(a)(i) Describe briefly the industrial preparation of ammonia. (ii) Write a balanced equation for the reaction in (a)(i). (iii) State one way of increasing ...

Answer Details

(a)(i) Industrial preparation of ammonia (Haber process): nitrogen (from air) and hydrogen (from natural gas) are mixed in the ratio 1:3 and passed over a finely divided iron catalyst at about 450 °C and about 200 atmospheres pressure.

(ii) \[N_2 + 3H_2 \rightleftharpoons 2NH_3\]

(iii) Increase the yield by increasing the pressure (or by lowering the temperature, or removing ammonia as it forms).

(iv) Uses of ammonia: manufacture of fertilizers (ammonium salts) and manufacture of trioxonitrate(V) acid.

(b) Chemical tests

• (i) Hydrogen: a lighted splint applied to the gas burns it with a squeaky "pop" sound.
• (ii) Carbon(IV) oxide: the gas turns limewater (calcium hydroxide solution) milky.
• (iii) Oxygen: the gas rekindles (relights) a glowing splint.

(c)(i) Water gas is a mixture of carbon(II) oxide and hydrogen (CO + H₂).

(ii) Uses of water gas: as a fuel; as a source of hydrogen in industry (for example in the manufacture of methanol/ammonia).

(d) Type of hardness: boil a sample of the water and then add soap solution. If the water now lathers readily (hardness removed by boiling), the hardness is temporary. If it still does not lather easily after boiling, the hardness is permanent. Comparing lathering before and after boiling distinguishes the two.