Sunday, March 1, 2009

igcse/ gcse chemistry notes- Chemicals from salt

The electrolysis of aqueous sodium chloride solutionWhen the electrolysis of aqueous sodium chloride takes place, hydrogen and chlorine are given off as gases and sodium hydroxide is left. Aqueous sodium chloride contains hydrogen ions H+ and hydroxide ions OH- (from the water) and sodium ions Na+ and chloride ions Cl-. The positive sodium and hydrogen ions go to the cathode and the negative chloride and hydroxide ions go to the anode. Hydrogen is formed at the cathode and chlorine is formed at the anode.

test -lighted splint
result-squeaky pop

test-damp blue litmus
result-turns red then white

substance -sodium hydroxide
test-damp red litmus
result-turns blue/purple

Write a word and a balanced chemical equation for the reaction in which hydrogen burns.

Complete: Chlorine is (acidic/alkaline) because it turns litmus red. Chlorine is a (dye/bleach) because it turns litmus white. This type of reaction is (oxidation/reduction).

Uses of sodium chloride, hydrogen, chlorine and sodium hydroxide

sodium chloride
preserve food, flavouring, stops ice on roads because salt lowers freezing point of water to -5oC, manufacture of sodium, chlorine and sodium hydroxide

kills bacteria in swimming pools and drinking water, bleach, making hydrochloric acid and solvents.

rocket fuel, making margarine, making ammonia
sodium hydroxide
detergents, bleach, paper, fibres, purifying bauxite

Match the uses above to the explanations below: compounds of carbon and chlorine are good at dissolving grease, hydrogen reacts with chlorine to form hydrogen chloride, vegetable oil reacts with hydrogen to form margarine, nitrogen and hydrogen react together in the Haber process, soap is made from vegetable oil and sodium hydroxide, the structure of wood is broken up by sodium hydroxide, salt is easily detected by the tongue, bacteria cannot survive in salty solutions, by the electrolysis of molten sodium chloride, by the electrolysis of aqueous sodium chloride.

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