GCSE Chemistry Practicals: Making Salts and Purifying Water

Two of the practicals in GCSE Chemistry are about making something pure: a dry, crystalline sample of a soluble salt, and clean water from a salty or dirty sample. Exam questions on them rarely ask for a single fact. They ask you to put steps in order, explain why each step is there, predict what is left on the filter paper, decide how you know a reaction has finished, or turn a set of masses into a concentration. This material practises exactly that, and complements the category's acids, bases and salts material (which covers the chemistry of salts) and its using resources material (which covers how drinking water is produced on a large scale).

The quiz follows the preparation of copper(II) sulfate crystals from copper(II) oxide and dilute sulfuric acid from start to finish: recognising when enough oxide has been added, choosing the correct order of steps, naming the residue left after filtering, explaining why the solution is heated over a water bath and what goes wrong if it is heated to dryness, and recognising the end of the reaction when a carbonate is used instead of an oxide. A safety question asks for the right precaution when warming acid.

The water questions cover the analysis and purification of water samples: why a pH meter gives a more precise reading than universal indicator, how to calculate the concentration of dissolved solids from the masses of an evaporating basin before and after evaporation, why cooling water enters a condenser at the bottom, and how to show that the distillate is pure water.

The flashcards give each step with its reason, the definitions of residue and filtrate, and the formula for dissolved solids. In the oral exam an examiner asks you to talk through a method, one question at a time, and gives brief, precise feedback at the end — a good rehearsal for the six-mark method questions. The printable written work contains eight longer tasks answered by hand: a full method for copper(II) sulfate crystals with reasons, a salt made from a carbonate, interpreting observations, a risk assessment, planning the analysis of three water samples, a dissolved-solids calculation, a distillation method with a purity test, and a percentage yield of crystals at Higher tier. Each task is checked against a model answer.

The content is based on the practical skills and the required practical activities in the DfE GCSE chemistry subject content; the two practicals correspond, for example, to AQA's required practicals on preparing a pure, dry sample of a soluble salt and on the analysis and purification of water samples.

• Describe, in order, how to make pure, dry crystals of a soluble salt from an insoluble oxide or carbonate
• Explain the reason for each step: warming, adding excess, filtering, concentrating and crystallising
• Identify the residue and the filtrate and describe the observations at each stage
• Choose suitable safety precautions for heating acids and solutions
• Measure the pH of water samples and compare a pH meter with universal indicator
• Calculate the concentration of dissolved solids from mass measurements
• Describe how to distil a water sample and show that the distillate is pure water

Practice material written by Zestly, based on the DfE GCSE chemistry subject content (working scientifically and the required practical activities on making salts and on the analysis and purification of water samples); practical names follow, as an example, the AQA GCSE Chemistry (8462) specification. All data in the questions are illustrative.