Question

When heated in air, magnesium ribbon reacts with oxygen to form magnesium oxide.
    (a) (i) Write a balanced equation for the reaction that occurs.                                                                                                         [1]

             (ii) Identify a metal, in the same period as magnesium, that does not form a
                 basic oxide.                                                                                                                                                                                     [1]

      (b) The reaction in (a)(i) was carried out in a crucible with a lid and the following data
           was recorded:
                                                                            Mass of crucible and lid = 47.372 ±0.001g
            Mass of crucible, lid and magnesium ribbon before heating = 53.726 ±0.001g
                                    Mass of crucible, lid and product after heating = 56.941 ±0.001g

           (i) Calculate the amount of magnesium, in mol, that was used.                                                                                                [1]

                (ii) Determine the percentage uncertainty of the mass of product after heating.                                                                [2]

                (iii) Assume the reaction in (a)(i) is the only one occurring and it goes to completion,
                     but some product has been lost from the crucible. Deduce the percentage yield of
                      magnesium oxide in the crucible.                                                                                                                                         [2]

      (c) When magnesium is burnt in air, some of it reacts with nitrogen to form magnesium
            nitride according to the equation:
                                                                         3 Mg(s) + N₂ (g) → Mg₃N₂ (s)

           (i) Evaluate whether this, rather than the loss of product, could explain the yield
                 found in (b)(iii).                                                                                                                                                                              [1]

             (ii) Suggest an explanation, other than product being lost from the crucible or
                 reacting with nitrogen, that could explain the yield found in (b)(iii).                                                                                [1]

       (d) The presence of magnesium nitride can be demonstrated by adding water to the
           product. It is hydrolysed to form magnesium hydroxide and ammonia.

           (i) Calculate coefficients that balance the equation for the following reaction.                                                                      [1]

           (ii) Ammonia is added to water that contains a few drops of an indicator. Identify an
                  indicator that would change colour. Use sections 21 and 22 of the data booklet.                                                           [1]

              (iii) Determine the oxidation state of nitrogen in Mg₃N₂ and in NH₃.                                                                                     [1]

            (iv) Deduce, giving reasons, whether the reaction of magnesium nitride with water is
                     an acid–base reaction, a redox reaction, neither or both.                                                                                                 [2]

     (e) Most nitride ions are ¹⁴N^3- .

           (i) State the number of subatomic particles in this ion.                                                                                                               [1]

           (ii) Some nitride ions are ¹⁵N^3-. State the term that describes the relationship between ¹⁴N^3- and ¹⁵N^3-.                        [1]

              (iii) The nitride ion and the magnesium ion are isoelectronic (they have the same
                    electron configuration). Determine, giving a reason, which has the greater
                    ionic radius.                                                                                                                                                                                  [1]

               (iv) Suggest, giving a reason, whether magnesium or nitrogen would have the greater
                   sixth ionization energy.                                                                                                                                                                [1]

         (f) Suggest two reasons why atoms are no longer regarded as the indivisible units of matter.                                                [2]

        (g) State the types of bonding in magnesium, oxygen and magnesium oxide, and how the
           valence electrons produce these types of bonding.                                                                                                                        [4]