AQA GCSE Chemistry (8462), Higher tier · Quantitative chemistry › Conservation of mass and chemical measurements
Practise Conservation of mass and balanced equations. 15 exam-style questions 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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Balance the equation for the reduction of iron(III) oxide by carbon monoxide. Fe2O3 + ....CO → ....Fe + ....CO2
Fe2O3 + 3CO → 2Fe + 3CO2
Lithium reacts with water to produce lithium hydroxide (LiOH) and hydrogen. Write a balanced symbol equation for this reaction.
2Li + 2H2O → 2LiOH + H2
Balance the equation. ....NH3 + ....O2 → ....NO + ....H2O
4NH3 + 5O2 → 4NO + 6H2O
Aluminium reacts with iodine to produce aluminium iodide, AlI3. A teacher sealed 2.70 g of aluminium powder and 25.40 g of iodine in a glass tube and warmed it. After the reaction:
all of the iodine had reacted
0.90 g of aluminium had not reacted.
Balance the equation. ....Al + ....I2 → ....AlI3
2Al + 3I2 → 2AlI3
A chemist heated 7.56 g of ammonium dichromate in a sealed container. The products were 4.56 g of Cr2O3 and 0.84 g of N2. Calculate the mass of X produced.
2.16 g
Symbol equations are balanced by changing the numbers written in front of formulae. The small numbers within a formula must never be changed. How many oxygen atoms are shown in the formula 2Fe(OH)3?
6
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 chlorine to produce sodium chloride. 2Na + Cl2 → 2NaCl
(a) Complete the sentence. Tick (✓) one box. The total mass of the products of a chemical reaction is ...[1]
less than the total mass of the reactants.
equal to the total mass of the reactants.
greater than the total mass of the reactants.
half of the total mass of the reactants.
(b) How many chlorine atoms are shown on the left-hand side of the equation?[1]
(c) A teacher reacted 2.30 g of sodium with 3.55 g of chlorine in a fume cupboard. All of the sodium and all of the chlorine reacted. Calculate the mass of sodium chloride produced.[1]
(d) Explain why the mass of sodium chloride produced is equal to the total mass of the sodium and chlorine that reacted.[1]
Show the answer and mark scheme
(a)Answer: equal to the total mass of the reactants.
(b)Answer: 2
2
(c)Answer: 5.85 g
5.85 (g)
(d)
no atoms are lost or made during a chemical reaction
Question 2Medium5 marks
A student investigated the reaction between barium chloride solution and sodium sulfate solution. The student:
poured 25 cm3 of each solution into two separate beakers
placed both beakers on a balance and recorded the total mass
poured one solution into the other and put both beakers back on the balance
recorded the total mass again.
A white solid formed when the solutions were mixed.
(a) Complete the balanced equation for the reaction. BaCl2(aq) + Na2SO4(aq) → BaSO4(s) + ....NaCl(aq)[1]
(b) The total mass at the start was 148.62 g. Predict the total mass at the end. Give a reason for your answer.[2]
(c) In a second experiment, 2.08 g of barium chloride reacted completely with 1.42 g of sodium sulfate to produce 2.33 g of barium sulfate. Calculate the mass of sodium chloride produced.[2]
Show the answer and mark scheme
(a)Answer: 2NaCl
2 (NaCl)
(b)Answer: 148.62 g — no gas is produced, so no products escape
148.62 (g)
no gas is produced / nothing escapes from the beakers (so no atoms are lost)
(c)Answer: 1.17 g
(2.08 + 1.42) − 2.33
1.17 (g)
Question 3Hard7 marks
In the first stage of the manufacture of nitric acid, ammonia reacts with oxygen to produce nitrogen monoxide (NO) and water.
(b) Butane (C4H10) burns completely in oxygen to produce carbon dioxide and water. Write a balanced symbol equation for this reaction.[2]
(c) A liquid fuel, X, burns completely in oxygen. The balanced equation is: X + 3O2 → 2CO2 + 3H2O Deduce the formula of X. Explain how you worked out your answer.[3]
Show the answer and mark scheme
(a)Answer: 4NH3 + 5O2 → 4NO + 6H2O
4NH3, 4NO and 6H2O (in the ratio 2 : 2 : 3)
5O2 with the rest of the equation correct
(b)Answer: 2C4H10 + 13O2 → 8CO2 + 10H2O
correct formulae for all four substances
correctly balanced: 2C4H10 + 13O2 → 8CO2 + 10H2O
(c)Answer: C2H6O (C2H5OH)
products contain 2 carbon atoms and 6 hydrogen atoms (which must come from X)
products contain 7 oxygen atoms but 3O2 provides only 6