(a)
(i) List two gaseous pollutants that can be generated by burning coal.
(ii) Explain briefly why coal burns more easily when it is broken into pieces than when it is in lumps.
(iii) What gas is responsible for most of the explosions in coal mines?
(iv) Name the non-volatile residue left behind after the destructive distillation of coal.
(b) State one oxide in each case which:
(i) is used in bleaching;
(ii) oxidizes hot concentrated HCl to chlorine;
(iii) dissolves in water to give a solution with pH greater than 7;
(iv) reacts with NaOH and also with HCl;
(v) is a reddish-brown gas.
(c)
(i) Write a balanced chemical equation for the reaction between chlorine gas and iron(II) chloride solution.
(ii) State the type of reaction in (c)(i).
(iii) Give a reason for your answer in (c)(ii).
(d) Consider the following set-up: 
(i) Identify A and B.
(ii) Write a balanced chemical equation for the reaction.
(iii) Name the gas produced.
(iv) Why was the flask tilted downwards?
(v) What is the:
(I) function of B in the experiment;
(II) method of collection of the gas?
(e) Give one product obtained from refining petroleum that is solid.
(a) Coal
(i) Two gaseous pollutants produced by burning coal are sulphur(IV) oxide, \(SO_2\) and carbon(II) oxide (carbon monoxide), \(CO\). (Oxides of nitrogen, \(NO_x\), are also acceptable.)
(ii) Breaking coal into pieces greatly increases the total surface area of solid exposed to the oxygen of the air. Combustion is a surface reaction, so a larger area of contact means more collisions per second between the coal and oxygen molecules. The rate of burning therefore rises, and the broken coal ignites and burns more easily than the same mass held in one large lump.
(iii) Methane, \(CH_4\) (called firedamp) is responsible for most explosions in coal mines.
(iv) The non-volatile residue left after the destructive distillation of coal is coke.
(b) Oxides
| Property | Oxide |
|---|
| (i) used in bleaching | Sulphur(IV) oxide, \(SO_2\) |
| (ii) oxidises hot concentrated HCl to chlorine | Manganese(IV) oxide, \(MnO_2\) |
| (iii) dissolves in water to give a solution of pH > 7 | Sodium oxide, \(Na_2O\) (basic oxide) |
| (iv) reacts with both NaOH and HCl | Aluminium oxide, \(Al_2O_3\) (amphoteric) |
| (v) is a reddish-brown gas | Nitrogen(IV) oxide, \(NO_2\) |
The reaction in (ii) is:
\[MnO_2 + 4HCl \rightarrow MnCl_2 + Cl_2 + 2H_2O\]
(c) Chlorine and iron(II) chloride
(i) \[2FeCl_2 + Cl_2 \rightarrow 2FeCl_3\]
(ii) It is a redox (oxidation-reduction) reaction.
(iii) The iron is oxidised while the chlorine is reduced in the same reaction. \(Fe^{2+}\) loses one electron to become \(Fe^{3+}\) (oxidation), and each atom of the added chlorine gains an electron, changing from oxidation state \(0\) in \(Cl_2\) to \(-1\) in the chloride (reduction). Since oxidation and reduction occur together, the reaction is redox.
(d) The set-up shown
The diagram shows a round-bottom flask containing a mixture of calcium hydroxide, \(Ca(OH)_2\), and ammonium chloride, \(NH_4Cl\), mounted on a stand and heated with a burner. The flask is clamped so that its mouth points slightly downwards. A delivery tube A carries the gas evolved into a vertical tower B which is packed with granular solid, and the gas is finally collected in an inverted gas jar at the top.
(i) A is the delivery tube (which conveys the gas from the flask). B is a drying tower (drying column) packed with lumps of calcium oxide (quicklime), \(CaO\).
(ii) \[2NH_4Cl + Ca(OH)_2 \rightarrow CaCl_2 + 2NH_3 + 2H_2O\]
(iii) The gas produced is ammonia, \(NH_3\).
(iv) The flask was tilted with its mouth downwards so that the water (steam) formed in the reaction condenses near the cooler mouth and does not run back onto the hot base of the flask. If cold water ran onto the strongly heated glass, the sudden contraction would crack the flask.
