Cambridge IGCSE Chemistry - 0620 - Core Paper 3 2017 Summer Zone 3

(a) The electronic structures of five atoms, A, B, C, D, and E, are shown.

Answer the following questions about these atoms.
Each atom may be used once, more than once, or not at all.
Which atom, A, B, C, D, or E,
(i) is in Group VIII of the Periodic Table, ................................. [1]
(ii) is a chlorine atom, ................................. [1]
(iii) has 17 protons in its nucleus, ................................. [1]
(iv) is an atom of an element in the same period as carbon, ................................. [1]
(v) is an atom of a metal? ................................. [1]
(b) Complete the table to show the number of electrons, neutrons, and protons in the magnesium atom and calcium ion shown.
[Table_1]
\( \begin{array}{ccc} \text{number of electrons} & \text{number of neutrons} & \text{number of protons} \\ \frac{26}{12} \text{Mg} & 12 & \\ \frac{44}{20} \text{Ca}^{2+} & 24 & \\ \end{array} \) [3]

(a) The table shows the ions present in a 1000 cm³ sample of mineral water.

Answer these questions using the information from the table.
(i) Calculate the mass of magnesium ions in the 1000 cm³ sample of mineral water.
mass of magnesium ions = ................................ mg [1]
(ii) Which negative ion is present in the highest concentration?
................................................................................................................................ [1]
(iii) State the name of the ion NO₃^-.
................................................................................................................................ [1]
(iv) Calculate the mass of hydrogencarbonate ions present in 250 cm³ of this sample.
mass of hydrogencarbonate ions = ................................ mg [1]

(b) When nitrate ions are warmed with aqueous sodium hydroxide and aluminium foil, ammonia gas is given off.
Describe a test for ammonia gas.
test ..................................................................................................................
result .................................................................................................................. [2]

(c) The formulae of some bromides are given.
aluminium bromide, AlBr₃
magnesium bromide, MgBr₂
sodium bromide, NaBr
Deduce the formula for calcium bromide.
.................................................................................................................. [1]

(d) Molten calcium bromide can be electrolysed using inert electrodes.
(i) Predict the products of this electrolysis at
the negative electrode (cathode), ...................................................
the positive electrode (anode). .................................................. [2]
(ii) Graphite electrodes are inert.
Give the name of one other substance that can be used to make an inert electrode.
.................................................................................................................. [1]

The diagram shows part of the structures of three substances, P, Q and R, at room temperature and pressure.
(a) Describe substances P, Q and R in terms of
• their bonding,
• the arrangement of their particles,
• the motion of their particles.
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(b) A closed gas syringe contains substance R. The syringe is heated in a water bath.
Describe what happens to the volume of substance R in the syringe. The pressure remains constant. Explain your answer in terms of particles.
....................................................................................................................................................
.................................................................................................................................................... [2]
(c) Substance P undergoes physical and chemical changes.
Which two of the following are physical changes? Explain your answer.
A Substance P reacts with concentrated sulfuric acid.
B Iodine forms when chlorine is added to an aqueous solution of substance P.
C Substance P boils at 1330 °C.
D Substance P dissolves easily in water.
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....................................................................................................................................................
.................................................................................................................................................... [3]
(d) Graphite has a giant covalent structure containing layers of carbon atoms. Graphite is used to make inert electrodes for electrolysis.
State one other use of graphite and explain how this use is related to its structure.
....................................................................................................................................................
.................................................................................................................................................... [2]

Iron is extracted from its ore by heating the ore with carbon in a blast furnace.
(a) (i) State the name of an ore of iron.
............................................................................................................................. [1]
(ii) In the blast furnace, iron(III) oxide is reduced by carbon monoxide. Explain how the carbon monoxide is formed in the blast furnace.
.............................................................................................................................
............................................................................................................................. [2]
(iii) Balance the chemical equation for this reaction.
$$ \text{Fe}_2\text{O}_3 + 3\text{CO} \rightarrow ......\text{Fe} + ......\text{CO}_2 $$ [2]
(iv) How does this equation show that iron(III) oxide is reduced?
............................................................................................................................. [1]
(v) Calculate the relative formula mass of iron(III) oxide, Fe₂O₃. Show all your working. Use your Periodic Table to help you.
Relative formula mass = ............................. [2]
(b) Iron reacts with hydrochloric acid to form iron(II) chloride and a gas which ‘pops’ with a lighted splint.
(i) Identify this gas.
............................................................................................................................. [1]
(ii) Suggest a practical method for investigating the rate of this reaction involving collection of the gas. You may include a labelled diagram in your answer.
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............................................................................................................................. [3]
(c) Describe a test for iron(II) ions.
test .............................................................................................................................
result ............................................................................................................................. [2]
(d) Give two advantages of recycling steel.
1 .............................................................................................................................
2 ............................................................................................................................. [2]

Glycolic acid is found in the stalks of sugar-cane plants.
The structure of glycolic acid is shown.

