A Level: Worksheet: Group II – Magnesium and Calcium

Worksheet 11.1

Group II – magnesium and calcium

1    Magnesium metal is used in the production of titanium. Over 80 000 tonnes of titanium metal
are produced per year. Most of this is used to make aircraft, in particular to make engine parts for modern jets. Titanium is produced in two stages. Firstly, the titanium ores are used
to make titanium tetrachloride, TiCl₄, which is a liquid. Secondly, magnesium metal is added
to the titanium tetrachloride and these two chemicals react to make titanium and magnesium chloride. The magnesium chloride is electrolysed.

a    Do you expect the structure of titanium tetrachloride to be giant ionic or simple covalent?
       Give a reason for your answer.                                                                                        [2]

b    Write an equation for the reaction of magnesium with titanium tetrachloride.                 [2]

c    What are the oxidation states (oxidation numbers) of magnesium, titanium and chlorine
      before and after this reaction?                                                                                         [3]

d    Which element is oxidised in this reaction and which element is reduced?                     [2]

e    When the magnesium chloride is electrolysed, magnesium and chlorine are formed.
      Write a half-equation for the formation of magnesium from magnesium ions.                [2]

f     Is magnesium oxidised or reduced in this process?                                                         [1]

g    What large-scale use could be made of the chlorine within the titanium production plant? [1]

2    A lot of limestone (CaCO₃) is quarried in the UK. The limestone can then be heated in lime kilns
to make lime (CaO). If water is added to lime, they react to make slaked lime (Ca(OH)₂), which
is used extensively in agriculture. Slaked lime is not very soluble in water, but its solution,
known as limewater, is useful. If carbon dioxide gas is bubbled into lime water, the limewater goes cloudy at first; but if the carbon dioxide gas keeps on being added, the limewater will eventually go clear again.

a    Write a balanced chemical equation for the reaction in which lime is produced from
       limestone.                                                                                                                        [2]

b    Write a balanced chemical equation for the reaction in which slaked lime is produced
      from lime.                                                                                                                       [2]

c    Explain why ‘slaked lime is used extensively in agriculture’.                                         [1]

d    What chemical property of slaked lime is important here?                                              [1]

e    Write a balanced chemical equation for the first reaction between limewater and carbon dioxide.  Include state symbols.                                                                                                                  [3]