4 - chemical changes

• Metal oxides


  Metals react with oxygen to produce metal oxides (oxidation)
• Reduction


  Loss of oxygen
• Oxidation


  Gain of oxygen
• Reduction


  Gain of electrons
• Oxidation


  Loss of electrons
• Reactivity series


  • Metal atoms lose an electron and form positive ions, when reacting
  • Reactivity - related to its tendency to form positive ions
• Metal + water


  Metal hydroxide + hydrogen
• Reactivity order


  • potassium
  • sodium
  • lithium
  • calcium
  • magnesium
  • zinc
  • iron
  • copper
• Non-metals hydrogen and carbon are often included in the reactivity series
• Unreactive metals


  • Found in the Earth
• Most metals


  • Found as compounds that require chemical reactions to extract
• A more reactive metal


  Can displace a less reactive metal from a compound
• Metals less reactive than carbon

  Can be extracted from their oxides by reduction with carbon
• Bases


  Mainly metal oxides/hydroxides, chemicals that neutralise acids (producing salt and water)
• Alkalis


  Bases that are soluble in water
• Acids + Alkalis


  Ions produce water (neutralisation)
• Acids


  • Hydrochloric acid (HCL)
  • Sulfuric acid (H2SO4)
  • Nitric acid (HNO3)
• Aqueous solutions


  Acids produce hydrogen ions (H+), alkalis produce hydroxide ions (OH-)
• Acids reacting with metals

  Produce salts and hydrogen gas (metals displace hydrogen from acid)
• Salts produced


  • Chloride
  • Sulfate
  • Nitrate
• Acids reacting with metal carbonates

  Produce salts, water and carbon dioxide
• Metal carbonates


  • Sodium carbonate
  • Calcium carbonate
  • Potassium carbonate
• Soluble salts


  Can be made from acids by reacting them with solid insoluble substances (metals, metal oxides, hydroxides or carbonates)
• Making soluble salts


  Solid is added to the acid until no more reacts, excess solid is filtered off (produce a solution of the salt)
• Salt solutions


  Can be crystallised to produce solid salts
• Acids


  Produce hydrogen ions (H+) in aqueous solutions (ionise)
• Alkalis


  Produce hydroxide ions (OH-) in aqueous solutions (ionise)
• pH scale


  Acids (0-6), neutral (7), alkalis (8-14)
• As pH decreases by 1 unit


  Concentration of hydrogen ions (and acidity) increases by ten times
• Strong acids


  Fully ionise (arrow in one direction)
• Weak acids


  Partially ionise (arrow in both directions)
• Dilute acid


  Has fewer acid molecules than concentrated (even when strength of acid is same)
• Electrolytes


  Liquids and solutions able to conduct electricity (inert)
• Electrolysis


  1. Electric current through electrolytes causes ions to move to the electrodes

  2. Positively charged ions (cations) move to the negative electrode (cathode)

  3. Negatively charged ions (anions) move to the positive electrode (anode)

  4. Ions are discharged at the electrodes (producing elements)
• Positive electrode (anode)


  • Must be continually replaced - graphite is a form of carbon, oxygen react with graphite to make carbon dioxide
• Electrolysis


  • Expensive - melting compounds and producing electric current requires a lot of energy
• Extracting metals by electrolysis


  Metals (more reactive than carbon) can be extracted from molten compounds using electrolysis
• Aluminium extraction


  • Large amounts of energy are used in the extraction process to melt the compounds and to produce the electrical current
• Electrolysis of aqueous solutions

  1. Water molecules break down producing hydrogen ions and hydroxide ions that are discharged

  2. Cathode (negative) - hydrogen is produced if the metal is more reactive than hydrogen

  3. Anode (positive) - oxygen is produced unless the solution contains halide ions (halogen)
• Cathode (negative)


  Positively charged ions gain electrons (reduction)