Practise Amounts of substances in equations. 14 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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In a reaction represented by the general equation X + 3Y → 2Z, the balancing numbers give the ratio of moles that react and are produced. How many moles of Y react with 6 mol of X?
18 mol
Sample questions
Written for this site in the style of AQA exam questions. They are not taken from real past papers.
Question 1Easy4 marks
Sodium reacts with water: 2Na + 2H2O → 2NaOH + H2
(a) What does the equation show? Tick (✓) one box.[1]
2 g of sodium reacts with 2 g of water.
2 moles of sodium react with 2 moles of water.
2 moles of sodium produce 2 moles of hydrogen.
1 g of hydrogen is produced.
(b) How many moles of sodium hydroxide are produced when 0.4 mol of sodium reacts?[1]
(c) How many moles of hydrogen are produced when 0.4 mol of sodium reacts?[1]
(d) How many moles of water react with 3 mol of sodium?[1]
Show the answer and mark scheme
(a)Answer: 2 moles of sodium react with 2 moles of water.
(b)Answer: 0.4 mol
0.4 (mol)
(c)Answer: 0.2 mol
0.2 (mol)
(d)Answer: 3 mol
3 (mol)
Question 2Medium7 marks
Zinc carbonate decomposes when it is heated: ZnCO3 → ZnO + CO2 Relative atomic masses (Ar): C = 12, O = 16, Zn = 65
(a) Calculate the relative formula mass (Mr) of zinc carbonate.[1]
(b) Calculate the mass of zinc oxide produced when 6.25 g of zinc carbonate decomposes completely.[3]
(c) Calculate the mass of zinc carbonate needed to produce 8.8 g of carbon dioxide.[3]
Show the answer and mark scheme
(a)Answer: 125
125
(b)Answer: 4.05 g
moles of ZnCO3 = 6.25 ÷ 125 = 0.05
moles of ZnO = 0.05 / Mr of ZnO = 81
mass = 0.05 × 81 = 4.05 (g)
(c)Answer: 25 g
moles of CO2 = 8.8 ÷ 44 = 0.2
moles of ZnCO3 = 0.2
mass = 0.2 × 125 = 25 (g)
Question 3Hard6 marks
The thermite reaction is used to weld railway lines together. Aluminium reacts with iron(III) oxide to produce molten iron: Fe2O3 + 2Al → Al2O3 + 2Fe Relative atomic masses (Ar): O = 16, Al = 27, Fe = 56
(a) One weld needs 1.12 kg of iron. Calculate the minimum mass of aluminium needed. Give your answer in kg.[4]
(b) Calculate the mass of iron(III) oxide that reacts to produce 1.12 kg of iron. Give your answer in kg.[2]