OCR GCSE Chemistry A, Higher tier sample questions and answers (J248)
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30 sample questions and answers
Taken from every topic of OCR GCSE Chemistry A, Higher tier, specification J248. The full guide has 1,265.
Paper 3
Chemical Reactions
276 questions in the guide, across 17 subtopics. More from this topic
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Writing formulae of elements and compounds
Sodium chloride is written NaCl even though it has no molecules. What does this formula represent?
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The simplest whole-number ratio of the ions in the giant lattice, one sodium ion to one chloride ion. -
Ionic equations, and state symbols
Write the ionic equation for magnesium reacting with a dilute acid.
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Mg(s) + 2H⁺(aq) → Mg²⁺(aq) + H₂(g). -
Conservation of mass, and changes of mass in open systems
4 g of hydrogen reacts completely with 32 g of oxygen. What mass of water is formed?
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36 g. -
Exothermic and endothermic reactions, and reaction profiles
Why is an instant cold pack for a sports injury based on an endothermic change?
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It takes in energy from its surroundings, so it cools the injury. -
Oxidation and reduction, by oxygen and by electrons
In Fe₂O₃ + 3CO → 2Fe + 3CO₂, name the reducing agent and explain your choice.
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Carbon monoxide, because it removes oxygen from the iron oxide and is itself oxidised to carbon dioxide.
Paper 3
Elements, Compounds and Mixtures
253 questions in the guide, across 17 subtopics. More from this topic
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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?
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It is an element, and it is pure because only one kind of atom is present. -
Formulations, and separating mixtures
Why do the proportions of the components in a formulation matter so much?
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Because the properties of the finished product depend on the proportions, so changing them gives a product that behaves differently. -
Interpreting chromatograms and Rf values
A substance has an Rf value of 0.60 and the solvent front moved 10.0 cm. How far did the spot move?
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It moved 6.0 cm, because 0.60 × 10.0 = 6.0. -
Metals and non-metals in the Periodic Table
How does a non-metal oxide behave when it dissolves in water?
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It is acidic and gives a solution with a pH below 7. -
Ionic, covalent and metallic bonding compared
Which types of substance contain covalent bonds?
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Simple molecular substances, giant covalent structures and polymers all contain covalent bonds.
Paper 4
Global Challenges
353 questions in the guide, across 22 subtopics. More from this topic
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Extracting metals by reduction and by electrolysis
Give a word equation for the reduction of iron(III) oxide by carbon.
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Iron(III) oxide + carbon → iron + carbon dioxide. -
Rate against yield in industry, and reaction conditions
Where does the hydrogen used in the Haber process come from?
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Mainly from natural gas, by reacting methane with steam. -
Life cycle assessment
A plastic bag is buried in landfill and does not break down. Which stage of a life cycle assessment does this belong to?
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Disposal at the end of the product's life. -
Alloys, and the corrosion of metals
Name three ways of forming a physical barrier on iron to prevent rusting.
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Painting it, coating it with oil or grease, and covering it with plastic or another metal. -
Predicting the products of organic reactions
Which product is formed when hydrogen adds across the double bond of propene?
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Propane, C₃H₈.
Paper 4
Monitoring and Controlling Chemical Reactions
202 questions in the guide, across 12 subtopics. More from this topic
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Concentration in mol/dm³, and titration
Calculate the mass of sodium hydroxide, relative formula mass 40, in 100 cm³ of a solution of concentration 2.00 mol/dm³.
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2.00 × 0.100 = 0.200 mol, and 0.200 × 40 = 8.00 g, given to 3 significant figures. -
Titration calculations, and the mass of a solute
Calculate the mass of potassium hydroxide, relative formula mass 56, in 50.0 cm³ of solution of concentration 0.100 mol/dm³.
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0.100 × 0.0500 = 0.00500 mol, and 0.00500 × 56 = 0.280 g, given to 3 significant figures. -
Theoretical mass and percentage yield
How is the percentage yield of a reaction calculated?
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Divide the actual mass of product obtained by the theoretical mass and multiply by 100. -
Atom economy, and choosing a reaction pathway
Give two reasons why a route with a lower percentage yield might still be chosen over one with a higher yield.
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It may run much faster or at milder conditions and so cost less energy, or its by-products may be saleable while the other route's are not. -
Factors affecting rate, and collision theory
Which of the factors that change rate applies only to reactions involving gases?
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Pressure, because only gases are compressed enough for pressure to change how closely the particles are packed.
Paper 3
Particles
68 questions in the guide, across 5 subtopics. More from this topic
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The particle model and changes of state
Name the change of state in which a liquid becomes a gas, and the reverse change.
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A liquid becoming a gas is boiling or evaporating, and a gas becoming a liquid is condensing. -
The particle model and changes of state
Explain why burning magnesium in air is a chemical change.
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The magnesium atoms join with oxygen atoms to form a new substance, magnesium oxide, which has different properties from the magnesium. -
Limitations of the particle model
Explain why leaving out the forces between particles makes the model poor at explaining boiling points.
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Boiling requires enough energy to overcome the attraction between the particles, so a model with no forces cannot explain why different substances boil at different temperatures. -
Limitations of the particle model
Explain why real particles cannot be solid spheres.
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An atom is mostly empty space, with a tiny nucleus and electrons in the space around it, so it is not solid throughout. -
How the atomic model changed, and the structure of the atom
Explain how Rutherford interpreted the results of the alpha scattering experiment.
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He concluded that an atom is mostly empty space with its positive charge and nearly all its mass concentrated in a tiny nucleus at the centre.
Paper 4
Predicting and Identifying Reactions
113 questions in the guide, across 9 subtopics. More from this topic
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Groups 1, 7 and 0, and why they behave as they do
In what form do the elements of Group 7 exist?
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As diatomic molecules of two atoms sharing a pair of electrons, such as Cl₂ and Br₂. -
Transition metals
What colours are solutions containing copper(II) ions, iron(II) ions and iron(III) ions?
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Copper(II) solutions are blue, iron(II) solutions are pale green and iron(III) solutions are orange-brown. -
Predicting reactivity from the Periodic Table
Predict the formula of the compound formed between potassium and iodine.
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KI, because potassium loses one electron and iodine gains one. -
Reactivity of metals with water and acids
Compare how magnesium reacts with cold water and with steam.
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It reacts extremely slowly with cold water, but burns vigorously in steam to form magnesium oxide and hydrogen. -
Tests for oxygen, hydrogen, carbon dioxide and chlorine
Describe the test for chlorine and its positive result.
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Hold damp blue litmus paper in the gas; chlorine turns it red and then bleaches it white.
OCR GCSE Chemistry A, Higher tier Active Recall Guide
The other 1,235 questions, with the answers printed after each section.