Look inside the OCR GCSE Chemistry A, Foundation tier guide (J248)

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OCR · GCSE · J248
Chemistry A Foundation
Active Recall Guide
1,070 questions
Chemistry A FoundationContents
Contents
6 topics, 72 subtopics
  1. Chemical Reactions193
  2. Elements, Compounds and Mixtures253
  3. Global Challenges306
  4. Monitoring and Controlling Chemical Reactions145
  5. Particles60
  6. Predicting and Identifying Reactions113
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Elements, Compounds and MixturesQuestions
Elements, Compounds and Mixtures
Purity, and melting point data
  1. In science, what does it mean to say that a substance is pure?
  2. What does the word 'pure' usually mean when it is used about food or drink in everyday language?
  3. Why would a carton labelled 'pure orange juice' not count as pure to a chemist?
  4. Is bottled spring water a pure substance in the scientific sense?
  5. Can a mixture of two elements ever be described as pure in the scientific sense?
  6. A sample contains nothing but copper atoms. Is it an element, a compound or a mixture, and is it pure?
  7. Give an example of a substance that is chemically pure but that many people would not call pure in everyday speech.
  8. Why do chemists need a stricter definition of purity than the everyday one?
  9. How does a pure substance behave when it is heated up to its melting point?
12
Elements, Compounds and MixturesAnswers
Answers
Purity, and melting point data
  1. A pure substance is a single element or a single compound, with nothing else mixed into it.
  2. In everyday use it means nothing has been added, so the product is natural or unadulterated.
  3. Because orange juice is a mixture of water, sugars, acids and many other compounds rather than one single compound.
  4. No, because it is a mixture of water with dissolved minerals and gases.
  5. No, because a pure substance contains only one element or only one compound.
  6. It is an element, and it is pure because only one kind of atom is present.
  7. Distilled water containing nothing but H₂O, which some people would describe as processed rather than pure.
  8. Because properties such as melting point and boiling point only take fixed, predictable values when a single element or compound is present.
  9. It melts sharply at one fixed temperature.
13
Global ChallengesQuestions
Global Challenges
The Haber process and fertiliser production
  1. What is the main use of the ammonia made by the Haber process?
  2. Why do crops need nitrogen compounds from fertiliser rather than taking nitrogen from the air?
  3. Explain how making ammonia on a large scale increases food production.
  4. What happens to the nitrogen content of soil that is cropped year after year without fertiliser?
  5. Which two substances are combined in the Haber process, and what is produced?
  6. Before the Haber process, where did farmers get nitrogen compounds for their fields?
  7. Give one environmental problem caused by the heavy use of nitrogen fertilisers.
  8. Why is the Haber process described as important to a growing world population?
  9. How is ammonium sulfate prepared in the laboratory?
34
Global ChallengesAnswers
Answers
The Haber process and fertiliser production
  1. Making nitrogen-containing fertilisers.
  2. Plants cannot use nitrogen gas directly, so they take up soluble nitrogen compounds through their roots.
  3. It supplies cheap nitrogen fertiliser, which raises the crop yield obtained from the same area of land.
  4. It falls, because every harvest removes nitrogen compounds that are not replaced.
  5. Nitrogen and hydrogen combine to produce ammonia.
  6. From manure and from mined natural deposits of nitrates, both of which were limited in supply.
  7. Fertiliser washed into rivers and lakes causes rapid algal growth, which removes oxygen from the water.
  8. It allows enough fertiliser to be made to feed far more people than the same land could otherwise support.
  9. Ammonia solution is titrated with dilute sulfuric acid, and the solution formed is then crystallised.
35
ParticlesQuestions
Particles
The particle model and changes of state
  1. What does the particle model assume about the particles that make up a substance?
  2. Describe the arrangement and movement of the particles in a solid.
  3. Describe the arrangement and movement of the particles in a liquid.
  4. Describe the arrangement and movement of the particles in a gas.
  5. Name the change of state in which a solid becomes a liquid, and the reverse change.
  6. Name the change of state in which a liquid becomes a gas, and the reverse change.
  7. What is the name for a solid changing directly into a gas without becoming a liquid first?
  8. Explain, in terms of particles, why energy must be supplied to melt a solid.
  9. Explain why a gas can be compressed easily but a solid cannot.
56
ParticlesAnswers
Answers
The particle model and changes of state
  1. It assumes that all substances are made of tiny particles that are constantly moving and are attracted to one another.
  2. They are packed closely together in a regular arrangement and vibrate about fixed positions.
  3. They are still close together but arranged randomly, and they move around and slide past one another.
  4. They are far apart and arranged randomly, and they move quickly in all directions.
  5. A solid becoming a liquid is melting, and a liquid becoming a solid is freezing.
  6. A liquid becoming a gas is boiling or evaporating, and a gas becoming a liquid is condensing.
  7. Sublimation.
  8. Energy is needed to make the particles vibrate more strongly and to overcome the forces of attraction holding them in their fixed positions.
  9. In a gas there are large spaces between the particles that can be squeezed out, whereas in a solid the particles are already touching.
57
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1,070
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72 subtopics

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1,070 questions
Across 72 subtopics, every one of them from specification J248.
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Print it, or work from a screen with a notebook beside you.
Answers after, not beside
Covering the answers is a matter of not turning the page, which is what makes the closed-book pass possible.

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.

  1. Step 1 · Closed book

    Cover the answers. Work through one subtopic and write down what you can. Leave blanks where you have nothing.

  2. 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.

  3. 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.

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