Cambridge IGCSE Chemistry - 0620 - Core Paper 3 2016 Winter Zone 2

The diagram shows part of the Periodic Table.



Answer the following questions using only the elements in the diagram. Each element may be used once, more than once or not at all.

(a) Which element

(i) gives a lilac colour in a flame test,
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(ii) is a pinkish-brown metal,
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(iii) can exist in at least two different solid forms,
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(iv) has a full outer electron shell containing two electrons,
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(v) is extracted from hematite?
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(b) Silver has two naturally occurring isotopes.

$$^{107}_{47}\text{Ag} \text{ and } ^{109}_{47}\text{Ag}$$

Complete the table to show the number of protons, electrons and neutrons in these two isotopes.

[Table_1]

$$\begin{array}{|c|c|c|} \hline & ^{107}_{47}\text{Ag} & ^{109}_{47}\text{Ag} \\ \hline \text{number of protons} & & \\ \hline \text{number of electrons} & & \\ \hline \text{number of neutrons} & & \\ \hline \end{array}$$ [3]

The bar charts compare the concentrations of ions in two samples of water, sample A and sample B.

(a) Use the information in the bar charts to answer the following questions.
(i) Describe two differences in the composition of sample A and sample B.
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(ii) Which positive ion has the lowest concentration in sample B?
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(iii) Calculate the mass of chloride ions present in 100 cm³ of sample B. Show all your working. [1 dm³ = 1000 cm³]
mass = ..................... mg [2]
(b) Describe a test for chloride ions.
test .....................................................................................................................................................
result ................................................................................................................................................... [2]

(c) River water contains small particles of clay. These particles show Brownian motion.
Which one of these statements best describes Brownian motion? Tick one box.
☐ the diffusion of gases
☐ the random movement of particles in a suspension
☐ the downward movement of particles in a suspension [1]

(d) Silicon in river water comes from silicate rocks. Some of these contain silicon(IV) oxide.
Explain why silicon(IV) oxide is an acidic oxide.
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(e) River water contains dissolved oxygen. The graph shows how the concentration of dissolved oxygen changes with temperature.

(i) Describe how the concentration of dissolved oxygen changes with temperature.
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(ii) Determine the concentration of oxygen present in the water at 10°C.
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(iii) Suggest how the rate of corrosion of iron water pipes changes with temperature. Explain your answer.
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(f) Describe how water is treated to make it suitable to drink.
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(g) Oxides of nitrogen are common pollutants in the air.
(i) State one source of oxides of nitrogen in the air.
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(ii) State one adverse effect of oxides of nitrogen on health.
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Iron is a metal.

(a) The equation for the reaction of iron with steam is shown.
$$3\text{Fe} + 4\text{H}_2\text{O} \rightarrow \text{Fe}_3\text{O}_4 + 4\text{H}_2$$
Which substance is reduced in this reaction?
Explain your answer.
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(b) Iron is extracted by heating iron ore with carbon in a blast furnace.

(i) What is the meaning of the term ore?
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(ii) Air is blown into the blast furnace.
What is the purpose of this air?
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(iii) The impurities in the iron ore are removed as slag.
Which one of the following is slag?
Tick one box.
- iron(II) oxide [ ]
- calcium silicate [ ]
- calcium carbonate [ ]
- coke [ ] [1]

(iv) Slag is less dense than iron.
The diagram shows a blast furnace used to extract iron.
On the diagram, write the letter S to show where the slag is removed.
[1]

(c) Iron from the blast furnace contains impurities.
The diagram shows a converter used to make steel from iron.

Describe how iron is converted into steel.
In your answer
• describe the impurities present,
• describe how the impurities are removed,
• include a relevant word equation.
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Methyl orange and methyl red are both dyes which can be used as indicators.

(a) The actual value for the melting point of methyl red is 180°C.
A chemist prepares a sample of methyl red and finds that it melts over the range 173°C to 177°C.

Suggest why the melting point of this sample was different from the actual value.
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(b) A concentrated solution of methyl orange was placed at the bottom of a beaker containing an organic solvent.
After 5 hours, the orange colour had spread throughout the solvent.



