Practise Limiting reactants. 15 exam-style questions plus unlimited generated ones on this subtopic, at up to four difficulty levels, with full mark schemes and a progress tracker. Free, no account needed.
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Hydrogen reacts with chlorine: H2 + Cl2 → 2HCl In a reactor, 3 mol of hydrogen was mixed with 2 mol of chlorine and the mixture reacted. Which reactant is the limiting reactant?
chlorine
Sample questions
Written for this site in the style of AQA exam questions. They are not taken from real past papers.
Question 1Easy4 marks
In many reactions, one of the reactants is used in excess.
(a) Complete the sentence. Tick (✓) one box. The reactant that is completely used up in a reaction is called the ...[1]
excess reactant.
limiting reactant.
catalyst.
product.
(b) Give one reason why one reactant is often used in excess.[1]
(c) Hydrogen reacts with chlorine: H2 + Cl2 → 2HCl In a reactor, 3 mol of hydrogen was mixed with 2 mol of chlorine and the mixture reacted. Which reactant is the limiting reactant?[1]
(d) How many moles of hydrogen chloride are produced from 3 mol of hydrogen and 2 mol of chlorine?[1]
Show the answer and mark scheme
(a)Answer: limiting reactant.
(b)
to make sure that all of the other reactant is used up / reacts
(c)Answer: chlorine
chlorine / Cl2
(d)Answer: 4 mol
4 (mol)
Question 2Medium6 marks
Zinc reacts with copper(II) sulfate solution: Zn(s) + CuSO4(aq) → ZnSO4(aq) + Cu(s) A student added 1.30 g of zinc powder to a blue solution containing 0.025 mol of copper(II) sulfate. Relative atomic masses (Ar): Cu = 63.5, Zn = 65
(a) Calculate the number of moles of zinc added.[1]
(b) Explain which reactant is the limiting reactant.[2]
(c) Calculate the maximum mass of copper that can be produced.[2]
(d) Suggest what the student would see at the end of the reaction that shows copper(II) sulfate was in excess.[1]
Show the answer and mark scheme
(a)Answer: 0.02 mol
1.30 ÷ 65 = 0.02 (mol)
(b)
zinc and copper(II) sulfate react in a 1 : 1 ratio and there are fewer moles of zinc (0.02 mol) than copper(II) sulfate (0.025 mol)
so zinc is the limiting reactant / copper(II) sulfate is in excess
(c)Answer: 1.27 g
moles of Cu = 0.02
0.02 × 63.5 = 1.27 (g)
(d)
the solution is still (pale) blue
Question 3Hard8 marks
Aluminium reacts with chlorine to produce aluminium chloride: 2Al + 3Cl2 → 2AlCl3 A student reacted 5.4 g of aluminium with 14.2 g of chlorine. Relative atomic masses (Ar): Al = 27, Cl = 35.5
(a) Show that chlorine is the limiting reactant.[3]
(b) Calculate the maximum mass of aluminium chloride that can be produced. Give your answer to 3 significant figures.[3]
(c) Calculate the mass of aluminium left over at the end of the reaction.[2]
Show the answer and mark scheme
(a)
moles of Al = 5.4 ÷ 27 = 0.2
moles of Cl2 = 14.2 ÷ 71 = 0.2
0.2 mol Al would need 0.3 mol Cl2 (ratio 2 : 3) but there is only 0.2 mol Cl2, so chlorine is limiting