topic c4- chemical changes

• measure pH scale using

  • universal indicator (UI)- will turn one of the colours on the scale
  • pH probe
  • meter
• pH scale

  0

  1

  2

  3

  4

  5

  6

  7

  8

  9

  10

  11

  12

  13

  14
• acids

  • pH -> 0-6
  • examples:
  • battery acid
  • lemon juice
  • acid rain
• neutral

  • pH -> 7
  • example:
  • pure water
• alkalis

  • pH -> 8-14
  • examples:
  • bleach
  • soap powder
  • washing up liquid
• strong vs weak acids and alkalis

  • strong acid/ alkali ionises completely in water
  • release lots of H+ (acid) or OH- (alkali) ions
• reactivity series

  • how reactive different metals are (ordered)
  • reactivity is determined by how easily they lose electrons
  • carbon and hydrogen:
  • non-metals
  • how to extract metals based on relativity (ideas)
• acids

  • solution with pH lower than 7
  • form H+ ions in water
• alkalis

  • solution with pH higher than 7
  • form OH- ions in water
  • form of a base
• bases

  • any substance that will form a salt when reacted with acid
• water + metal

  metal hydroxide + hydrogen
• acid + metal

  salt + hydrogen
• neutralisation reactions

  form salt and water
• acid + base

  salt + water
• acid + metal oxide

  salt + water
• acid + metal hydroxide

  salt + water
• acid + metal carbonate

  salt + water + carbon dioxide
• • metal oxides, metal hydroxides + metal carbonates are bases
  • so all produce salt and water with acid
  • neutralisation reaction
• salts

  • sulphuric acid creates sulphates
  • nitric acid creates nitrates
  • hydrochloric acid creates chlorides
• reactivity series

  potassium -> most reactive

  sodium

  lithium

  calcium

  magnesium

  aluminium

  CARBON

  zinc

  iron

  HYDROGEN

  copper

  silver

  gold -> least reactive
• redox reactions

  electrons are transferred
• oxidation

  • loss of electrons
  • gain of oxygen
• reduction

  • gain of electrons
  • loss of oxygen
• O xidation

  I s

  L oss

  R eduction

  I s

  G ain

  • of electrons
• redox/ displacement reaction

  Fe + CuSO4 -> FeSO4 + Cu

  • iron is more reactive than copper
  • so iron displaces the copper
• electrolysis equipment

  • cathode
  • anode
  • d.c. power supply
  • electrolyte
  • molten metal
• cathode

  negative electrode
• anode

  positive electrode
• electrolysis

  • molten ionic compounds entered into the container, this is the electrolyte
  • the positive metal ions are attracted to the cathode where they gain electrons, become neutral and sink
  • the negative ions are attracted to the anode and lose electrons and rise
• displacement reaction

  a reaction in which a more reactive metal or non-metal will take the place of another in an ionic compound
• electrolysis- anode

  • lose electrons
  • oxidation
  • attract negative ions
• electrolysis- cathode

  • gain electrons
  • attract positive ions
  • reduction
• anode- products

  • oxygen gas- when no halogens
  • if halogens- halogen gas instead ~
• cathode- products

  • metal more reactive than hydrogen- hydrogen gas
  • metal less reactive than hydrogen- metal is deposited/ forms a solid