Question 5
(a) (i) Write an equation for the reaction by which sulphur dioxide in solution could be converted to tetraoxosulphate (VI) acid.(ii) State one test to confirm the conversion of sulphur dioxide to tetraoxosulphate (VI) acid.
(iii) State the reaction of concentrated tetraoxosulphate (VI) acid with:
(I) oxalic acid;
(II) copper.
(iv) What property of concentrated tetraoxosulphate (VI) acid does each of thereactions stated in 5 (a)(iii) illustrate? [11 marks]
(b) (i) Explain briefly why water is referred to as a universal solvent.
(ii) Give one chemical test for water. [5 marks]
(c) (i) What is the major component of synthetic gas?
(ii) Give one reason why synthetic gas is not a major source of air pollution.[2 marks]
(d) Name one product of destructive distillation of coal that is:
(i) solid;
(ii) liquid;
(iii) gas.
[3 marks] (e) (i) Write a balanced chemical equation for the complete combustion of carbon.
(ii) State one:
(I) physical;
(II) chemical property of the products in 5 (e)(i). [4 marks]
Observation
This question was popular among the candidates. Their performance in the question was average.In part (a), majority of the candidates could not write an equation for the reaction by which sulphur dioxide in solution could be converted to tetraoxosulphate (VI) acid.
In part (b), majority of the candidates could not explain why water is referred to as a universal indicator. However, they were able to give one chemical test for water.
In part (c), majority of the candidates were able to state the major component of synthetic gas.
In part (d), majority of the candidates were able to name one product of destructive distillation of coal that is solid, liquid and gas.
In part (e), majority of the candidates were able to write a balanced chemical equation for the complete combustion of carbon. However, only few of them could state one physical and chemical property of the products formed. The expected answers include:
OR
Add a solution of bariumtrioxonitrate (V), a white precipitate of bariumtetraoxosulphate (VI) is formed
II. H2SO4 is acting as an oxidizing agent
(b) (i) Water is referred to as a universal solvent because it is able to dissolve more substances than any other liquid. This has to do with the polarity of each water molecule. The hydrogen side of each water molecule carries a slight positive electric charge, while the oxygen side carries a slight negative electric charge and this helps water dissociate ionic compounds into their positive and negative ions.
(ii) Water will turn cobalt (II) chloride paper from blue to pink / anhydrous copper (II) tetraoxosulphate (VI) crystals from white to blue
(c) (i) CO / Carbon (II) Oxide
(ii) Because it is combustible / can be used as fuel
(d) (i) coke
(ii) coal tar / ammoniacal liquor / pitch
(iii) coal gas
(e) (i) C(s) + O2(g) →CO2(g)
(ii)
I.- It is odourless
- It is colourless
- It is denser than air
- It is soluble in water
- It is a gas at room temperature
- It is easily compressible
II. - It does not support combustion
- It reacts with red hot carbon (to form CO)
- it is weakly acidic in water
- it reacts with alkali (to form trioxocarbonate (IV) ) / turns lime water milky
- Reacts with burning magnesium