Cambridge IGCSE Chemistry - 0620 - Supplement Paper 4 2014 Summer Zone 1

The table below gives the composition of six particles which are either atoms or ions.

[Table_1]

(a) Which particles are atoms? Explain your choice.
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(b) Which particle is a negative ion and why has this particle got a negative charge?
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(c) Which particles are positive ions?
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(d) Explain why particle A and particle D are isotopes.
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(a) Water is needed for industry and in the home.

(i) Rain water is collected in reservoirs. How is it treated before entering the water supply?
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(ii) State \textbf{two} industrial uses of water.
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(iii) State \textbf{two} uses of water in the home.
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(b) In many regions, drinking water is obtained by the distillation of sea-water. Explain how distillation separates the water from sea-water.
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(a) Different gases diffuse at different speeds.

(i) What is meant by the term \textit{diffusion}?
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(ii) What property of a gas molecule affects the speed at which it diffuses?
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(b) Helium is a gas used to fill balloons. It is present in the air in very small quantities. Diffusion can be used to separate it from the air.

Air at 1000°C is on one side of a porous barrier. The air which passes through the barrier has a larger amount of helium in it.

(i) Why does the air on the other side of the barrier contain more helium?
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(ii) Why is it an advantage to have the air at a high temperature?
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(c) Most helium is obtained from natural gas found in the USA. Natural gas contains methane and 7% helium. One possible way to obtain the helium would be to burn the methane.

(i) Write an equation for the complete combustion of methane.
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(ii) Suggest why this would \textbf{not} be a suitable method to obtain the helium.
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(iii) Suggest another method, other than diffusion, by which helium could be separated from the mixture of gases in natural gas.
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In the Periodic Table, the elements are arranged in columns called Groups and in rows called Periods.
(a) (i) Complete the table for some of the elements in Period 3.

[Table_1]

| group number | I | II | III | IV | V | VI | VII |
|--------------|----|-----|-----|----|----|----|-----|
| symbol | Na | Mg | Al | Si | P | S | Cl |
| number of valency electrons | | | | | | | |
| valency | | | | | | | |

[2]

(ii) What is the relationship between the group number and the number of valency electrons?
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[1]

(iii) Explain the relationship between the number of valency electrons and the valency
for the elements Na to Al,
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for the elements P to Cl.
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(b) Across a period, the elements change from metallic to non-metallic.
(i) Describe how the type of oxide changes across this period.
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[2]

(ii) Describe how the type of bonding in the chlorides formed by these elements changes across this period.
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[2]

Zinc is obtained from the ore, zinc blende, ZnS.

(a) Describe the extraction of zinc from its ore, zinc blende. Include at least one balanced equation in your description.
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(b) State two major uses of zinc.
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Hydrogen peroxide decomposes to form water and oxygen. This reaction is catalysed by manganese(IV) oxide.
$$2H_2O_2(aq) \rightarrow 2H_2O(l) + O_2(g)$$
The rate of this reaction can be investigated using the following apparatus.

40 cm³ of aqueous hydrogen peroxide was put in the flask and 0.1 g of small lumps of manganese(IV) oxide was added. The volume of oxygen collected was measured every 30 seconds. The results were plotted to give the graph shown below.

(a) (i) How do the rates at times $t_1$, $t_2$ and $t_3$ differ?
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(ii) Explain the trend in reaction rate that you described in (a)(i).
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(b) The experiment was repeated using 0.1 g of finely powdered manganese(IV) oxide. All the other variables were kept the same.
(i) On the axes opposite, sketch the graph that would be expected. [2]
(ii) Explain the shape of this graph. ..........................................................................................
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(c) Describe how you could show that the catalyst, manganese(IV) oxide, was not used up in the reaction. Manganese(IV) oxide is insoluble in water.
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(d) In the first experiment, the maximum volume of oxygen produced was 96 cm³ measured at r.t.p. Calculate the concentration of the aqueous hydrogen peroxide in mol/dm³.
$$2H_2O_2(aq) \rightarrow 2H_2O(l) + O_2(g)$$
number of moles of $O_2$ formed = ..........................................................
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number of moles of $H_2O_2$ in 40 cm³ of solution = ...........................
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concentration of the aqueous hydrogen peroxide in mol/dm³ = ..........................
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(a) A series of experiments was carried out using the metals lead, magnesium, zinc and silver. Each metal was added in turn to aqueous solutions of the metal nitrates.

The order of reactivity was found to be:

magnesium most reactive
zinc
lead
silver least reactive

(i) Complete the table.
✓ = reacts
✗ = does not react



(ii) Displacement reactions are redox reactions. On the following equation, draw a ring around the reducing agent and an arrow to show the change which is oxidation.

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

(iii) Complete the following ionic equation.

$Zn + 2Ag^{+} \rightarrow \ldots\ldots + \ldots\ldots$

(b) Another way of determining the order of reactivity of metals is by measuring the voltage and polarity of simple cells. The polarity of a cell is shown by which metal is the positive electrode and which metal is the negative electrode. An example of a simple cell is shown below.



(i) Mark on the above diagram the direction of the electron flow.

(ii) Explain, in terms of electron transfer, why the more reactive metal is always the negative electrode.

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(iii) The following table gives the polarity of cells using the metals zinc, lead, copper and manganese.

[Table_1]

What information about the order of reactivity of these four metals can be deduced from the table?

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(iv) What additional information is needed to establish the order of reactivity of these four metals using cells?

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Polymers are made by the polymerisation of simple molecules called monomers.

(a) (i) The structural formula of a polymer is given below.



This polymer is made by addition polymerisation. Draw the structural formula of its monomer. [1]

(ii) The two monomers shown below form a nylon which is a condensation polymer.



Draw its structural formula showing one repeat unit of the polymer. [3]

(iii) Name the natural macromolecule which contains the same linkage as nylon.
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(iv) Explain the difference between addition polymerisation and condensation polymerisation.
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(b) Many polymers are non-biodegradable.

(i) Explain the term non-biodegradable.
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(ii) State three problems caused by the disposal of non-biodegradable polymers.
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(c) Storage tanks for cold water are now made from polymers because they are cheaper than metal tanks. Suggest two other advantages of making cold water tanks from polymers.
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