Cambridge IGCSE Chemistry - 0620 - Supplement Paper 4 2010 Winter Zone 1

The table gives the composition of three particles.

[Table_1: particle | number of protons | number of electrons | number of neutrons
A | 15 | 15 | 16
B | 15 | 18 | 16
C | 15 | 15 | 17]

(a) What is the evidence in the table for each of the following?
(i) Particle A is an atom. ...................................................... [1]
(ii) They are all particles of the same element. ...................................................... [1]
(iii) Particle B is a negative ion. ...................................................... [2]
(iv) Particles A and C are isotopes. ...................................................... [2]

(b) (i) What is the electronic structure of particle A? ...................................................... [1]
(ii) What is the valency of the element? ...................................................... [1]
(iii) Is the element a metal or a non-metal? Give a reason for your choice. ...................................................... [1]

About 4000 years ago the Bronze Age started in Britain. Bronze is an alloy of copper and tin.
(a) (i) Suggest a reason why a bronze axe was better than a copper axe.
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(ii) Brass is another copper alloy. Name the other metal in brass.
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(b) The diagram below shows the arrangement of particles in a pure metal.

(i) What is the name given to a regular arrangement of particles in a crystalline solid?
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(ii) Draw a diagram which shows the arrangement of particles in an alloy.
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(iii) Explain the term malleable.
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(iv) Why are metals malleable?
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(c) The common ore of tin is tin(IV) oxide and an ore of copper is malachite, CuCO_3.Cu(OH)_2.
(i) Write a word equation for the reduction of tin(IV) oxide by carbon.
.............................................................................................................................................................................................. [1]
(ii) Malachite is heated to form copper oxide and two other chemicals. Name these chemicals.
................................................. and ............................... and ............................................................... [2]
(iii) Copper oxide is reduced to copper which is then refined by electrolysis. Label the diagram of the apparatus which could be used to refine copper.
[3]
(iv) Give one use of copper, other than making alloys.
.............................................................................................................................................................................................. [1]

The diagram shows a cell. This is a device which produces electrical energy. The reaction in a cell is a redox reaction and involves electron transfer.



(i) Complete the sentence.
A cell will change .............................................. energy into electrical energy. [1]

(ii) Draw an arrow on the diagram to show the direction of the electron flow. [1]

(iii) In the left hand beaker, the colour changes from brown to colourless. Complete the equation for the reaction.
$$ \text{Br}_2 + .............. \rightarrow .............. $$ [2]

(iv) Is the change in (iii) oxidation or reduction? Give a reason for your choice.
...........................................................................................................................
........................................................................................................................... [1]

(v) Complete the following description of the reaction in the right hand beaker.
Fe$^{2+}$ changes into .......................... . [1]

(vi) When a solution of bromine is replaced by a solution of chlorine, the voltage increases. When a solution of bromine is replaced by a solution of iodine, the voltage decreases. Suggest an explanation for this difference.
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.......................................................................................................................... [1]

Ammonia is an important industrial chemical.
(a) (i) Give the electron structure of an atom of nitrogen.
................................................................................................................................................ [1]
(ii) Use this electronic structure, rather than the valency of nitrogen, to explain why the formula of ammonia is NH$_3$ not NH$_4$.
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(b) Ammonia is made by the Haber Process.
$$N_2(g) + 3H_2(g) \leftrightarrow 2NH_3(g)$$ forward reaction is exothermic
The percentage of ammonia in the equilibrium mixture varies with conditions.

[Table_1]

pressure / atmospheres	100	200	300	400
% ammonia at 300°C	45	65	72	78
% ammonia at 500°C	9	18	25	31

The conditions actually used are 200 atmospheres, 450°C and an iron catalyst.
(i) The original catalyst was platinum. Suggest a reason why it was changed to iron.
................................................................................................................................................ [1]
(ii) Explain why the highest pressure gives the highest percentage of ammonia in the equilibrium mixture.
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(iii) What happens to the unreacted nitrogen and hydrogen?
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................................................................................................................................................ [1]
(iv) State one advantage and one disadvantage of using a lower temperature.
advantage ......................................................................................................................... [1]
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disadvantage ...................................................................................................................
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Monomers polymerise to form polymers or macromolecules.

(a) (i) Explain the term polymerise.
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(ii) There are two types of polymerisation - addition and condensation. What is the difference between them?
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(b) An important monomer is chloroethene which has the structural formula shown below.