(v)(I) The function of B is to dry the ammonia gas. The calcium oxide absorbs the water vapour carried over from the flask; ordinary drying agents such as concentrated \(H_2SO_4\) or anhydrous \(CaCl_2\) cannot be used because they react with the alkaline ammonia, so the basic drying agent \(CaO\) is used.
(v)(II) The gas is collected by downward displacement of air (upward delivery into an inverted gas jar). Ammonia is used this way because it is less dense than air and is very soluble in water, so it cannot be collected over water.
(e) Solid product from refining petroleum
A solid product obtained from refining petroleum is bitumen (asphalt). (Paraffin wax is also acceptable.)
(a) Coal
(i) Two gaseous pollutants produced by burning coal are sulphur(IV) oxide, \(SO_2\) and carbon(II) oxide (carbon monoxide), \(CO\). (Oxides of nitrogen, \(NO_x\), are also acceptable.)
(ii) Breaking coal into pieces greatly increases the total surface area of solid exposed to the oxygen of the air. Combustion is a surface reaction, so a larger area of contact means more collisions per second between the coal and oxygen molecules. The rate of burning therefore rises, and the broken coal ignites and burns more easily than the same mass held in one large lump.
(iii) Methane, \(CH_4\) (called firedamp) is responsible for most explosions in coal mines.
(iv) The non-volatile residue left after the destructive distillation of coal is coke.
(b) Oxides
| Property | Oxide |
|---|
| (i) used in bleaching | Sulphur(IV) oxide, \(SO_2\) |
| (ii) oxidises hot concentrated HCl to chlorine | Manganese(IV) oxide, \(MnO_2\) |
| (iii) dissolves in water to give a solution of pH > 7 | Sodium oxide, \(Na_2O\) (basic oxide) |
| (iv) reacts with both NaOH and HCl | Aluminium oxide, \(Al_2O_3\) (amphoteric) |
| (v) is a reddish-brown gas | Nitrogen(IV) oxide, \(NO_2\) |
The reaction in (ii) is:
\[MnO_2 + 4HCl \rightarrow MnCl_2 + Cl_2 + 2H_2O\]
(c) Chlorine and iron(II) chloride
(i) \[2FeCl_2 + Cl_2 \rightarrow 2FeCl_3\]
(ii) It is a redox (oxidation-reduction) reaction.
(iii) The iron is oxidised while the chlorine is reduced in the same reaction. \(Fe^{2+}\) loses one electron to become \(Fe^{3+}\) (oxidation), and each atom of the added chlorine gains an electron, changing from oxidation state \(0\) in \(Cl_2\) to \(-1\) in the chloride (reduction). Since oxidation and reduction occur together, the reaction is redox.
(d) The set-up shown
The diagram shows a round-bottom flask containing a mixture of calcium hydroxide, \(Ca(OH)_2\), and ammonium chloride, \(NH_4Cl\), mounted on a stand and heated with a burner. The flask is clamped so that its mouth points slightly downwards. A delivery tube A carries the gas evolved into a vertical tower B which is packed with granular solid, and the gas is finally collected in an inverted gas jar at the top.
(i) A is the delivery tube (which conveys the gas from the flask). B is a drying tower (drying column) packed with lumps of calcium oxide (quicklime), \(CaO\).
(ii) \[2NH_4Cl + Ca(OH)_2 \rightarrow CaCl_2 + 2NH_3 + 2H_2O\]
(iii) The gas produced is ammonia, \(NH_3\).
(iv) The flask was tilted with its mouth downwards so that the water (steam) formed in the reaction condenses near the cooler mouth and does not run back onto the hot base of the flask. If cold water ran onto the strongly heated glass, the sudden contraction would crack the flask.
(v)(I) The function of B is to dry the ammonia gas. The calcium oxide absorbs the water vapour carried over from the flask; ordinary drying agents such as concentrated \(H_2SO_4\) or anhydrous \(CaCl_2\) cannot be used because they react with the alkaline ammonia, so the basic drying agent \(CaO\) is used.
(v)(II) The gas is collected by downward displacement of air (upward delivery into an inverted gas jar). Ammonia is used this way because it is less dense than air and is very soluble in water, so it cannot be collected over water.
(e) Solid product from refining petroleum
A solid product obtained from refining petroleum is bitumen (asphalt). (Paraffin wax is also acceptable.)
