Cambridge IGCSE Chemistry - 0620 - Supplement Paper 4 2013 Summer Zone 1

Petroleum contains hydrocarbons which are separated by fractional distillation.
(a) (i) Complete the following definition of a hydrocarbon.
A hydrocarbon is a compound which ..............................................................
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(ii) Explain what is meant by the term fractional distillation.
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(b) Some of the fractions obtained from petroleum are given below. State a use for each fraction.
bitumen ........................................................
lubricating fraction ........................................................
paraffin fraction ........................................................
gasoline fraction ........................................................ [4]

An element, M, has the electron distribution 2 + 8 + 18 + 3.

(a) Which group in the Periodic Table is element M likely to be in?
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(b) Predict whether element M is a poor or a good conductor of electricity. Give a reason for your answer.
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(c) Binary compounds contain two atoms per molecule, for example HCl. Identify an element which could form a binary compound with element M.
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(d) Predict the formula of the sulfate of M. The formula of the sulfate ion is $\text{SO}_4^{2-}$.
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(e) The hydroxide of M is a white powder which is insoluble in water. Describe how you could show that this hydroxide is amphoteric.
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A small piece of marble, CaCO\(_3\), was added to 5.0 cm\(^3\) of hydrochloric acid, concentration 1.0 mol/dm\(^3\), at 25\(^{\circ}\)C. The time taken for the reaction to stop was measured. The experiment was repeated using 5.0 cm\(^3\) of different solutions of acids. The acid was in excess in all of the experiments.

Typical results are given in the table.

[Table_1]
experiment | temperature / \(^{\circ}\)C | acid solution | time / min
1 | 25 | hydrochloric acid 1.0 mol/dm\(^3\) | 3
2 | 25 | hydrochloric acid 0.5 mol/dm\(^3\) | 7
3 | 25 | ethanoic acid 1.0 mol/dm\(^3\) | 10
4 | 15 | hydrochloric acid 1.0 mol/dm\(^3\) | 8

(a) (i) Explain why it is important that the pieces of marble are the same size and the same shape.
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(ii) How would you know when the reaction had stopped?
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(b) The equation for the reaction in experiment 1 is:
CaCO\(_3\)(s) + 2HCl(aq) \(\rightarrow\) CaCl\(_2\)(aq) + CO\(_2\)(g) + H\(_2\)O(l)
Complete the following ionic equation.
CaCO\(_3\)(s) + 2H\(^+\)(aq) \(\rightarrow\) ............ + ............ + ............ [1]

(c) (i) Explain why the reaction in experiment 1 is faster than the reaction in experiment 2.
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(ii) The acids used for experiment 1 and experiment 3 have the same concentration. Explain why experiment 3 is slower than experiment 1.
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(iii) Explain in terms of collisions between reacting particles why experiment 4 is slower than experiment 1.
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The structural formula of cyclohexane is drawn below.

(a) The name gives information about the structure of the compound.
Hex because there are six carbon atoms and cyclo because they are joined in a ring.
What information about the structure of this compound is given by the ending ane?
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(b) What are the molecular and empirical formulae of cyclohexane?
molecular formula ................................
empirical formula .................................
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(c) Draw the structural formula of cyclobutane.

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(d) (i) Deduce the molecular formula of hexene.
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(ii) Explain why cyclohexane and the alkene, hexene, are isomers.
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(e) Describe a test which would distinguish between cyclohexane and the unsaturated hydrocarbon hexene.
test ..................................................................................................................................................
result of test with cyclohexane ...............................................................................................
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result of test with hexene ......................................................................................................
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The reactivity series shows the metals in order of reactivity.

(a) The reactivity series can be established using displacement reactions. A piece of zinc is added to aqueous lead nitrate. The zinc becomes coated with a black deposit of lead.

Zn + Pb^{2+} \rightarrow Zn^{2+} + Pb

Zinc is more reactive than lead.

The reactivity series can be written as a list of ionic equations.

...... \rightarrow ...... + ...... most reactive metal: the best reductant (reducing agent)

Zn \rightarrow Zn^{2+} + 2e^{-}
Fe \rightarrow Fe^{2+} + 2e^{-}
Pb \rightarrow Pb^{2+} + 2e^{-}
Cu \rightarrow Cu^{2+} + 2e^{-}
Ag \rightarrow Ag^{+} + e^{-}

(i) In the space at the top of the list, write an ionic equation for a metal which is more reactive than zinc. [1]

(ii) Write an ionic equation for the reaction between aqueous silver(I) nitrate and zinc. [2]

(iii) Explain why the positive ions are likely to be oxidants (oxidising agents). [1]

(iv) Deduce which ion is the best oxidant (oxidising agent). [1]

(v) Which ion(s) in the list can oxidise lead metal? [1]

(b) A reactivity series can also be established by measuring the voltage of simple cells. The diagram shows a simple cell.



