(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.
Explanation
(a)(i) Allotropy is defined as the existence of an element in two or more forms in the same physical state.
(ii) The form of carbon used in gas mask is amorphous carbon/wood charcoal / graphite.
(iii) Other elements which exhibit allotropy are sulphur, phosphorus, oxygen, tin, etc.
(b)(i) Products of heating coal in the absence of air are coal gas, coal tar, ammoniacal liquor, coke.
(ii) Products of burning candle wax in plentiful supply of air are CO\(_2\) and steam/H\(_2\)O.
(c)(i) - It does not support combustion
- It is heavier I denser than air
(ii) CO\(_2\) + Ca(OH)\(_2\) --> CaCO\(_2\) + H\(_2\)O Or 2CO\(_2\) + Ca(OH)\(_2\) —> Ca(HCO\(_3\))\(_2\).
(iii) 2CO\(_{(g)}\) + O\(_{2(g)}\) --> 2CO\(_{2(g)}\). From the equation and according to Gay Lussac's law, 2 volumes of CO react with 1 volume of O\(_2\), 150 cm\(^3\) of CO react with 75cm\(_2\) of O\(_2\). Excess O\(_2\) = (80 - 75)cm\(_3\) = 50cm\(_3\).
(d) Nitrogen can be obtained from ammonia
(i) By passing NH\(_3\) over copper (II) oxide or by oxidation or reaction with chlorine. i.e. 3CuO + 2NH\(_3\) -> 3Cu _ 3H\(_2\)O + N\(_2\) Or 8NH + 3Cl\(_2\) —> 6NH\(_4\)CI + N\(_2\).
(ii) Water gas and producer gas are obtained when steam and air are passed over red hot coke
(iii) Producer gas has a lower heating ability than water gas. Reason: Water gas consists of equal volumes of and Cu both of which are combustible whereas producer gas consists of CO and N\(_2\) only one of which s combustible.