(a) On the structure shown draw a circle around the carboxylic acid functional group. [1]
(b) Give the molecular formula of glycolic acid showing the number of carbon, hydrogen and oxygen atoms. [1]
..........................................................................................................................
(c) Suggest how you could obtain a solution containing glycolic acid from sugar-cane plants. [3]
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(d) Nitric acid can oxidise glycolic acid.
What is the meaning of the term oxidation? [1]
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(e) The table shows the properties of some carboxylic acids.
[Table_1]
(i) Describe how the density of the carboxylic acids varies with the number of carbon atoms in one molecule. [1]
..........................................................................................................................
(ii) Predict the boiling point of propanoic acid. [1]
..........................................................................................................................
(iii) What is the state of butanoic acid at -10°C? Explain your answer. [2]
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(a) The table shows the properties of some alloys.

[Table_1]

Use the information in the table to answer the questions.

(i) Which alloy would be most useful for making a bridge? Give two reasons for your answer.
alloy ................
reason 1 .........................................................................................................
reason 2 .........................................................................................................
[2]

(ii) Which alloy is best to make the tips of high-speed drills? Give one reason for your answer.
alloy ................
reason ............................................................................................................
[1]

(iii) Which alloy is best to make aircraft bodies? Give one reason for your answer.
alloy ................
reason...............................................................................................................
[1]

(b) A student took pieces of four different steel alloys, W, X, Y and Z, each of the same mass, and placed them separately into hydrochloric acid. The concentration of acid was the same in each case and the metal was in excess. All other conditions were kept the same.

The student measured the mass of each alloy at intervals as the reaction proceeded and calculated the percentage mass loss.

The results for alloys W, X and Y are shown on the graph.

[Graph_1]

(i) Alloy Z reacts faster with hydrochloric acid than alloy W.
On the graph, draw a line which could represent the percentage mass loss of alloy Z with time.
[2]

(ii) Which alloy showed the least percentage mass loss after 3 days?
............................................................................................................................
[1]

(iii) How long did it take for alloy X to lose 40% of its mass?
............................................................................................................................
[1]

(iv) Suggest how the following factors affect the rate of mass loss.
- increasing the temperature ....................................................................
- increasing the concentration of the acid ...............................................
[2]

(c) The concentration of an acid can be found by titrating it with aqueous sodium hydroxide.

Suggest which one of these pH values is the pH of concentrated aqueous sodium hydroxide. Draw a circle around the correct answer.

pH 1 pH 3 pH 7 pH 12
[1]

Water is a simple covalent compound.
(a) Complete the diagram to show the electrons in the covalent bonds in a water molecule.

[1]
(b) Give \textit{two} physical properties which distinguish a simple covalent compound from an ionic compound.
1 ..............................................................
2 ..............................................................
[2]
(c) Some information about the reaction of four metals with water is given.
cerium: reacts slowly with cold water
iron: reacts with steam only when extremely hot
lithium: reacts rapidly with cold water
magnesium: reacts slowly with hot water
List these metals in order of their reactivity. Put the least reactive metal first.
least reactive -----------------------------------------> most reactive
...........................................................................................
[2]
(d) (i) State the conditions needed for iron to rust.
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[2]
(ii) State two methods of rust prevention.
1 ..............................................................
2 ..............................................................
[2]
(e) Starting with an aqueous solution of copper(II) sulfate, describe how you could obtain a pure dry sample of copper(II) sulfate crystals.
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[2]
(f) Carbon dioxide and water are formed when hydrocarbons burn.
Complete the chemical equation for the combustion of butene.
$$C_4H_8 + 6O_2 \rightarrow ......CO_2 + ......H_2O$$
[2]