1. Learning objectives. Explain why clean water is essential Explain how and why water is purified Explain why purification leaves soluble salts in water Give 3 sources of water (not taps!) Give 3 ways that water is used as a resource. Give some reasons why water must be purified before it is used. List some of the pollutants found in tap water. Describe how water can be purified, explain how each stage works and the impurities that are removed at each stage Should all dissolved substances be removed from water? http://www.y outube.com/ watch?v=9z 14l51ISwg

2. a)The removal of large insoluble materials is …….. b)Adding chemicals to make particles stick together and sink is …….. c)Adding a toxic gas to destroy microbes is ………..

3. Water used to dissolve other chemicals Water used to cool power stations  Water used to make other chemicals raw material solvent coolant

4. Add sodium hydroxide solution and aluminium powder to the solution containing the nitrate ions. The aluminium reduces the nitrate ion (NO3-) to an ammonium ion (NH4+). The ammonium ion reacts with hydroxide to produce ammonia gas and water. ammonium + hydroxide ammonia + water NH4+(aq) + OH-(aq) NH3(g) + H2O(l) Ammonia gas can be identified using damp red litmus paper. http://www.absorblearning.com/media/item.action?quick=v7 Testing for the presence of NITRATE ( NO3-) ions.

5. Testing for the presence of impurities in water. Water supplies are often contaminated with impurities. Insoluble substances can be filtered out of the water but soluble substances such as minerals are harder to remove. Tests can be carried out to determine the presence of the soluble contaminants. Precipitation reactions can be used to identify the contaminants.

6. 1.To identify the presence of HALIDE ions; You will need test tubes containing sodium chloride solutionCl - sodium bromide solution Br - sodium iodide solutionI - Add a few drops of silver nitrate solution. Record the colour of the precipitate formed. 2.To identify the presence of Lead Pb 2+ ions; You will need a test tube containing lead nitrate solution Add a few drops of potassium iodide solution. Record the colour of the precipitate formed. 3.To identify the presence of Sulphate SO 4 2- ions; You will need a test tube containing sodium sulphate solution Add a few drops of barium chloride solution. Record the colour of the precipitate formed.