 16 × 2) g/mol
= 9.796 g


∴ the grams of oxygen gas produced when 25 grams of potassium chlorate is decomposed is ~ 9.80 g.