Edexcel GCSE Chemistry Topic 5: Separate Chemistry 1 Exam Questions

About Edexcel GCSE Chemistry Topic 5: Separate Chemistry 1

Topic 5 of Edexcel GCSE Chemistry contains content studied only by separate Chemistry students and is assessed on Paper 1. It extends earlier topics in several directions: the properties of transition metals, corrosion and its prevention, alloys, percentage yield and atom economy, concentration in mol dm-3 with acid-alkali titrations (a core practical), molar gas volume at Higher tier, the production of fertilisers and conditions in the Haber process, and chemical cells and hydrogen fuel cells. Because it draws on Topics 1, 3 and 4, examiners often set multi-step questions combining calculation, practical method and evaluation of industrial choices.

What you need to know

• Transition metals Transition metals have high melting points and high densities, form coloured compounds and, with their compounds, act as catalysts, for example iron in the Haber process.
• Corrosion and alloys Rusting of iron needs oxygen and water. It is prevented by excluding oxygen and water (painting, oiling, plastic coating), by sacrificial protection with a more reactive metal such as zinc (galvanising), or by electroplating. Alloys are harder than pure metals because different-sized atoms disrupt the layers; examples include steel, brass and magnalium.
• Yield and atom economy Percentage yield = actual yield / theoretical yield x 100. Atom economy = relative formula mass of desired product / sum of relative formula masses of all reactants x 100. A high atom economy means less waste.
• Concentration and titrations Concentration can be in g dm-3 or mol dm-3. Core practical: carry out an accurate acid-alkali titration using a burette, pipette and indicator. Higher tier only: calculate unknown concentrations from titration results.
• Molar gas volume (Higher tier only) One mole of any gas occupies 24 dm3 at room temperature and pressure. Use this to calculate volumes of gaseous reactants and products from equations.
• Haber process and fertilisers The Haber process makes ammonia at about 450 °C, 200 atmospheres and with an iron catalyst; conditions are a compromise between rate, yield and cost. Ammonia is used to make fertilisers such as ammonium nitrate and ammonium sulfate. Ammonium sulfate is made in the laboratory by titration and crystallisation, and in industry by a continuous multi-stage process.
• Chemical and fuel cells Chemical cells produce a voltage until a reactant is used up. A hydrogen-oxygen fuel cell produces a voltage continuously while fuel and oxygen are supplied; the only product is water. Fuel cells are compared with rechargeable batteries in terms of cost, storage and pollution.

Common mistakes in Topic 5: Separate Chemistry 1

• Giving 'high melting point and conductor' as transition metal properties that distinguish them from all metals. Learn the specific ones: high density, coloured compounds and catalytic activity.
• Saying a zinc coating protects iron only as a barrier. Zinc is more reactive, so it corrodes preferentially (sacrificial protection).
• Confusing percentage yield and atom economy. Yield uses masses actually obtained; atom economy uses relative formula masses from the equation.
• Forgetting to divide cm3 by 1000 when calculating moles or concentration.
• Using 24 dm3 for solids or liquids. Molar gas volume applies only to gases.

Try three Topic 5: Separate Chemistry 1 exam-style questions