Acids

• Hydrochloric acid is produced in the stomach in order to:
  • help digestion
  •  kill bacteria
•  Indigestion remedies contain substances that neutralise excess stomach acid.
• acid+base -> salt + water
• If an indigestion tablet contains magnesium hydroxide, the neutralisation reaction is:
  • Hydrochloric acid + magnesium hydroxide -> megnesium chloride + water
• acid + carbonate -> salt + water + carbon dioxide
• For a tablet containing clacium carbonate, the neutralisation reaction will be:
  • Hydrochloric acid + calcium carbonate -> calcium chloride + water + carbon dioxide

• Acids are neutralise by:
  • metal oxides
  • metal hydroxides
  • metal carbonate to produce salts
• Hydrochloric acid produces chloride salts
• Nitric acid produces nitrate salts
• Sulphuric acid produces sulphate salts

• Electrolysis is a process in which electrical energy decomposes compounds
• You can test a gas to see if it is hydrogen by holding a lighted splint in mouth of a test tube containing gas. If hydrogen the mixture of hydrogen and air will explode with a squeaky 'pop'.
• You can test to see if it is chlorine by holding a piece of damp blue litmus paper in mouth of test tube. If the gas is chlorine it will turn red and then white (because it has been bleached)

The importance of chlorine

• Chlorine can be obtained from sea water by electrolysis
• Chlorine is a toxic gas, this leads to potential hazards associated with its large-scale manufacture. These include that:
  • It can leak accidentally from a chemical factory or if a tanker carrying the gas is involved in an accident
  • Many people could be killed or badly injured if it leaks near a town
• Chlorine is used:
  • to treat our water supply, killing organisms
  • in manufacturing bleach and other cleaning products
  • in the manufacture of plastics e.g. polychlorethene (PVC)

• Water can be decomposed by electrolysis to form hydrogen and oxygen
• To test for oxygen you:
  • light a splint and then blow out the flame so the end of the splint is just glowing
  • Put the splint in the mouth of the test tube,
  • if the gas is oxygen the splint will relight.