Pearson Edexcel International GCSE in Chemistry · 4CH1 · Free · no account needed
Reacting Masses and Percentage Yield — exam questions
10 original Incandio exam-style questions on Reacting Masses and Percentage Yield, 21 marks, about 21 minutes of writing. Each one carries the command word, the tariff and the specification statement it assesses, exactly as a paper presents them. This is an original Incandio practice question, written to reflect the structure and demands of the qualification. It is not an official Pearson Edexcel past-paper question.
This is the practice set for Reacting Masses and Percentage Yield — the lesson that teaches it. Read the lesson first if the idea is new; come here when you want to find out whether you can turn it into marks. Completely free, no account needed to read.
What these questions ask of you
5 command words run through this set, and on Pearson Edexcel International GCSE Chemistry each one means something precise. Answering the wrong command is the commonest way a candidate who understands the lesson still loses the mark.
- Which (1 mark)
- one option chosen from the set given
- State what is meant by (1–2 marks)
- the definition
- Calculate (1–4 marks)
- a numerical answer with working, to the stated precision
- Give (1–2 marks)
- a short factual answer — the most common chemistry command
- Suggest (1–3 marks)
- a plausible answer applying taught chemistry to an unfamiliar substance
Assessed on Paper 1 (4CH1/1C) and Paper 2 (4CH1/2C), against AO1, AO2, AO3.
Where these sit in the specification
Pearson Edexcel International GCSE Chemistry (4CH1) — statements 1.30 · 1.29. Incandio is aligned to this specification; it is not published by, endorsed by or affiliated with Pearson, and it reproduces none of Pearson's wording.
The 10 questions
Answer them on paper, then open the lesson's exam practice to have them marked. The mark scheme, the accepted and rejected answers and the annotated model answer are in Incandio and are not printed here — an answer beside its question is not practice.
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Calcium carbonate decomposes when heated: CaCO₃ → CaO + CO₂. A student heated 25.0 g of calcium carbonate strongly until its mass stopped changing, and obtained 12.6 g of calcium oxide.
Relative atomic masses — H = 1, C = 12, O = 16, Mg = 24, S = 32, Ca = 40, Cu = 64, Zn = 65
(a)
(2)Calculate
Calculate the number of moles of calcium carbonate heated.
Calcium carbonate decomposes when heated: CaCO₃ → CaO + CO₂. A student heated 25.0 g of calcium carbonate strongly until its mass stopped changing, and obtained 12.6 g of calcium oxide.
Relative atomic masses — H = 1, C = 12, O = 16, Mg = 24, S = 32, Ca = 40, Cu = 64, Zn = 65
(b)
(3)Calculate
Calculate the theoretical yield of calcium oxide from this quantity of calcium carbonate.
Calcium carbonate decomposes when heated: CaCO₃ → CaO + CO₂. A student heated 25.0 g of calcium carbonate strongly until its mass stopped changing, and obtained 12.6 g of calcium oxide.
Relative atomic masses — H = 1, C = 12, O = 16, Mg = 24, S = 32, Ca = 40, Cu = 64, Zn = 65
theoretical yield of calcium oxide = ............................ g
(c)
(2)Calculate
Calculate the percentage yield the student obtained. Give your answer to 3 significant figures.
Calcium carbonate decomposes when heated: CaCO₃ → CaO + CO₂. A student heated 25.0 g of calcium carbonate strongly until its mass stopped changing, and obtained 12.6 g of calcium oxide.
Relative atomic masses — H = 1, C = 12, O = 16, Mg = 24, S = 32, Ca = 40, Cu = 64, Zn = 65
............................ %
(d)
(2)Suggest
Suggest why the student's yield was below 100% even though the reaction went to completion.
Calcium carbonate decomposes when heated: CaCO₃ → CaO + CO₂. A student heated 25.0 g of calcium carbonate strongly until its mass stopped changing, and obtained 12.6 g of calcium oxide.
Relative atomic masses — H = 1, C = 12, O = 16, Mg = 24, S = 32, Ca = 40, Cu = 64, Zn = 65
(Total for Question 1 = 9 marks)
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(1)Which
Which value can a percentage yield never exceed?
Value A 50% B 75% C 100% D 200% (Total for Question 2 = 1 mark)
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(1)State what is meant by
State what is meant by the theoretical yield of a reaction.
(Total for Question 3 = 1 mark)
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(4)Calculate
Calculate the mass of magnesium oxide formed when 6.0 g of magnesium burns completely in oxygen. The equation is 2Mg + O₂ → 2MgO.
Relative atomic masses — H = 1, C = 12, O = 16, Mg = 24, S = 32, Ca = 40, Cu = 64, Zn = 65
mass of magnesium oxide formed = ............................ g
(Total for Question 4 = 4 marks)
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(2)Calculate
A reaction has a theoretical yield of 8.40 g and 6.72 g is actually obtained. Calculate the percentage yield.
percentage yield = ............................ %
(Total for Question 5 = 2 marks)
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(2)Give
Give two reasons why the percentage yield of a reaction carried out in a school laboratory is usually well below 100%.
(Total for Question 6 = 2 marks)
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(2)Suggest
A student calculates a percentage yield of 106% for a salt she has prepared and dried. Suggest what is most likely to have happened.
(Total for Question 7 = 2 marks)
Have them marked, then defend the answer
Practice tells you the mark; teaching it back tells you whether you understand it. On Incandio a topic counts as mastered only once you have taught it and defended it.
- Mark these questions — 10 questions, marked on Incandio against the authored scheme, with the mistake you actually made named.
- Teach it — explain Reacting Masses and Percentage Yield to Ember, an AI pupil who does not have it yet and asks the awkward question.
- Defend it — argue it against John Dalton over three rounds, marked against descriptors you can read first.
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Back to the lesson
- Reacting Masses and Percentage Yield — How much product a reaction should give, how much it actually gives, and why the two are never the same.
- All of Incandio Chemistry · Incandio Exam Practice