Reacting Masses - Worked Example

Step by step video showing you how to do the reacting masses calculations. In these questions, you are given the mass of the limiting reactant and asked to calculate the mass of a product, using the balanced chemical equation.

If you are practising, here are some questions for you to try. Show  your full working out and see if you arrive at the correct answer:

1. 56 grams of water (H2O) react with sodium (Na) to produce sodium hydroxide (NaOH) and hydrogen gas (H2). Calculate the mass of hydrogen produced. The balanced chemical equation for the reaction is: 2Na + 2H2O  2NaOH + H2

Answer: 3.12 grams

2. Calculate the mass of potassium oxide (K2O) produced from 126 grams of potassium (K) reacting with oxygen (O2) in excess. The balanced chemical equation for the reaction is: 4K + O2  2K2O

Answer: 152 g

3. 34 grams of magnesium (Mg) react with chlorine (Cl2), which is in excess. Calculate the mass of magnesium chloride (MgCl2) produced. The balanced chemical equation for the reaction is:
Mg + Cl2  MgCl2

Answer: 140 grams

4. Excess sulfuric acid (H2SO4) reacts with 23 grams of copper oxide (CuO). Calculate the mass of copper sulfate (CuSO4) that would form. The balanced chemical equation for the reaction is:
CuO (s) + H2SO4 (aq) → CuSO4 (aq) + H2O (l)

Answer: 46.1 grams

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