Question 4
- (i) In the laboratory preparation of dry chlorine gas, state the:
- reagents used;
- drying agent used;
- the mode of collection.
- (i) Name the main raw materials used for the extraction of iron in the blast furnace.
- The following equation represents one of the reaction steps involved in the contact process:
- Why is the SO3produced during the reaction not dissolved directly in water to form H2SO4?
- Why is H2SO4 regarded as a heavy chemical?
- State the property exhibited by tetraoxosulphate (VI) acid in each of the following reaction equations.
- Pb(NO3)2(aq) + H2SO4(aq) PbSO4(s) + 2HNO3(aq)
- H2S(g) + H2SO4(aq) S(s) + 2H2O(l) + SO2(g)
- Write a balanced chemical equation for the reaction between propanol and sodium.
(iI)Write the equation for the preparation of chlorine gas
(iII)Write an equation to show how chlorine reacts with hot concentrated NaOH.
[7 marks]
(ii) Write the equations of the reaction taking place in the blast furnace.
(iii) What is the name given to the iron obtained directly from the blast furnace?
[11 marks]
2SO2(g) + O2(g) 2SO3(g) H = -395.7 kJ mol-1
[5 marks]
[2 marks]
Observation
This question was not popular among the candidates as majority of them avoided it.
In part (a), majority of candidates were able to state the reagents used for the laboratory preparation of dry chlorine gas. However, they could not write the equation for the preparation of the gas.
In part (b), some candidates that attempted this question wrote the formulae of the main raw materials used for the extraction of iron in the blast furnace instead of names. In addition to this, they could not write the equations of the reactions taking place in the blast furnace.
In part (c), majority of the candidates could not state why SO3 produced during contact process was not dissolved directly in water to form H2SO4. However, they gave a reason why H2SO4 is regarded as a heavy chemical.
In part (d), majority of the candidates could not write a balanced chemical equation for the reaction between propanol and sodium.
The expected answers include:
(a) (i) I. Conc. HCl and MnO2/ KMnO4
II. (Conc). H2SO4
III. Downward delivery / upward displacement of air
(ii) 16HCl(aq) + 2KMnO4(aq) → 2MnCl2(aq)+ 2KCl(aq) + 8H2O(l) + 5Cl2(g)
OR
MnO2 + 4HCl MnCl2 + 2H2O + Cl2
(iii) 3Cl2(g) + 6NaOH(aq) → 5NaCl(aq)+ NaClO3(aq) + 3H2O(l)
(b)
(i)
- Haematite
- Coke
- Limestone
(ii) C + O2 → CO2
C + CO2 → 2CO
Fe2O3 + 3CO 2Fe + 3CO2
CaCO3 → CaO + CO2
CaO + SiO2 → CaSiO3
(iii) Pig iron
(iv) because it contains impurities / not pure
(c)
(i) The dissolution of SO3 in water is highly exothermic
mist of acid droplets would be formed
(ii) - It is produced on a large scale
- It is required by many industries as a raw material
- it is in high demand by other industries
(iii)
I. acting as a displacement / precipitating agent
II. acting as an oxidizing agent
(d) 2CH3CH2CH2OH + 2Na → 2CH3CH2CH2ONa + H2
OR
2C3H7OH+ 2Na → 2C3H7ONa + H2