Question 4
- (a) (i) State two conditions used in the Haber process.
(ii) Explain briefly the effect of increasing the pressure on the rate of reaction in the
Haber process.
[5 marks]
(b) (i) A mixture of nitrogen (IV) oxide and oxygen is bubbled into warm water tp
produce trioxonitrate(V) oxide, write a balanced chemical equation for the reaction.
(ii) Using a balanced chemical equation only, explain what would happen if nitrogen
(IV) oxide is bubbled into warm water.
Compare the gases evolved when trioxonitrate (V) acid decomposes under each
of the following properties:
- pH;
- solubility in water;
- reaction with carbon (II) oxide.
[10 marks]
(c) (i) Name two oxides of sulphur.
(ii) Write a balanced equation for the reaction between each of the named oxides in
4(c)(i) and water.
Observation
In part (a), majority of the candidates stated two conditions used in the Haber process but could not explain the effect of increasing the pressure on the rate of reaction in the Haber process.
In part (b), majority of the candidates could not write a balanced chemical equation for the reaction.
In part (c), majority of the candidates named two oxides of sulphur.
In part (d), few candidates correctly named one calcium compound used to dry ammonia gas and in the manufacture of cement.
The expected answers include:
(a) (i) Temperature : 350 – 500oC / high temperature
Pressure : 150 – 1000 atm / high pressure
Catalyst : (Finely divided) Iron
(ii) Rate of the reaction increases as particles are closer together / more particles per unit volume. There are more collisions per second / collisions are more often
(b) (i) 4NO2 + O2 + 2H2O → 4HNO3
(ii) 2NO2 + H2O → HNO3 + HNO2
A mixture of two acids will be produced
(iii) 4HNO3(aq) → 4NO2(g) + O2(g) + 2H2O(l)
- Oxygen is neutral while NO2 is acidic / The pH of O2 is 7 while the pH of NO2 is less than 7.
- NO2 is soluble while O2 is sparingly soluble in water
- O2 reacts with CO to form CO2 while NO2 reacts with CO to form a mixture of N2 and CO2
(c) (i) - Sulphur (IV) oxide
- Sulphur (VI) oxide
(ii) SO2(g) + H2O(l) → H2SO3(aq)
SO3(g) + H2O(l) →H2SO4(aq)
(d) (i) - calcium oxide
- quick lime
(ii) - calcium trioxocarbonate (IV)
- limestone
- calcium oxide
- quick lime
(iii) - calcium tetraoxosulphate (VI)
- calcium hydrogen trioxocarbonate (IV)
- calcium chloride
(iv) Calcium tetraoxosulphate (VI) (dihydrate)
(v) Calcium tetraoxosulphate (VI) (dihydrate)