(a)(i) Define allotropy. (ii) Name the allotrope of carbon used in gas masks. (iii) Mention two other elements which exhibit allotropy apart from carbon. (b...
Question 1 Report
(a)(i) Define allotropy.
(ii) Name the allotrope of carbon used in gas masks.
(iii) Mention two other elements which exhibit allotropy apart from carbon.
(b) List the products of each of the following reactions:
(i) Heating coal in the absence of air.
(ii) Burning of candle wax in plentiful supply of air
(c)(i) State the two properties of carbon (IV) oxide which make it useful in extinguishing fire.
(ii) Write an equation for the reaction of carbon (IV) oxide with lime water
(iii) Calculate the volume of oxygen that was in excess if 150cm\(^3\) of carbon (II) oxide was burnt in 80cm\(^3\) of oxygen according to the following equation: 2CO\(_{(g)}\) + O\(_{2(g)}\) \(\to\) 2CO\(_{2(g)}\).
(d)(i) State how nitrogen can be obtained from ammonia gas.
(ii) Name the gaseous fuels obtained when steam and air are passed over red hot coke.
(iii) Which of the fuels in (d)(ii) has the lower heating ability? Give reason for your answer.
Answer Details
(a)(i) Allotropy is the existence of an element in two or more different forms in the same physical state.
(a)(ii) Charcoal (activated carbon).
(a)(iii) Sulphur and phosphorus (also tin, oxygen).
(b) Products
- (i) Heating coal in the absence of air (destructive distillation): coke, coal gas, coal tar and ammoniacal liquor.
- (ii) Burning candle wax in plentiful air: carbon(IV) oxide (CO2) and water.
(c)(i) Carbon(IV) oxide is denser than air, so it settles over and blankets the fire, and it does not support combustion (it is non-flammable), cutting off oxygen.
(c)(ii)
\[ \text{CO}_2 + \text{Ca(OH)}_2 \to \text{CaCO}_3 + \text{H}_2\text{O} \]
(lime water turns milky).
(c)(iii) Volume of oxygen in excess
\( 2\text{CO} + \text{O}_2 \to 2\text{CO}_2 \), so CO : O2 = 2 : 1.
O2 required for 150 cm3 CO = \( \dfrac{150}{2} = 75\ \text{cm}^3 \).
Excess O2 = \( 80 - 75 = 5\ \text{cm}^3 \).
(d)(i) Pass ammonia over heated copper(II) oxide; the ammonia is oxidised, liberating nitrogen:
\[ 2\text{NH}_3 + 3\text{CuO} \to 3\text{Cu} + 3\text{H}_2\text{O} + \text{N}_2 \]
(d)(ii) Producer gas (from air over coke) and water gas (from steam over coke).
(d)(iii) Producer gas has the lower heating ability, because it contains a large proportion of non-combustible nitrogen which dilutes the combustible carbon(II) oxide, whereas water gas (CO + H2) is richer in combustible gases.
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