Chemistry Question

Question

Potassium nitrate is widely used as a fertilizer because it provides two essential elements, potassium and nitrogen. It is made by mixing potassium chloride and nitric acid in the presence of oxygen according to the equation

4KCl(aq) + 4HNO₃(aq) + O₂(g) --> 4KNO₃(aq) + 2Cl₂(g) + 2H₂O(I)     

How many kilograms of potassium nitrate will be produced from a solution containing 49.8 kg of potassium chloride and one containing 47 kg of nitric acid?  

Answer 1

4KCl(aq) + 4HNO₃(aq) + O₂(g) --> 4KNO₃(aq) + 2Cl₂(g) + 2H₂O(I) ... balanced equation

molar mass KCl = 74.6 g / mole

molar mass HNO₃ = 63.0 g / mole

molar mass KNO₃ = 101.1 g / mole

Find the limiting reactant. One easy way to do this is to divide the moles of each reactant by the corresponding coefficient in the balanced equation. Whichever values is less represents the limiting reactant.

For KCl: 49.8 kg x 1 kmole / 74.6 kg = 0.668 kmole (÷4->0.167)

For HNO₃: 47 kg x 1 kmole / 63.0 kg = 0.746 kmole (÷4->0.187)

Since 0.167 is less than 0.187, KCl is the limiting reactant, and we must then use 0.668 kmoles of KCl to determine the mass of product (KNO₃) formed.

Mass of KNO₃ formed = 0.688 kmol KCl x 4 kmol KNO₃ / 4 kmol KCl x 101.1 kg / kmol KNO₃ = 69.6 kg KNO₃