Potassium nitrate decomposes on heating, producing potassium oxide and gaseous nitrogen and oxygen: 4KNO3(s) →2K2O(s) + 2N2(g) + 5O2(g)

Question

Potassium nitrate decomposes on heating, producing potassium oxide and gaseous nitrogen and oxygen: 4KNO₃(s) →2K₂O(s) + 2N₂(g) + 5O₂(g)

To produce 67.9 kg of O_2, how many

(a) moles of KNO₃ must be heated?

(b) grams of KNO₃ must be heated?

Answer 1

4KNO₃(s) ==> 2K₂O(s) + 2N₂(g) + 5O₂(g) ... balanced equation

We see that 5 moles O₂ are formed from 4 moles of KNO₃

We want to produced 67.9 kg of O₂. So we must first convert this to moles of O₂ as follows:

67.9 kg O₂ x 1000 g/kg x 1 mole O₂/31.98 g = 2123 moles O₂ = 2.12x10³ moles O₂ (3 sig. figs.)

Now we use the mole ratio of KNO₃ to O₂ to find moles of KNO₃ needed...

2120 mol O₂ x 4 mol KNO₃/5 mol O₂ = 1696 moles KNO₃ = 1.70x10³ moles KNO₃ needed

To get g KNO₃, we simply use the molar mass of KNO₃ (101 g/mol) and the # moles.....

1.70x10³ moles KNO₃ x 101 g/mol = 1.72x10⁵ g KNO₃ needed