Use the kinetic particle model of matter to explain this observation.
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(c) Methyl orange is used as an indicator.

What colour is methyl orange when placed in dilute sulfuric acid?
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(d) Sulfuric acid can be used to prepare copper(II) sulfate from copper(II) oxide.

(i) Complete the general word equation for this reaction.
metal oxide + acid → .......................... + ..........................
[2]

(ii) Sulfuric acid is added to excess copper(II) oxide. The mixture is heated and the unreacted copper(II) oxide is removed.

Suggest how the unreacted copper(II) oxide is removed.
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(iii) Put statements A to E about the preparation of pure dry crystals of copper(II) sulfate from copper(II) sulfate solution in the correct order.

A The crystals are filtered off.
B The heating is stopped when the point of crystallisation is reached.
C The mixture is left to form crystals.
D The crystals are dried with filter paper.
E The solution is heated gently.

correct order [2]

Cement is made by heating clay with limestone. Some of the limestone (calcium carbonate) breaks down to form calcium oxide and a gas which turns limewater milky.

(a) (i) Complete the chemical equation for this reaction.

$$ ext{CaCO}_3 ightarrow ext{..............} + ext{..............}$$ [2]

(ii) What type of chemical reaction is this?

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(iii) Determine the relative formula mass of calcium carbonate. Show all your working.

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(b) Concrete is a mixture of cement, sand, water and small stones.

Calcium carbonate is a compound, but concrete is a mixture.

State two differences between a compound and a mixture.

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(c) Reinforced concrete contains steel bars within the concrete.



Some properties of concrete and steel are shown in the table.

[Table_1]

Use the information in the table to suggest why concrete must be reinforced with steel when it is used to make bridges.

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(d) If reinforced concrete becomes cracked, liquids and gases can reach the steel bars. The steel bars rust.

Which two substances are needed for steel to rust?

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Petroleum can be separated into useful hydrocarbon fractions by fractional distillation.
(a) (i) Explain the term hydrocarbon fraction.
hydrocarbon ....................................................
fraction ...............................................................
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[2]
(ii) State one use for each of the following hydrocarbon fractions.
naphtha .......................................................
kerosene ...................................................
[2]
(b) Organic compounds can be grouped into different homologous series.
Explain the term homologous series by referring to alkenes.
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[4]

(c) The table shows some information about alkenes.
[Table_1]
(i) A student predicts that the density of the liquid alkenes increases as the number of carbon atoms increases.
Describe whether the data in the table support this prediction.
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[1]
(ii) Predict the boiling point of hexene.
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[1]
(iii) Deduce the state of pentene at $-60^\circ\text{C}$. Explain your answer.
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[2]

(d) Draw the structure of ethene. Show all of the atoms and all of the bonds.

(e) Alkenes are manufactured by cracking.
When tetradecane, $C_{14}H_{30}$, is cracked the products are ethene, an alkene with four carbon atoms and an alkane.
Complete the chemical equation for this reaction.
$C_{14}H_{30} \rightarrow C_{2}H_{4} + .............. + ..............$
[2]

The graph shows how the temperature of sodium changes when it is heated at a constant rate in an atmosphere of argon.
(a) Suggest why the sodium is heated in argon and not in air.
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(b) Which part of the graph above represents the boiling point of sodium? Tick one box.
A–B □
B–C □
C–D □
D–E □
[1]
(c) (i) Describe two differences in the general properties of a liquid and a gas.
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(ii) Describe the arrangement and motion of the particles in a liquid.
Arrangement ................................................................................................................................
Motion ........................................................................................................................................ [2]
(d) Niobium is a transition element. Sodium is an element in Group I of the Periodic Table.
(i) Describe two properties of niobium which are different from sodium.
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(ii) The structure of niobium chloride is shown.
Determine the formula of niobium chloride.
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(iii) Niobium chloride is a covalent molecule.
Predict two physical properties of niobium chloride.
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