AQA GCSE Chemistry (8462), Higher tier · Quantitative chemistry › Conservation of mass and chemical measurements
Practise Relative formula mass. 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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Calculate the relative formula mass (Mr) of calcium carbonate, CaCO3.
100
A metal chloride has the formula XCl3. Its relative formula mass is 133.5. Calculate the relative atomic mass of X.
27
A metal, M, forms an oxide with the formula M2O3. The oxide contains 52.9% of M by mass. Relative atomic masses (Ar): O = 16, Al = 27, Cl = 35.5, Cr = 52, Fe = 56 Identify metal M.
aluminium
Calculate the relative formula mass (Mr) of sodium chloride, NaCl.
58.5
Calculate the relative formula mass (Mr) of urea, CO(NH2)2.
60
Sample questions
Written for this site in the style of AQA exam questions. They are not taken from real past papers.
Question 1Easy5 marks
Relative atomic masses (Ar): H = 1, C = 12, O = 16, Mg = 24, Ca = 40
(a) Calculate the relative formula mass (Mr) of calcium carbonate, CaCO3.[2]
(b) Calculate the relative formula mass (Mr) of magnesium hydroxide, Mg(OH)2.[2]
(c) What is meant by the relative formula mass of a compound?[1]
Show the answer and mark scheme
(a)Answer: 100
40 + 12 + (3 × 16)
100
(b)Answer: 58
24 + 2 × (16 + 1)
58
(c)
the sum of the relative atomic masses of the atoms in the numbers shown in the formula
Question 2Medium7 marks
Ammonium sulfate, (NH4)2SO4, and ammonium nitrate, NH4NO3, are both used as fertilisers. Relative atomic masses (Ar): H = 1, N = 14, O = 16, S = 32
(a) Calculate the relative formula mass (Mr) of ammonium sulfate.[2]
(b) Calculate the percentage by mass of nitrogen in ammonium sulfate. Give your answer to 3 significant figures.[2]
(c) The percentage by mass of nitrogen in ammonium nitrate is 35.0%. A farmer needs to add 70 kg of nitrogen to a field. Calculate the mass of ammonium nitrate the farmer needs.[2]
(d) Suggest one reason why the farmer might choose ammonium nitrate rather than ammonium sulfate.[1]
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(a)Answer: 132
(2 × 14) + (8 × 1) + 32 + (4 × 16)
132
(b)Answer: 21.2%
(28 ÷ 132) × 100
21.2 (%)
(c)Answer: 200 kg
70 × (100 ÷ 35.0) / 70 ÷ 0.350
200 (kg)
(d)
ammonium nitrate has a higher percentage of nitrogen (so a smaller mass is needed / less to transport and spread)
Question 3Hard7 marks
The relative formula mass of a compound can be used to work out the relative atomic mass of an unknown element in it. Relative atomic masses (Ar): Li = 7, C = 12, O = 16, Na = 23, Cl = 35.5, K = 39, Rb = 85
(a) A Group 1 metal carbonate has the formula M2CO3. Its relative formula mass is 138. Calculate the relative atomic mass of M and identify M.[3]
(b) A metal chloride has the formula XCl3. Its relative formula mass is 133.5. Calculate the relative atomic mass of X.[2]
(c) Element Z forms an oxide with the formula Z2O5. The relative formula mass of the oxide is 142. Calculate the relative atomic mass of Z.[2]
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(a)Answer:Ar = 39, so M is potassium
mass of the CO3 part of the formula = 12 + (3 × 16) = 60