acids and bases- chemical changes

• acid


  has H^+ ions (e.g. HNO`3, H`2SO`4)
• alkali


  SPCA oxide/ hydroxide (sodium/ potasssium/ calcium/ ammonium, OH^-, O^2-)
• base


  non-SPCA oxide/ hydroxide (OH^-, O^2-)
• salt


  ionic compound (metal+ non-metal, cation+ anion) (e.g. NaNO`3, MgCO`3, MgCl`2)
• acid definition

  an acid is a substance that ionizes to produce hydrogen ions (H^+ ions) when dissolved in water
• acid physical properties

  • sour taste
  • can conduct electricity when dissolved in water
  • AT: there are mobile hydrogen ions that are able to act as mobile charge carriers so acid is able to conduct electricity
  • turns blue litmus paper blue, red litmus paper remains red
  • concentrated acids are corrosive while diluted acids are irritants
• acid uses

  agricultural fertilisers, detergents, paints, dyes, artificial fibres, remove rust, food preservation
• bases definition

  a substance which reacts with an acid to form a salt, metal oxide/ hydroxide
• bases consist of...

  alkalis: SPCA+ hydoxide/ oxide (dissolves in water)

  other bases: metal oxide/ hydroxide (does not dissolve in water)
• bases physical properties

  • bitter taste
  • slippery
  • alkalis but not bases can conduct electricity in water
  • AT: there are mobile hydroxide ions that are able to act as mobile charge carriers so alkali is able to conduct electricity
  • turns red litmus paper blue, blue litmus paper remains blue
  • concentrated alkalis are corrosive and diluted alkalis are irritants
• bases uses

  sodium hydroxide is used in soaps and detergents, ammonia solution is used in window cleaners and nitrogenous fertilisers, calcium oxide, calcium hydroxide and calcium carbonate are used in neutralising acidic soil, magnesium hydroxide used in toothpaste to neutralise acids for our teeth
• *acid+ reactive metal -> salt+ hydrogen gas (unreactive metals: silver, gold, platinum, copper)


  • observations:
  • efferversence of a colourless and odourless gas will be observed
  • temp increases
  • metal decreases in size/ completely dissolved in acid
  • test for gas
  • place a lighted splint into a test tube containing the gas, if the lighted splint extinguishes with a "pop" sound, the gas is hydrogen
• *acid+ carbonate -> salt+ carbon dioxide+ water


  • observations:
  • efferversence of a colourless and odourless gas will be observed
  • test for gas
  • bubble the gas through aqueous calcium hydroxide (limewater). If a white precipitate is formed, the gas is carbon dioxide
• *acid+ base -> salt + water


  • observations:
  • temp increases
• *base + ammonium salt -> salt + ammonia gas + water


  • observations:
  • efferversence of a colourless and pungent gas will be observed on warming the solution
  • test for gas:
  • place a piece of moist red litmus paper at the mouth of the test tube containing the gas. if the moist red litmus paper turns blue, the gas is ammonia