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C 3 Chemicals in Our Lives – Risks & Benefits. Lesson 3: Salt. Objectives. MUST remember that salt has many uses SHOULD understand that salt can be obtained from sea water or from underground rocks
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C3 Chemicals in Our Lives – Risks & Benefits Lesson 3: Salt
Objectives • MUSTremember that salt has many uses • SHOULD understand that salt can be obtained from sea water or from underground rocks • COULD explain how salt is extracted from underground deposits and the effect this has on the environment
KeyWords • You need to be able to define the following: • Sediment • Sedimentary rock • Eroded • Dissolved • Evaporated
Textbook Answers 1) Flavouring; as a preservative. 2) By evaporating water from sea water. 3) To lower the freezing point of ‘water’ so that ice does not form. 4)Mining – rock salt is dug out and carried to the surface; solution mining – water is pumped into the salt deposits and brine is pumped out.
Textbook Answers 5) To prevent subsidence; the remaining salt holds the roof of the mine up. 6)For – salt is needed for many purposes; employment. Against – loss of habitats/high salt concentration kills wildlife; increased transport; possible contamination of water supplies.
Worksheet Answers Activity 1 (Low demand) 1) [1] Sea water is run into artificial ponds. [2] The Sun evaporates some of the water off. [3] The salt water is run from one pond to another becoming more concentrated. [4] More water evaporates and solid salt begins to form on the bottom of the pond. [5] The remaining sea water is let out of the pond. [6] The solid salt is shovelled into heaps to dry out. 2) Treating roads in winter.
Worksheet Answers Activity 2 (Standard demand) 1) Intense sunlight; little rainwater to dissolve the salt or reduce evaporation. 2) Fewer impurities; solution piped directly to factory; less labour intensive/automatic. 3) Students could access the Lion salt works website; answers could include an account of solution mining and a description of the evaporation process in open heated pans.
Worksheet Answers Activity 3 (High demand) 1) 33% 2)Benefits – reduced costs of travel; deaths/injuries prevented. Problems– costs to councils (unpredictable); environmental effect of mining and transport of salt; effects of salt on machinery and on wildlife on roadsides.
