OCR GCSE Combined Science Chemistry, Foundation tier Active Recall Guide (J250)
OCR · GCSE
OCR GCSE Combined Science Chemistry, Foundation tier Active Recall Guide
Every topic of specification J250 written as exam-style questions with the answers printed after them. 797 questions across 6 topics and 53 subtopics, at Foundation tier, covering Paper 3 (Chemistry) and Paper 4 (Chemistry).
- OCR
- GCSE
- Specification J250
- 797 questions
Guide overview All topics Sample questions Papers and weighting Look inside Questions and answers
What the exam asks of you
OCR GCSE Combined Science A (Gateway Science, specification J250) is worth two GCSEs and is examined by six papers, two for each science, each 1 hour 10 minutes and 60 marks. The chemistry content is sat as Paper 3 (Chemistry) and Paper 4 (Chemistry), together a third of the qualification. This is the Foundation tier, which sits its own pair of papers and offers grades 5–5 to 1–1 of the double award.
Combined Science covers three sciences in the time most schools give to two, which makes it the qualification where forgetting costs the most. Working one subtopic at a time is what keeps the chemistry third from slipping while the other two are being taught.
| Paper | Covers | Length | Marks | Weighting |
|---|---|---|---|---|
|
Paper 3 (Chemistry) Paper 3 (Chemistry) |
Chemical Reactions Elements, Compounds and Mixtures Particles Tests for oxygen, hydrogen, carbon dioxide and chlorine, from Predicting and Identifying Reactions |
1 hour 10 minutes | 60 marks | 16.7% |
|
Paper 4 (Chemistry) Paper 4 (Chemistry) |
Global Challenges Monitoring and Controlling Chemical Reactions Predicting and Identifying Reactions, apart from the gas tests |
1 hour 10 minutes | 60 marks | 16.7% |
What is in the guide
All topics
Every topic has its own page with its subtopics, what it covers and sample questions.
Sample questions
Taken from the guide. Answer each one closed book first, then open the answer.
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Writing formulae of elements and compounds
What is the formula of carbon dioxide, and what does the subscript tell you?
Show the answer
CO₂, where the subscript 2 shows that each molecule contains two oxygen atoms. -
Purity, and melting point data
A sample contains nothing but copper atoms. Is it an element, a compound or a mixture, and is it pure?
Show the answer
It is an element, and it is pure because only one kind of atom is present. -
Extracting metals by reduction and by electrolysis
Give a word equation for the reduction of iron(III) oxide by carbon.
Show the answer
Iron(III) oxide + carbon → iron + carbon dioxide. -
Measuring the rate of a reaction, and rate graphs
Give the units in which a rate of reaction is expressed when gas volume is measured, and when mass loss is measured.
Show the answer
Gas volume gives a rate in cm³/s or cm³/min, and mass loss gives a rate in g/s or g/min. -
The particle model and changes of state
Name the change of state in which a liquid becomes a gas, and the reverse change.
Show the answer
A liquid becoming a gas is boiling or evaporating, and a gas becoming a liquid is condensing. -
Groups 1, 7 and 0, and why they behave as they do
In what form do the elements of Group 7 exist?
Show the answer
As diatomic molecules of two atoms sharing a pair of electrons, such as Cl₂ and Br₂.
How the guide is worked
Answering a question from memory stores it far better than reading the answer again. The guide runs that as a fixed procedure on one subtopic at a time, about twenty minutes a session.
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Step 1 · Closed book
Cover the answers. Work through one subtopic and write down what you can. Leave blanks where you have nothing.
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Step 2 · Open book
Go back to the top. Read each printed answer and write it out in full, including the ones you had right.
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Step 3 · Closed book again
Same questions, same order, from memory. The gap between pass one and pass three is the session result.
Read the full method, the return schedule and the research behind it.
Look inside
Questions for a subtopic print together and the answers for that section print after them.
- Chemical Reactions193
- Elements, Compounds and Mixtures221
- Global Challenges165
- Monitoring and Controlling Chemical Reactions105
- Particles60
- Predicting and Identifying Reactions53
- In science, what does it mean to say that a substance is pure?
- What does the word 'pure' usually mean when it is used about food or drink in everyday language?
- Why would a carton labelled 'pure orange juice' not count as pure to a chemist?
- Is bottled spring water a pure substance in the scientific sense?
- Can a mixture of two elements ever be described as pure in the scientific sense?
- A sample contains nothing but copper atoms. Is it an element, a compound or a mixture, and is it pure?
- Give an example of a substance that is chemically pure but that many people would not call pure in everyday speech.
- Why do chemists need a stricter definition of purity than the everyday one?
- How does a pure substance behave when it is heated up to its melting point?
- A pure substance is a single element or a single compound, with nothing else mixed into it.
- In everyday use it means nothing has been added, so the product is natural or unadulterated.
- Because orange juice is a mixture of water, sugars, acids and many other compounds rather than one single compound.
- No, because it is a mixture of water with dissolved minerals and gases.
- No, because a pure substance contains only one element or only one compound.
- It is an element, and it is pure because only one kind of atom is present.
- Distilled water containing nothing but H₂O, which some people would describe as processed rather than pure.
- Because properties such as melting point and boiling point only take fixed, predictable values when a single element or compound is present.
- It melts sharply at one fixed temperature.
questions
Scroll sideways to turn through the pages.
Questions students ask first
Gateway or Twenty First Century? Which am I on?
OCR runs two GCSE science suites. Gateway Science is Combined Science A, J250, which is this guide. Twenty First Century Science is Combined Science B, J260 and is organised completely differently.
The code is on your exam timetable. Gateway chemistry topics are numbered C1 to C6.
Higher or Foundation. Which do I need?
This is the Foundation tier guide, offering grades 5-5 to 1-1 of the double award.
At OCR the tier also changes the paper number. Foundation sits Papers 1 to 6 and Higher sits Papers 7 to 12. You are sitting Paper 3 (Chemistry) and Paper 4 (Chemistry).
Your teacher decides the entry, usually during Year 11. If you are moved up to Higher you will need the Higher guide, which adds the higher-tier content.
I do the separate sciences, not Combined Science.
Then you need a different guide. The separate sciences are Chemistry A (J248) and they examine more chemistry than Combined Science does.
The one you want is OCR GCSE Chemistry A, Foundation.
Which topics are on which paper?
Paper 3 (Chemistry) covers Chemical Reactions, Elements, Compounds and Mixtures, Particles, Tests for oxygen, hydrogen, carbon dioxide and chlorine, from Predicting and Identifying Reactions. Paper 4 (Chemistry) covers Global Challenges, Monitoring and Controlling Chemical Reactions, Predicting and Identifying Reactions, apart from the gas tests.
The second paper assumes the content of the first, so nothing from the first half is ever safely dropped. The full breakdown is here.
OCR GCSE Combined Science Chemistry, Foundation tier Active Recall Guide
Every question paired with its answer, grouped by topic and subtopic, ready to work in three passes.