Topic 4: Chemical Changes

• What is the reactivity series of metals? What are the trends in reactivities of metals in reactions with acids/water?


  • The series shows the metals in order of their reactivity.
  • Metals above H2 in reactivity series react with acid to produce H2. The more reactive the metal is, the quicker and more violent reaction with acid occurs.
  • Metals below H2 don’t react with acids.
  • Not all metals above H2 react with water - mostly Group I and II metals. Aluminium is the borderline case.
• The reactivity series of metals

  • Potassium
  • Sodium
  • Lithium
  • Calcium
  • Magnesium
  • Carbon
  • Zinc
  • Iron
  • Hydrogen
  • Copper
  • Gold

  
• How can metals less reactive than carbon be extracted?

  • Reduction with carbon.
  • Carbon displaces the metal in a metal oxide - gets oxidised to carbon oxides. 
  • Metal from the metal oxide gets reduced to the pure metal.
• Explain in terms of gain or loss of electrons which species has been oxidised and which species has been reduced when magnesium reacts with hydrochloric acid


  Magnesium has lost electrons and thus has been oxidised (Mg to Mg2+)

  The hydrogen in HCl has gained electrons and thus has been reduced (H+ to H2)
• How is a soluble salt formed?


  • React the excess acid with some insoluble chemical (e.g. metal oxide)
  • Filter off the leftovers
  • Crystallise the product
• What are bases, acids and alkalis?


  Bases are compounds that neutralise acids, acids produce hydrogen ions in aqueous solutions, alkalis are soluble bases - produce hydroxide ions in aqueous solutions
• What is a concentrated acid and what is a diluted acid? Is this the same as a strong and weak acid?


  • Concentrated acid has more moles of acid per unit volume than dilute (dilute refers to solutions of low concentrations)
  • It is not the same - concentration is not the same thing as strength of an acid.
  • Strength refers to whether the acid is completely ionised in water (strong) or only partially (weak).
• Name the following salts: LiNO3, K2CO3, MgBr2, BaSO4

  • Lithium nitrate
  • Potassium carbonate
  • Magnesium bromide
  • Barium sulfate
• What is electrolysis?


  The passing of an electric current through ionic substances that are molten or in solution to break them down into elements; ions are discharged (they lose/gain electrons) at electrodes to produce these
• In aqueous electrolysis, which element is discharged at the cathode? Oxygen is produced at the anode unless what?


  • The less reactive element discharges at the cathode. Hydrogen is produced unless there is a less reactive metal, in which case the said metal is produced.
  • Oxygen is produced at the anode unless the solution contains halide ions, in which case halogen molecules are produced.
• How is aluminium manufactured? Why is it expensive?

  • Aluminium is made through the electrolysis of aluminium oxide and cryolite.
  • Lots of energy is needed to produce the current in electrolysis which makes this process expensive.
• Metal oxides



  • Metals + oxygen -> metal oxides
  • Known as oxidation reactions because the metals gain oxygen
  • Reduction= loss of oxygen & oxidation= gain of oxygen
• OIL RIG , it stands for Oxidation Is Loss and Reduction Is Gain (of electrons)