Cambridge IGCSE Chemistry - 0620 - Supplement Paper 4 2014 Summer Zone 3

Choose a gas from the following list to answer the questions below. Each gas may be used once, more than once or not at all.

ammonia carbon dioxide carbon monoxide fluorine
hydrogen krypton nitrogen propene sulfur dioxide

(a) It is a product of respiration. ............................................................... [1]
(b) It polymerises to form a poly(alkene). ........................................................ [1]
(c) It is a noble gas. ............................................................... [1]
(d) It is the main component of air. ............................................................... [1]
(e) It is a very reactive non-metal. ............................................................... [1]
(f) It is used to kill micro-organisms in fruit juice. ........................................................ [1]
(g) It burns to form water as the only product. ............................................................... [1]

Explain each of the following in terms of the kinetic particle theory.

(a) The rate of most reactions increases at higher temperatures.
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(b) A liquid has a fixed volume but takes up the shape of the container. A gas takes up the shape of the container but it does not have a fixed volume.

liquid                                    gas




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(a) Biological catalysts produced by microbes cause food to deteriorate and decay.
(i) What is the name of these biological catalysts?
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(ii) Freezing does not kill the microbes. Suggest why freezing is still a very effective way of preserving food.
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(b) Pea seeds grow in pods on pea plants.



Freshly picked pea seeds contain a sugar. The sugar can form a polymer.
Give the structural formula of the polymer and name the other product of this polymerisation reaction.
You may represent the sugar by the formula:

HO − ☐ − OH

structural formula of the polymer

other product ...................................................................................................................................................... [3]

(c) Describe how the pea plant makes a sugar such as glucose.
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(a) Calcium oxide and oxygen are used to remove the impurities from the iron produced in the blast furnace.

(i) State how these chemicals are manufactured.

calcium oxide .....................................................................................................................................
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oxygen ...............................................................................................................................................
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[3]

(ii) Describe how these two chemicals remove the four impurities. Include at least one equation in your answer.
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[5]

(b)
(i) Describe the structure of a typical metal such as iron. You may include a diagram.
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[2]

(ii) Explain why pure iron is malleable.
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[2]

(iii) Mild steel is an alloy of iron and carbon. Suggest why mild steel is harder than pure iron.
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[2]

Ammonia is made by the Haber process.
$$\text{N}_2(g) + 3\text{H}_2(g) \rightleftharpoons 2\text{NH}_3(g)$$
The forward reaction is exothermic. The conditions in the reaction chamber are:
• a pressure of 200 atmospheres,
• a catalyst of finely divided iron,
• a temperature of 400 to 450°C.
(a) What are the two advantages of using a high pressure? Give a reason for both.
advantage 1 ....................................................................................................................................
reason ..............................................................................................................................................
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advantage 2 ....................................................................................................................................
reason ..............................................................................................................................................
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(b) A higher temperature would give a faster reaction rate.
Why is a higher temperature not used?
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(c) (i) Why is the iron catalyst used as a fine powder?
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[1]
(ii) Give two reasons why a catalyst is used.
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(d) The equilibrium mixture leaving the reaction chamber contains 15% ammonia. Suggest how the ammonia could be separated from the mixture.
[Table_2]
boiling point /°C
hydrogen -253
nitrogen -196
ammonia -33
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(e) Ammonia is used to make nitrogen trifluoride, \text{NF}_3.
Nitrogen trifluoride is essential to the electronics industry. It is made by the following reaction.

Determine if the above reaction is exothermic or endothermic using the following bond energies and by completing the following table. The first line has been done as an example. Bond energy is the amount of energy, in kJ/mole, needed to break or make one mole of the bond.
[Table_3]
bond / bond energy in kJ/mole
N-H / 390
F-F / 155
N-F / 280
H-F / 565
[Table_4]
bond / energy change / kJ
N-H / (3 × 390) = 1170
F-F
N-F
H-F
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The alkanes are a family of saturated hydrocarbons. Their reactions include combustion, cracking and substitution.
(a) (i) What is meant by the term hydrocarbon? ............................................................................................................................................... [1]
(ii) What is meant by the term saturated? ............................................................................................................................................... [1]

(b) (i) What is the general formula for the homologous series of alkanes? ............................................................................................................................................... [1]
(ii) Calculate the mass of one mole of an alkane with 14 carbon atoms. ........................................................................................................................................................................ ........................................................................................................................................................................ [2]

(c) The complete combustion of hydrocarbons produces carbon dioxide and water only.
(i) Write the equation for the complete combustion of nonane, $C_9H_{20}$. ............................................................................................................................................... [2]
(ii) 20 $cm^3$ of a gaseous hydrocarbon was mixed with an excess of oxygen, 200 $cm^3$. The mixture was ignited. After cooling, 40 $cm^3$ of oxygen and 100 $cm^3$ of carbon dioxide remained. Deduce the formula of the hydrocarbon and the equation for its combustion. All volumes were measured at r.t.p.. ........................................................................................................................................................................ ........................................................................................................................................................................ ........................................................................................................................................................................ ........................................................................................................................................................................ ........................................................................................................................................................................ [3]

(d) Cracking is used to obtain short-chain alkanes, alkenes and hydrogen from long-chain alkanes.
(i) Give a use for each of the three products listed above.
short-chain alkanes ..................................................................................................................................
alkenes ..................................................................................................................................
hydrogen .................................................................................................................................. [3]
(ii) Write an equation for the cracking of decane, $C_{10}H_{22}$, which produces two different alkenes and hydrogen as the only products. ............................................................................................................................................... [1]

(e) Chlorine reacts with propane in a substitution reaction to form 1-chloropropane.
$CH_3-CH_2-CH_3 + Cl_2 \rightarrow CH_3-CH_2-CH_2-Cl + HCl$
(i) What is the essential condition for the above reaction? ............................................................................................................................................... [1]
(ii) There is more than one possible substitution reaction between chlorine and propane. Suggest the structural formula of a different product. ............................................................................................................................................... [1]

Aluminium is obtained from purified alumina, $Al_2O_3$, by electrolysis.
(a) Alumina is obtained from the main ore of aluminium. State the name of this ore.
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(b) Describe the extraction of aluminium from alumina. Include the electrolyte, the electrodes and the reactions at the electrodes.
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(c) Aluminium is resistant to corrosion. It is protected by an oxide layer on its surface. The thickness of this oxide layer can be increased by anodising.
(i) State a use of aluminium due to its resistance to corrosion.
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(ii) Anodising is an electrolytic process. Dilute sulfuric acid is electrolysed with an aluminium object as the anode. The thickness of the oxide layer is increased. Complete the equations for the reactions at the aluminium anode.
.......$OH^- ightarrow O_2 + 2H_2O + ......e^-$
....$Al + .......... ightarrow ..........Al_2O_3$ [4]