Pearson Edexcel International GCSE in Chemistry · 4CH1 · Free · no account needed
Empirical and Molecular Formulae — exam questions
11 original Incandio exam-style questions on Empirical and Molecular Formulae, 24 marks, about 24 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 Empirical and Molecular Formulae — 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
6 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
- Determine (1–4 marks)
- a value reached by combining given data with a method the learner selects
- Explain (2–4 marks)
- the reason, in terms of particles, bonding, energy or equilibrium Misread as: describing the observation without giving the chemistry that causes it
- Calculate (1–4 marks)
- a numerical answer with working, to the stated precision
- 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 1.31 · 1.32 · 1.33 · 1.36. 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 11 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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A student heated 2.24 g of iron wool in a stream of oxygen until it had all reacted. The oxide produced had a mass of 3.20 g.
Relative atomic masses — H = 1, C = 12, N = 14, O = 16, Na = 23, S = 32, Cl = 35.5, Fe = 56, Cu = 64
(a)
(1)Calculate
Calculate the mass of oxygen that combined with the iron.
A student heated 2.24 g of iron wool in a stream of oxygen until it had all reacted. The oxide produced had a mass of 3.20 g.
Relative atomic masses — H = 1, C = 12, N = 14, O = 16, Na = 23, S = 32, Cl = 35.5, Fe = 56, Cu = 64
............................ g
(b)
(2)Calculate
Calculate the number of moles of iron atoms and the number of moles of oxygen atoms present.
A student heated 2.24 g of iron wool in a stream of oxygen until it had all reacted. The oxide produced had a mass of 3.20 g.
Relative atomic masses — H = 1, C = 12, N = 14, O = 16, Na = 23, S = 32, Cl = 35.5, Fe = 56, Cu = 64
(c)
(2)Determine
Determine the empirical formula of the oxide.
A student heated 2.24 g of iron wool in a stream of oxygen until it had all reacted. The oxide produced had a mass of 3.20 g.
Relative atomic masses — H = 1, C = 12, N = 14, O = 16, Na = 23, S = 32, Cl = 35.5, Fe = 56, Cu = 64
(d)
(3)Suggest
Suggest why the student's result would be unreliable if some of the iron wool had not reacted.
A student heated 2.24 g of iron wool in a stream of oxygen until it had all reacted. The oxide produced had a mass of 3.20 g.
Relative atomic masses — H = 1, C = 12, N = 14, O = 16, Na = 23, S = 32, Cl = 35.5, Fe = 56, Cu = 64
(Total for Question 1 = 8 marks)
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(1)Which
A compound has the molecular formula C₆H₁₂O₆. Which is its empirical formula?
Formula A CHO B CH₂O C C₂H₄O₂ D C₆H₁₂O₆ (Total for Question 2 = 1 mark)
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(1)State what is meant by
State what is meant by the empirical formula of a compound.
(Total for Question 3 = 1 mark)
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(3)Determine
A compound contains 3.6 g of carbon, 0.6 g of hydrogen and 4.8 g of oxygen. Determine its empirical formula.
Relative atomic masses — H = 1, C = 12, N = 14, O = 16, Na = 23, S = 32, Cl = 35.5, Fe = 56, Cu = 64
(Total for Question 4 = 3 marks)
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(2)Determine
A compound has the empirical formula CH₂ and a relative molecular mass of 56. Determine its molecular formula.
Relative atomic masses — H = 1, C = 12, N = 14, O = 16, Na = 23, S = 32, Cl = 35.5, Fe = 56, Cu = 64
(Total for Question 5 = 2 marks)
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(3)Determine
A hydrocarbon contains 85.7% carbon by mass, the rest being hydrogen. Determine its empirical formula.
Relative atomic masses — H = 1, C = 12, N = 14, O = 16, Na = 23, S = 32, Cl = 35.5, Fe = 56, Cu = 64
(Total for Question 6 = 3 marks)
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(2)Explain
Explain why two different compounds can have the same empirical formula.
(Total for Question 7 = 2 marks)
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(4)Determine
A compound of nitrogen and oxygen contains 30.4% nitrogen by mass and has a relative molecular mass of 92. Determine its molecular formula.
Given — Relative atomic masses: N = 14, O = 16.
molecular formula = ............................
(Total for Question 8 = 4 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 — 11 questions, marked on Incandio against the authored scheme, with the mistake you actually made named.
- Teach it — explain Empirical and Molecular Formulae to Ember, an AI pupil who does not have it yet and asks the awkward question.
- Defend it — argue it against Justus von Liebig over three rounds, marked against descriptors you can read first.
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Back to the lesson
- Empirical and Molecular Formulae — Working out a formula you were never told, from nothing but the masses on a balance.
- All of Incandio Chemistry · Incandio Exam Practice