It is made by the following method.
$C_2H_4 + Cl_2 \rightarrow C_2H_4Cl_2$ dichloroethane
This is heated to make chloroethene.
$C_2H_4Cl_2 \rightarrow C_2H_3Cl + HCl$

(i) Ethene is made by cracking alkanes. Complete the equation for cracking dodecane.
$C_{12}H_{26} \rightarrow .................... + 2C_2H_4$ [1]

Another method of making dichloroethane is from ethane.
$C_2H_6 + 2Cl_2 \rightarrow C_2H_4Cl_2 + 2HCl$

(ii) Suggest a reason why the method using ethene is preferred.
.......................................................................................................................................
....................................................................................................................................... [1]

(iii) Describe an industrial method of making chlorine.
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....................................................................................................................................... [2]

(iv) Draw the structural formula of poly(chloroethene).
Include three monomer units. [2]

The table below shows the elements in the second period of the Periodic Table and some of their oxidation states in their most common compounds.

[Table_1]

element	Li	Be	B	C	N	O	F	Ne
number of outer electrons	1	2	3	4	5	6	7	8
oxidation state	+1	+2	+3	+4	–3	–2	–1	0

(a) (i) What does it mean when the only oxidation state of an element is zero?
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.................................................................................................................. [1]

(ii) Explain why some elements have positive oxidation states but others have negative ones.
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(iii) Select two elements in the table which exist as diatomic molecules of the type $X_{2}$.
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(b) Beryllium hydroxide, a white solid, is an amphoteric hydroxide.

(i) Name another metal which has an amphoteric hydroxide.
.................................................................................................................. [1]

(ii) Suggest what you would observe when an excess of aqueous sodium hydroxide is added gradually to aqueous beryllium sulfate.
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.................................................................................................................. [2]

(c) (i) Give the formulae of lithium fluoride and nitrogen fluoride.
lithium fluoride ...................................................................................................
nitrogen fluoride .............................................................................................. [2]

(ii) Predict two differences in their properties.
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.................................................................................................................. [2]

(iii) Explain why these two fluorides have different properties.
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The diagram shows part of the carbon cycle. This includes some of the processes which determine the percentage of carbon dioxide in the atmosphere.
(i) Carbon dioxide is one greenhouse gas. Name another one. [1]
(ii) Explain the term respiration and how this process increases the percentage of carbon dioxide in the atmosphere. [3]
(iii) Explain why the combustion of waste crop material should not alter the percentage of carbon dioxide in the atmosphere. [2]
(iv) In 1960 the percentage of carbon dioxide in the atmosphere was 0.032% and in 2008 it was 0.038%. Suggest an explanation for this increase. [2]

(a) Complete this method of preparing dry crystals of the soluble salt cobalt(II) chloride-6-water from the insoluble base cobalt(II) carbonate.

Step 1
Add an excess of cobalt(II) carbonate to hot dilute hydrochloric acid.

Step 2
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Step 3
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Step 4
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(b) 6.0 g of cobalt(II) carbonate was added to 40 cm$^3$ of hydrochloric acid, concentration 2.0 mol/dm$^3$. Calculate the maximum yield of cobalt(II) chloride-6-water and show that the cobalt(II) carbonate was in excess.

$\text{CoCO}_3 + 2\text{HCl} \rightarrow \text{CoCl}_2 + \text{CO}_2 + \text{H}_2\text{O}$
$\text{CoCl}_2 + 6\text{H}_2\text{O} \rightarrow \text{CoCl}_2.6\text{H}_2\text{O}$

Maximum yield
Number of moles of HCl used = ...........................
Number of moles of CoCl$_2$ formed = ...........................
Number of moles of CoCl$_2$.6H$_2$O formed = ...........................
Mass of one mole of CoCl$_2$.6H$_2$O = 238 g
Maximum yield of CoCl$_2$.6H$_2$O = ........................... g [4]

To show that cobalt(II) carbonate is in excess
Number of moles of HCl used = ........................... (use value from above)
Mass of one mole of CoCO$_3$ = 119 g
Number of moles of CoCO$_3$ in 6.0 g of cobalt(II) carbonate = ........................... [1]
Explain why cobalt(II) carbonate is in excess .......................................................... [1]