CHEMICAL CHANGES

• How metal reacts with oxygen


  Forms metal oxide
• Gaining oxygen


  oxidation reaction
• Loss of oxygen


  Reduction reaction
• How do metals react with water

  -Potassium to lithium, react rapidly at room temp

  -Calcium, reacts quite rapidly at room temp

  -Magnesium to copper, no reaction at room temp
• Extraction of metals


  Unreactive metals found in the earth, e.g gold, but most found in compounds that need chemical reactions to extract.
• Oxidation in terms of electrons


  Loss of electrons (OIL)- Oxidation is loss
• Reduction in terms of electrons

  Gain of electrons(RIG)- Reduction is gain
• Acids


  substances that release hydrogen ions when dissolved in water
• Strong acids


  HCL, HS04, NO3

  Fully ionise in aqueous solutions.
• Weak acids


  Partially ionise in aqueous solution

  -ethanoic, carbonic and citric acid
• What happens to concentration when the ph scale decreases by one unit?

  -increases by ten times
• What order of magnitude is it when the pH is 100x stronger?

  Two orders of magnitude
• When is electrolysis used?

  When metals are more reactive than carbon
• Negative electrode


  Cathode(covered with electrons)
• Positive electrode


  anode (lack of electrons)
• Why do we add cryolite in the first stage of electrolysis of aluminium oxide?

  -lowers the melting point, reducing amount of energy needed and saves money.
• Why does the anode need to be replaced regularly?

  Oxygen molecules react with graphite(carbon), forming carbon dioxide gas
• Why is electrolysis so expensive?

  -melting compounds require a great deal of energy

  -a lot of energy required to produce a electric current
• When is hydrogen produced at the cathode?

  If the metal is more reactive than hydrogen
• What is used for electrodes in electrolysis of aqueous solutions?

  Platinum, because it's inert
• What will be produced at the anode if the aqueous solution contains halide ions?

  Halogen produced