Question 4

The question was attempted by few candidates and the performance was good.
In (a)(i) and (ii), candidate were able to correctly write equations to represent the reactions as follows:                                                                 '
            (i)           24Na        24Mg + 0 B                                                                    ."
                             11                   12        -1

            (ii)        2N8(s) + 2H20 (s)          2Na0H(l) + H2(g)
In (b)(i) and (ii), only few candidates could state two differences between the reactions and two applications for (a)(i). The expected answers from candidates were:
(i)

Reaction I	Reaction ii
- takes place in the nucleus/nuclear reaction - large amount of heat is released - involves protons, neutrons and electrons - new nuclides are formed   - not affected by external factors e.g. 'temp     pressure,,catalyst	- takes place in the valence , shell/chemical reaction - small amount of'heat is released • involves     valence electrons     -new compounds are formed     -usually affected by external factor

-sterilizing instruments; -treatment of cancer; carbon dating;
-pest control etc.
In(c)(i) and (ii), candidates correctly named the reaction as displacement redox reaction and
  gave two ways by which the reaction could be made faster from the follow4J.g:         .
-           use Mg powder (increase surface area of Mg);
-           use HCI of higher concentration (Higher concentration of HC1);
-           increase temperature of the reaction mixture

. In (c)(iii), candidates were able to calculate the volume of hydrogen that would be produced from the given mass of Magnesium according to the reaction equation as follows:
                         24g Mg == 22.4dm30fH2(g)                   .
6gMg == 6gx22.4
                   24g
5.6dm3
In (d)(i) and (ii), candidates correctly defined an electrolytes and electrolysis as a compound which when in molten or aqueous solution will conduct electricity (and be decomposed by it) and the decomposition of an electrolyte by the passage of an electric current.
In (e), candidates correctly answered the question as follows:
(i) Aluminium;
(ii) Bauxite;
(iii) Cathode - Hydrogen;
(iv) Anode- Oxygen;

(v) In the liquid state the Na and Cl ions are mobile;
In the solid state the ions are in fixed positions arid cannot conduct electricity.
(vi) Industrial uses of NaCl
- In the manufacture of Cl2(g);
- salting out in soap manufacture;
-  Production of NaOH;
-  Solvay process/production of Na2C03.