Pure elements and compounds melt and boil 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. Recall melting and boiling points. Identify the contents of mineral waters sold as pure water. Draw diagrams to illustrate pure distilled with bottled water. determine which one is not pure water. 5.8.1.2 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, Identify formulations given appropriate information. Students do not need to know the names of components in proprietary products. WS 1.4, 2.2 1 Define the terms: • mixture • formulation. out one or more of the applied chemistry experiments. Produce a display that describes the composition of the one of the following formulations: • fuel • cleaning agents • paints • medicines • alloys Making soap: Making glue: Making cut flower preservative: Comparing detergents: Producing a foam: Making milk of Magnesia: Investigating pigments: Making fertiliser:
medicines, alloys, fertilisers and foods. • fertilisers • foods. Identify the purpose of the chemicals in the chosen formulation and with class. Making an alloy: 5.8.1.3 Chromatography can be used to separate mixtures and can give information to help identify substances. Chromatography involves a stationary phase and a mobile phase. Separation depends on the distribution of substances between the phases. The ratio of the distance moved by a compound (centre of spot from origin) to the distance moved by the solvent can be expressed as its Rf value: Different compounds have different Rf values in different solvents, can be used to help identify the Explain how chromatography separates mixtures. Suggest how chromatographic methods can be used for distinguishing pure substances from impure substances. Interpret chromatograms and determine Rf values from chromatograms. Provide answers to an appropriate number of significant figures. WS 2.4, 2.6 MS 1a, 1c, 1d, 2a 2 Describe a method for chromatography. Describe what happens to substances during the process of chromatography. Describe what the Rf value is and write instructions on how to calculate the Rf value. Use chromatograms to work out Rf values. Describe how chromatographic methods could be used to find out whether a substance was pure or not. Required practical 12: Investigate how paper chromatography can be used to separate and tell the difference between coloured substances. Students should calculate Rf values. AT skills covered by this practical activity: 1 and 4. Video clips YouTube: YouTube:
compounds. The compounds in a mixture may separate into different spots depending on the solvent but a pure compound will produce a single spot in all solvents. 5.8.2 Identification of common gases Spec ref. Summary of the specification content Learning outcomes What most candidates should be able to do Suggested timing (hours) Opportunities to develop scientific communication skills Opportunities to develop and apply practical and enquiry skills Self/peer assessment Opportunities and resources Reference to past questions that indicate success 5.8.2.1 The test for hydrogen uses a burning splint held at the open end of a test tube of the gas. Hydrogen burns rapidly with a pop sound. 0.5 Describe the test for hydrogen. Demonstrate the combustion of hydrogen: Carry out a simple test for hydrogen: Video clip YouTube: 5.8.2.2 The test for oxygen uses a glowing splint inserted into a test tube of the gas. The splint relights in oxygen. 0.5 Describe the test for oxygen. Demonstrate that contains dissolved oxygen so fish can breathe: