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.
(b)(i) A mixture of nitrogen (IV) oxide and oxygen is bubbled into warm water to produce trioxonitrate (V) oxide; write a balanced chemical equation for the reaction.
(ii) Using a balanced chemical equation, explain what would happen if only nitrogen (IV) oxide is bubbled into warm water.
(iii) Compare the gases evolved when trioxonitrate (V) acid decomposes, under each of the following properties: (I) pH; (II) Solubility in water; (III) Reaction with carbon (II) oxide.
(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.
(d) Name one calcium compound: (i) used to dry ammonia gas; (ii) used in the manufacture of cement; (iii) that causes hardness in water; (iv) referred to as plaster of paris.

Accepted Answer

(a)(i) Conditions used in the Haber process: Temperature of 350–500°C (high temperature); Pressure of 150–1000 atm (high pressure); Catalyst — finely divided iron.
(ii) Increasing the pressure increases the rate of reaction in the Haber process because the gas molecules are brought closer together, increasing the frequency of successful collisions per second.

(b)(i) 4NO2(g) + O2(g) + 2H2O(l) → 4HNO3(aq)
(ii) If nitrogen (IV) oxide alone is bubbled into warm water: 3NO2(aq) → 2NO2(g) + NO2(g)... more precisely: 3NO2(g) + H2O(l) → 2HNO3(aq) + NO(g). A mixture of two acids (a mixture of the acid and NO gas) would be produced.
(iii) Comparing oxygen and nitrogen(IV) oxide gases evolved: (I) pH — oxygen is neutral (pH=7) while NO2 is acidic (pH<7). (II) Solubility — NO2 is soluble in water while oxygen is only sparingly soluble. (III) Reaction with CO — O2 reacts with CO to form CO2, while NO2 reacts with CO to form a mixture of N2 and CO2.

(c)(i) Two oxides of sulphur: Sulphur (IV) oxide (SO2); Sulphur (VI) oxide (SO3).
(ii) SO2(g) + H2O(l) → H2SO3(aq); SO3(g) + H2O(l) → H2SO4(aq)

(d)(i) Used to dry ammonia gas: Calcium oxide (quicklime, CaO) — note: not calcium chloride, as it reacts with NH3.
(ii) Used in manufacture of cement: Calcium trioxocarbonate (IV) (CaCO3, limestone) / Calcium oxide (quicklime).
(iii) Causes hardness in water: Calcium hydrogentrioxocarbonate (IV), Ca(HCO3)2.
(iv) Referred to as plaster of paris: Calcium tetraoxosulphate (VI) dihydrate, CaSO4·2H2O.

WAEC Chemistry 2022 Theory — Question 6

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