Question 3
(a)(1) Describe briefly the laboratory preparation of hydrogen gas from the action of steam on iron.
(ii) Write the equation for the reaction in 3(a)(i).
(iii) List three methods for the industrial preparation of hydrogen gas. [9 marks]
(b)Consider the following reaction equation:
CO(g) + 2H2(g) CH3OH (g) + 201 kJmol-J
Predict the effect of each of the following factors on the position of equilibrium:
(i) decrease in temperature;
(ii) increase in pressure;
(iii) increase in concentration of CO(g). [3 marks]
(c) (i) Define condensation polymerization.
(ii) Name two condensation polymers.
(iii) Write the formula of ethylethanoate. [5 marls]
(d) (i) Define the term allotropy.
(ii) Name two crystalline allotropes of carbon.
(iii) State one use of each of the allotropes named in 3(d)(ii). [6 marks]
(e) State two differences between nitrogen (I) oxide and oxygen. [2 marks]
Observation
In part (a), majority of the candidates could not describe laboratory preparation of hydrogen gas from the action of steam on iron.
Also, majority of the candidates could not differentiate between laboratory and industrial methods of preparing hydrogen gas.
In part (b), performance of the candidates was good in this question. Majority of them applied correctly Le Chatelier’s principle in predicting the effect of the factors on the equilibrium position.
In part (c), majority of the candidates could not define condensation polymerization correctly and few of them named two condensation polymers. However, majority of the candidates wrote the correct formula of ethylethanoate.
In part (d), majority of the candidates defined the term allotropy correctly, and named two crystalline allotropes of carbon.
In part (e), majority of the candidates stated two differences between nitrogen (I) oxide and oxygen.
The expected answer include:
(a)(i) Heat the iron strongly in a combustion tube until it is red hot. Generate steam
by boiling water in a flask. Pass the steam over the red-hot iron. Hydrogen gas would be given off. Collect the hydrogen gas formed over water.
(ii) 3Fe(s) + 4H2O(g) Fe3O4(s) + 4H2(g)
(iii) - from water gas / Bosch process
- from methane
- by electrolytic method
- from catalytic cracking of petroleum products
(b) (i) It favours the backward reaction / Equilibrium position shifts to the left
(ii) Equilibrium position shifts to the right / favours the forward reaction
(iii) Equilibrium position shifts to the right / favours the forward reaction.
(c)(i) Condensation polymerization is defined as the linking together of monomers (with two different functional groups) to form a polymer with the elimination of a small molecule.
(ii) - Nylon/polyamide
- Terylene
- Silk
- Wool
- Cellulose
- Proteins
- Starch
- Dacron/polyester
- Phenol methanal
- Urea methanal
- Melamine methanal
(iii) - CH3COOC2H5
(d) (i) Allotropy is defined as the existence of two or more forms of an element in the same physical state.
(ii)- diamond
- graphite
(iii)
Diamond |
Graphite |
- jewellery |
- lubricant |
- drilling |
- black pigment in paints |
- cutting |
- electrical conductor for electrodes |
- abrasive |
- lead pencil |
- making of bearings |
- alloying |
- pivot support |
- neutron moderators |
- dies for drawing wires |
-lining of crucibles |
(e)
N2O |
O2 |
- pleasant smell |
- odourless |
- no reaction with NO |
- reacts with NO |
- produces N2/gas with heated |
- produces no N2/gas with heated copper |