Results from cells using the metals tin, cadmium, zinc and copper are given in the table below.

[Table_1]
| cell | electrode 1 positive electrode | electrode 2 negative electrode | voltage / volts |
|------|---------------------------------|-------------------------------|----------------|
| 1 | copper | cadmium | 0.74 |
| 2 | copper | tin | 0.48 |
| 3 | copper | zinc | 1.10 |

Write the four metals in order of increasing reactivity and explain how you used the data in the table to determine this order. [3]

Ammonia is a compound which only contains the elements nitrogen and hydrogen. It is a weak base.
(a) (i) Define the term base.
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(ii) Given aqueous solutions of ammonia and sodium hydroxide, both having a concentration of 0.1 mol/dm$^3$, how could you show that ammonia is the weaker base?
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(b) Ammonia is manufactured by the Haber Process. The economics of this process require that as much ammonia as possible is made as quickly as possible. Explain how this can be done using the following information. The conditions for the following reversible reaction are:
• 450°C
• 200 atmospheres pressure
• iron catalyst
$N_2(g) + 3H_2(g) \rightleftharpoons 2NH_3(g)$ the reaction is exothermic
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(c) Another compound which contains only nitrogen and hydrogen is hydrazine, $N_2H_4$. Complete the equation for the preparation of hydrazine from ammonia.
....NH$_3$ + NaClO $\rightarrow$ $N_2H_4$ + ........... + $H_2O$ [2]
(d) The structural formula of hydrazine is given below.

Draw a diagram showing the arrangement of the valency electrons in one molecule of the covalent compound hydrazine.
Use x to represent an electron from a nitrogen atom.
Use o to represent an electron from a hydrogen atom.
[3]
(e) Hydrazine is a weak base and it removes dissolved oxygen from water. It is added to water in steel boilers to prevent rusting.
(i) One way it reduces the rate of rusting is by changing the pH of water. What effect would hydrazine have on the pH of water?
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(ii) Give a reason, other than pH, why hydrazine reduces the rate of rusting.
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(a) (i) Crystals of lithium chloride can be prepared from lithium hydroxide by titration. 25.0 cm$^3$ of aqueous lithium hydroxide is pipetted into the conical flask. A few drops of an indicator are added. Dilute hydrochloric acid is added slowly to the alkali until the indicator just changes colour. The volume of acid needed to neutralise the lithium hydroxide is noted. A neutral solution of lithium chloride, which still contains the indicator, is left. Describe how you could obtain a neutral solution of lithium chloride which does not contain an indicator. ................................................................................................................................................ ................................................................................................................................................ [2]
(ii) You cannot prepare a neutral solution of magnesium chloride by the same method. Describe how you could prepare a neutral solution of magnesium chloride. ................................................................................................................................................ ................................................................................................................................................ ................................................................................................................................................ [3]
(b) The concentration of the hydrochloric acid was 2.20 mol/dm$^3$. The volume of acid needed to neutralise the 25.0 cm$^3$ of lithium hydroxide was 20.0 cm$^3$. Calculate the concentration of the aqueous lithium hydroxide.
$LiOH + HCl \rightarrow LiCl + H_2O$ ................................................................................................................................................ ................................................................................................................................................ ................................................................................................................................................ [2]
(c) Lithium chloride forms three hydrates. They are $LiCl.H_2O$, $LiCl.2H_2O$ and $LiCl.3H_2O$. Which one of these three hydrates contains 45.9% of water? Show how you arrived at your answer. ................................................................................................................................................ ................................................................................................................................................ ................................................................................................................................................ [3]

There are three types of giant structure - ionic, metallic and giant covalent.
(a) In an ionic compound, the ions are held in a lattice by strong forces.
(i) Explain the term lattice.
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(ii) Explain how the ions are held together by strong forces.
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(b) Describe the bonding in a typical metal.
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(c) The electrical conductivities of the three types of giant structure are given in the following table.

| type of structure | conductivity of solid | conductivity of liquid |
|------------------|----------------------|----------------------|
| ionic | poor | good |
| metallic | good | good |
| giant covalent | poor | poor |

Explain the differences in electrical conductivity between the three types of giant structure and the difference, if any, between the solid and liquid states of the same structure.
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