at specific temperatures. Melting point and boiling point data can be used to distinguish pure substances from mixtures. In everyday language, a pure substance can mean a substance that has had nothing added to it, so it is unadulterated and in its natural state, eg pure milk. melting point boiling point. Use data to identify pure and impure substances. Identify the contents of mineral waters sold as ‘pure’. Discuss the meaning of ‘pure’. 4.8.1.2 A formulation is a mixture that has been designed as a useful product. Many products are complex mixtures in which each chemical has a particular purpose. Formulations are made by mixing the components in carefully measured quantities to ensure that the product has the required properties. Formulations include fuels, cleaning agents, paints, medicines, alloys, fertilisers and foods. Identify formulations given appropriate information. Students do not need to know the names of components in proprietary products. WS 1.4, 2.2 0.5 Define the terms: mixture formulation. Research the composition of the following formulations: fuel cleaning agents paints medicines alloys fertilisers foods. Identify the purpose of each chemical in the formulation. 4.8.1.3 Chromatography can be used to separate mixtures and can give information to help identify substances. Chromatography involves a Explain how paper chromatography separates mixtures. 2 Describe a method for paper chromatography. Explain what happens to substances during the Required practical 6: Investigate how chromatography can be used to separate and tell Video clips YouTube: YouTube:
opportunities and resources Reference to past questions that indicate success 4.8.3.1 Flame tests can be used to identify some metal ions (cations). Lithium, sodium, potassium, calcium and copper compounds produce distinctive colours in flame tests: lithium compounds result in a crimson flame sodium compounds result in a yellow flame potassium compounds result in a flame calcium compounds result in an orange-red copper compounds result in a green flame. If a sample containing a mixture of ions is used, some flame colours can be masked. Identify species from the results of the tests in 8.3a to 8.3e. colours of other metal ions are not required knowledge. WS 2.2 1 Describe the flame tests for identifying cations to another student. Research how firework manufacturers produce the different colours in fireworks. Carry out flame tests on the following cations: lithium sodium potassium calcium copper. AT 8 Video clip YouTube: 4.8.3.2 Sodium hydroxide solution can be used to identify some metal ions (cations). Solutions of aluminium, calcium and magnesium ions form white precipitates when sodium hydroxide solution is added but only the aluminium hydroxide precipitate Be able to write balanced equations for the reactions to produce the insoluble hydroxides. Students are not expected to write equations for the 2 Describe how sodium hydroxide can be used to identify some cations to another student. Use sodium hydroxide to test for the following cations: aluminium calcium magnesium copper(ll) iron(ll) iron(lll). AT8
dissolves in excess sodium hydroxide solution. Solutions of copper(II), iron(II) and iron(III) ions form coloured precipitates when sodium hydroxide solution is added. Copper(II) forms a blue precipitate, iron(II) a green precipitate and iron(III) a brown precipitate. production of sodium aluminate. WS 2.2 4.8.3.3 Carbonates react with dilute acids to form carbon dioxide gas. Carbon dioxide can be identified with limewater. 1 Describe how dilute acids can be used to identify carbonates to another student. Use dilute acid to test for the following carbonates: sodium carbonate potassium carbonate. Analyse the composition of an egg shell, testing for the presence of various ions using acids and other test tube reactions and flame tests. Video clip: YouTube: 4.8.3.4 Halide ions in solution produce precipitates with silver nitrate solution in the presence of dilute nitric acid. Silver chloride is white, silver bromide is cream and silver iodide is yellow. 1 Describe how silver nitrate can be used to identify halides to another student. Use silver nitrate to test the following halides: chloride bromide iodide. Video clip: YouTube: 4.8.3.5 Sulfate ions in solution produce a white precipitate with barium chloride solution in the presence of dilute hydrochloric acid. WS 2.4, 2.6 2 Describe how barium chloride in the presence of dilute hydrochloric acid can be used to identify sulfate ions to another student. Plan an analysis programme to identify an Use barium chloride in the presence of dilute hydrochloric acid to test for sulfate ions. Required practical 7: Video clip: