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Water

Water. CHEMISTRY 2. Additional Science. Chapter 8. The Importance of Water. Water is used widely as a coolant in industrial processes. Water is essential to life on Earth. Additional Science. 75% of the world’s surface is covered by water.

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Water

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  1. Water CHEMISTRY 2 Additional Science Chapter 8

  2. The Importance of Water Water is used widely as a coolant in industrial processes Water is essential to life on Earth Additional Science 75% of the world’s surface is covered by water Water is used widely as a solvent in industrial processes Chapter 8

  3. Solids allowed to settle Chlorination to kill bacteria Filtration to remove smaller particles Storage in tank or water tower before use by schools. Factories etc. The public water supply Cl 35 17 Additional Science Water from river, lake or underground well stored in a reservoir Chapter 8 • This is the process that takes place to ensure that we have a supply of drinking water. Some water authorities add other chemicals to drinking water e.g. many add fluoride ions which prevent tooth decay at controlled levels.

  4. This fact can be used to prove for water hardness, and to compare the hardness of different samples. Hard water As rain water flows through rocks, it picks up calcium and magnesium ions. The result is - hard water. Hard water forms scale (calcium carbonate) in pipes, and restricts water flow. Hard water mixes with soap to form calcium or magnesium stearate which is insoluble – this is why soap scum forms. Hard water doesn’t produce soap suds easily. Additional Science Chapter 8

  5. Temporary hardness Permanent hardness Reason:- Presence of calcium or magnesium sulphate in the water. Reason:- Presence of calcium or magnesium carbonate in the water Solution:- Soften the water by adding sodium carbonate or by ion exchange. Solution:- Boiling the water. The hydrocarbonates decompose, leaving insoluble calcium carbonate or magnesium carbonate – this is the scale found in kettles and boilers. Equation:- Na2CO3 + CaSO4 Ca CO3 + Na2SO4 Equation:- Ca(HCO3)2 Ca CO3 + CO2 + H2O Types of hardness Additional Science Chapter 8

  6. It produces boiler scale Hard water tastes better than soft water. Beer production often involves artificially hardening the water. Uses more energy to boil the water Reduces the efficiency of kettles, boilers, coffee machines etc. More soap has to be used, resulting in soap scum in the wash. Modern detergents are used instead of soap in washing machines. Removing boiler scale is expensive Disadvantages Advantages Hard water Additional Science Chapter 8

  7. Solubility curves Terms Solute – the substance that dissolves (sugar). Solvent– the liquid doing the dissolving (water). Solubility – mass of solute that dissolves in a certain mass of solvent. water sugar The sugar doesn’t dissolve in the water any longer – you have a saturated solution. Usually the solubility of a solute increases with an increase in temperature Additional Science Solubility curve Chapter 8 sodium chloride Can you think which solute’s solubility is most affected? Solubility/ g per 100g of water potassium chlorate Temperature °C

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