Learning Objectives Key Words – Cobalt paper Filtration Chlorination To describe chemical tests for water To outline the treatment of the water supply in terms of filtration and chlorination Testing for and cleaning water Key Words – Cobalt paper Filtration Chlorination Pollutant Do you know? Some of the uses of water in industry and in the home? 5 Minute Task

The raft of the Medusa was stuck at sea for 2 weeks The raft of the Medusa was stuck at sea for 2 weeks. Why is this such a drastic scene? There seems to be plenty of water around? Transition filler

Key Reactions of Water In your book, write the equation for CuSO4 and CoCl2 combining with water How is this a test for water? Name 4 uses of water

Water purifying Design a water purifying system with the equipment in the room. You have 10 minutes to design and build your device Then we test them with dirty muddy water What other steps are needed to make this drinkable? Draw, label and explain your design

Purifying Water – How we make water safe to drink Starter (5mins) http://www.youtube.com/watch?v=U_atn_3dack State 3 things that are likely to be wrong with this water Suggest how you could remedy each of these problems a) Water of the correct quality is essential for life. For humans, drinking water should have sufficiently low levels of dissolved salts and microbes. b) Water filters containing carbon, silver and ion exchange resins can remove some dissolved substances from tap water to improve the taste and quality. c) Chlorine may be added to drinking water to reduce microbes and fluoride may be added to improve dental health. d) Pure water can be produced by distillation.

Learning Objective Learning Outcomes How water is made safe to drink I can recall that drinking water needs to be clean, odourless, tasteless and free from microbes to avoid disease I can describe the process of water purification as coagulation, sedimentation, filtration, disinfection and fluoridation I can explain why purification by distillation as a main source of potable water is restricted to wealthy countries I can explain what happens at each stage of the normal purification process of water I can present an argument for the continued fluoridation of water

Instructions for Market Place Activity Split into small groups. Each group is provided detailed information regarding 1 aspect of how water is made safe to drink You have 10mins to make a poster/diagram conveying as much information on your sheet as possible You can not use more than 15 words (excluding the title), but you can use as many chemical symbols and numbers as you like task 2 (10mins)

Gathering your information task 3 (8mins) You have 2mins per poster to capture as much information as possible Overview You have 5mins to make a poster/diagram conveying as much information on water filtration as possible You can not use more than but you can use as many chemical symbols and numbers as you like

The floc settles to the bottom of the tank under gravity. Coagulation The coagulant Aluminium Sulphate is added This causes impurities to clump or coagulate together Impurities sink to the bottom as “floc” Adding Aluminium Sulphate (Alum) causes clay, dirt and other organic matter to clump together to form large particles of floc. The floc settles to the bottom of the tank under gravity. This helps the subsequent removal of particles by sedimentation and filtration.

Sedimentation The large tanks allow the floc to settle to the bottom as sludge under gravity. The water spends a total of about 5 hours in the tank. The flow is continuous. The dripping of the water into the tank allows extra oxygen to mix with the water. This provides more oxygen for microbial respiration in bacteria which are responsible for decomposing organic matter that enters the sedimentation tank.

Relatively clean water leaves the filtration bed This is the final step in removing suspended particles and any unsettled floc Water moves through a layer of charcoal or coal before being further filtered by the sand. This acts as an excellent microfilter, trapping air which again increases available oxygen for microbial respiration, thus helping decomposition Most particles pass through surface layers but are trapped in pore spaces or stick to sand particles. Relatively clean water leaves the filtration bed

Disinfection and Fluoridation The disinfection of water by adding chlorine gas is called chlorination. Chlorine was used for the first time in 1850 when John Snow used it in London’s water system to combat cholera. This has resulted in a significant decrease in the number of deaths caused by cholera, typhoid, diarrhoea and hepatitis A. Today, chlorination is used to treat most of drinking in the world since it is easy, inexpensive and reliable. Fluorine is also added to water to strengthen teeth. This prevents tooth decay. Some people are against the fluoridation of because they believe it could be linked to cancer and tooth flecking. Scientists are divided as there seems to be insufficient evidence and no difference in levels of cancer in fluoridated and unfluoridated areas

Questions of water safety State 3 things that make water unfit to drink List the stages involved in water purification Why is chlorine added to water? Why is fluorine added to water? Why do some people campaign against the fluoridation of water? What is sedimentation and why is it useful? How does aluminium sulphate help sedimentation Why is unclean water dripped slowly over large filter beds at sanitation plants plenary (4min) C3.2.2 Purifying water a) Water of the correct quality is essential for life. For humans, drinking water should have sufficiently low levels of dissolved salts and microbes. b) Water filters containing carbon, silver and ion exchange resins can remove some dissolved substances from tap water to improve the taste and quality. c) Chlorine may be added to drinking water to reduce microbes and fluoride may be added to improve dental health. d) Pure water can be produced by distillation. Suggested ideas for practical work to develop skills and understanding include the following: ■ investigation of which ions cause hard water, eg adding soap solution to solutions of NaCl, CaCl2, KCl, and MgCl2 ■ making temporary hard water by adding excess carbon dioxide to limewater ■ determining hardness of samples of water – shake with soap solution – measuring cm3 of soap to get permanent lather ■ the removal of hardness: – temporary hardness: test before and after boiling, with soap – permanent hardness: test before and after addition of sodium carbonate ■ testing hard water before and after passing through an ion exchange column ■ using conductivity sensors to analyse different samples of hard and soft water ■ design and carry out an investigation to compare the effectiveness of commercial water softeners using soap titration ■ investigating the various types of water ‘filters’ that are commercially available ■ distillation of seawater – design a simple apparatus to do the distillation and check the quality of the distillate (boiling point and evaporation to dryness of a sample on a watch glass).

Water Purification What percentage of the Earth’s water is drinkable What percentage of the Earth’s drinkable water is locked in Icecaps and glaciers What percentage of this is accessible(surface water)? What percentage of the Earth’s fresh water is found in lakes And what percentage is found in rivers? Much of the drinking water in Saudi Arabia is obtained by distillation of sea water. Explain why this is not an option for a country like Zimbabwe Suggest a reason why each of the following might be found in drinking water: Nitrates, Lead and Pesticides To be done by students waiting for others to finish Why don’t we just evaporate sea water on an industrial scale to make fresh drinkable water?

Homework Find out how water filters containing carbon and silver ions are used as exchange resins to remove dissolved particles to improve the taste of water