1. Water Why is water so important to us? ● We cannot live without water. ● We need water for washing, cleaning, cooking. ● Water carries sewage away from homes. ● Water is often taken for granted in Ireland, but we should not waste water and should always be careful so as not to pollute our valuable water.

2. ● The continuous recirculation of water is called the water cycle. ● The Earth's surfure is covered witth about 80% water. ● We get our water from, rivers, lakes and wells. ● The water is continuously moving from the Earth to clouds and back again ● Without the water cycle life on Earth could not survive ● Don't forget water cycle song Water

4. Water is a very unusual liquid. It has many unique properties. (1) Freezing point of pure water is 0 a C and boiling point 100 a C (2) Water expands when it freezes (What problems do this cause?) (3) The density of water is 1g/cm 3 greater than ice so ice floats. (what is the significance of this? (4) Water is an excellent solvent. (5) Water clings to glass. (How does explain the shape of the meniscus? (6) Tests for water (a) turns blue cobalt chloride paper pink and (b) turns white annhydrous copper sulphate blue. (What does annhydrous mean?) Properties of Water

5. Water Treatment ● In the early days people took their water from the local stream, river or lake. ● As towns and cities grew this led to outbreaks of diseases like cholere, typhoid, and river blindness. ● The diseases came about because the same water was used for washing, drinking, outflow from factories and houses entering the river. ● This is why it is necessary to treat water for drinking.

6. STAGES OF WATER TREATMENT ● Screening ● Settling ● Filtration ● Chlorination ● Fluoridation ● show video clip on water treatment. Water Treatment

7. ● Screening-involves passing the water through wire mesh and removing floating debris such as twigs, plastic bags etc ● Settling – involves the water going into large tanks called sedimentation tanks. Here alum is added to take the cloudiness from the water. (causes coagulation- what is this?). What is the cloudiness due to? ● Filtration – the water is passed though filter beds made of layers of sand and gravel to remove smallest particles of dirt from the water. ● Chlorination – small amounts of chlorine are added to kill bacteria and germs. ● Fluoridation – a fluoride compound is added like sodium fluoride to help prevent tooth decay. Water Treatment

8. Pure Water ● Pure water is water that contains no dissolved or undissolved substances. ● Since water is such a good solvent it rarely found in its pure state ● The purest form of water is distilled water. ● Tap water contains substances like: – Dissolved gases like O 2 and CO 2 – Dissolved solids from flowing over rocks. ● Dissolved substances like calcium compounds are good for us and give the water a more refreshing taste.

9. To Show Water Contains Dissolved Solids ● How might you show that water contains dissolved solids? ● Make a list of the apparatus you might use?

10. Hard and Soft Water ● Water that does not form an immediate lather with soap is called hard water. ● Hardness of water is due to the presence of soluble calcium and magnesium compounds. An example of these compounds are calcium hydrogen carbonate Ca(HCO 3 ) 2, calcium sulphate and magnesium sulphate ● The addition of soap forms an insoluble scum. ● Calcium ions + soap ion → scum ● The action of acidic rainwater on limestone causes hardness in water ● Calcium + Carbon + Water → calcium hydrogen carbonate ● carbonate dioxide (soluble in water)

11. Removal of Hardness from Water ● Hardness in Ireland is mostly caused by soluble calcium hydrogen carbonate in the water. When water is heated or boiled it changes to insoluble calcium carbonate leaving a fur or scale. ● The build up of this fur can eventually block pipes and cause problems in dishwashers, washing machines etc. ● Removal of hardness from water is called water softening. ● All water softening methods involve removal of calcium and magnesium ions from water. There are too methods we need to know ● (a) boiling (b) Ion exchange. ● Boiling removes hardness due to calcium hydrogen carbonate only. The boiling converts it into insolule calcium carbonate.

12. ● Ion exchangers have the ability to swap the ions that cause hardness for ions that don't cause hardness. ● An ion exchange resin swaps calcium and magnesium ions for sodium ions which are soluble in water. (What are ions?) Removal of Hardness from Water

13. ● Deionised water – is water which has all its ions removed. ● Distilled water is pure water everything that is dissolved, gases, ions etc have been removed. ● The advantages and disadvantages are of hard water are:

14. Splitting Water into its Elements ● When electricity is passed through water a chemical reaction takes place. A little H 2 SO 4 is added to help the water conduct electricity. This is done with a Hofmann voltameter shown here. The platinum conected to the positive fo the battery is called the positive electrode. The platinum connected to the negative of the battery is called the negative electrode. Notice twice as much Hydrogen is formed as Oxygen How do you test for hydrogen and oxygen?

15. Electrolysis ● Electrolysis is the cause of a chemical change by electricity. ● In this case: ● water → hydrogen + oxygen ● Michael Faraday a famous British scientist electrolysis to chemistry. Michael Faraday, FRS (22 September 1791 – 25 August 1867) was an English chemist and physicist (or natural philosopher, in the terminology of the time) who contributed to the fields of electromagnetism and electrochemistry.