IGCSEChemistry: Co-ordinated Sciences (Double Award)CIETopic QuestionsChemical ReactionsRedox

Redox (CIE IGCSE Chemistry: Co-ordinated Sciences (Double Award))

Topic Questions

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1a2 marks

This question is about the reactions of metals with oxygen.

Complete the sentences.

In terms of oxygen, ____________________ is the loss of oxygen.

In terms of oxygen, ____________________ is the gain of oxygen.

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1b2 marks

Iron can react with oxygen to form iron(II) oxide.

2Fe + O2 → 2FeO

Iron can also react with oxygen to form iron(III) oxide

4Fe + 3O2 → 2Fe2O3 

Nickel can react with oxygen to form nickel(II) oxide or nickel(III) oxide.

Write two balanced symbol equations to show both reactions of nickel with oxygen.

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1c2 marks

Nickel is below carbon in the reactivity series.

This means that carbon can be used to extract nickel from nickel(II) oxide. 

nickel(II) oxide + carbon → nickel + carbon dioxide

The reaction of nickel(II) oxide with carbon is a redox reaction.

Is carbon oxidised or reduced? Explain your answer. 

 
Carbon is ____________________
 
Reason: ____________________

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1d2 marks

Extended tier only

Nickel can also be extracted from nickel(III) oxide using carbon.

Nickel(III) gains electrons to form nickel.

Balance the half-equation to show how nickel gains electrons:

Ni3+      +     .... e–     →    .........  

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2a1 mark

Extended tier only

During metal displacement reactions, the metal that is the least reactive metal is reduced.

Which of these statements correctly describes what reduction is?

Tick one box.

The gain of oxygen  
   
The gain of electrons  
   
The simulatanous gain and loss of electrons  
   
An increase in oxidation number  

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2b1 mark

Which of the following reactions shows iron being reduced? 
Tick one box.

copper nitrate + iron → iron nitrate + copper  
   
iron + oxygen → iron(II) oxide  
   
iron(II) oxide + carbon → iron + carbon dioxide  
   
hydrochloric acid + iron → iron chloride + hydrogen  

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3a1 mark

The reaction of zinc oxide with carbon is an example of a redox reaction.

What is meant by the term redox reaction?

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3b1 mark

When zinc oxide reacts with carbon, carbon displaces zinc from its oxide.

ZnO + C → Zn + CO

How does this equation show that zinc oxide is reduced?

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3c1 mark

Iron oxide can also be reduced by carbon.
Iron oxide can exist as iron(II) oxide or iron(III) oxide.

What do the Roman numerals indicate in the names of the compound?

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3d2 marks

Complete the balanced equation to show the reduction of iron(III) oxide with carbon.

2Fe2O3 + .... C → .... Fe + .... CO2

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4a1 mark

Extended tier only

Chromium(II) oxide can be formed from the reaction between chromium and oxygen.

Complete the half-equation for the reaction.

.........  →  Cr2+  +  ..... e–

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4b1 mark

Extended tier only

The other half-equation for the reaction is shown below.

O2 + 4e– → 2O2–

Explain, in terms of electrons, how this shows that oxygen has been reduced.

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1a1 mark

Which metals in the series above do not react with dilute acids to form hydrogen?

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1b1 mark

Describe an experiment which would confirm the prediction made in (a).

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2a5 marks

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.

cie-igcse-sq-6-3-q4a
i)
What does it mean when the only oxidation state of an element is zero?

[1]

ii)
Explain why some elements have positive oxidation states but others have negative ones.

[2]

iii)
Select two elements in the table which exist as diatomic molecules of the type X2.

[2]

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2b6 marks
i)
Give the formulae of lithium fluoride and nitrogen fluoride.
 
Lithium fluoride ...................................................................................................
Nitrogen fluoride ..................................................................................................
[2]
ii)
Predict two differences in their properties.
[2]
iii)
Explain why these two fluorides have different properties.
[2]

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3a1 mark

When the oxide, Co3O4  is heated in hydrogen, cobalt metal is formed.


Co3O4   +  4H2   →   3Co   +   4H2O


Explain how this equation shows that Co3O4 is reduced.

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3b1 mark

The reaction of iron with steam is shown.

3Fe + 4H2O → Fe3O4 + 4H2

How does this equation show that iron gets oxidised?

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4a2 marks

Ammonia is manufactured by the Haber process.

Ammonia, NH3, is used to produce nitric acid, HNO3. This happens in a three-stage process.

Stage 1 is a redox reaction.

4NH3 + 5O2 → 4NO + 6H2O

Identify what is oxidised in stage 1.

Give a reason for your answer.

substance oxidised .....................................

reason    .....................................

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4b2 marks

Zinc and copper are elements next to each other in the Periodic Table.


Aqueous potassium iodide reacts with aqueous copper(II) sulfate to produce iodine.


Balance the chemical equation for this reaction.

KI space plus space CuSO subscript 4 space rightwards arrow space CuI space plus space straight I subscript 2 space plus space straight K subscript 2 SO subscript 4

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4c1 mark

Extended tier only

Deduce the charge on the copper ion in CuI.

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4d1 mark

Extended tier only

In terms of electron transfer, explain why copper is reduced in this reaction.

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12 marks

Vanadium is a transition element. It has more than one oxidation state.
The element and its compounds are often used as catalysts.

Predict three physical properties of vanadium which are typical of transition elements.

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2a5 marks

The following are examples of redox reactions.

Bromine water was added to aqueous sodium sulfide. The ionic equation is:

Br2 (aq) + S2– (aq) → 2Br– (aq) + S(s)

i)
Describe what you would observe when this reaction occurs.

[2]

ii)
Write a full symbol equation for this reaction.

[1]

iii)
Explain, in terms of electron transfer, why bromine is the oxidant (oxidising agent) in this reaction.

[2]

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2b8 marks

Extended tier only

Iron and steel in the presence of water and oxygen form rust.

cie-igcse-sq-6-3-rusting-diagram-

The reactions involved are:
reaction 1

Fe → Fe2+ + 2e–

The electrons move through the iron onto the surface where a colourless gas forms.

reaction 2

Fe2+ + 2OH– → Fe(OH)2

reaction 3

..........Fe(OH)2 + O2 + ..........H2O → ..........Fe(OH)3

The water evaporates to leave rust.

i)
What type of reaction is reaction 1?

[1]

ii)
Deduce the name of the colourless gas mentioned in reaction 1.

[1]

iii)
What is the name of the iron compound formed in reaction 2?

[1]

iv)
Balance the equation for reaction 3.
..........Fe(OH)2 + O2 + ..........H2O → ..........Fe(OH)3

[1]

v)
Explain why the change Fe(OH)2 to Fe(OH)3 is oxidation.

[1]

vi)
Explain why iron in electrical contact with a piece of zinc does not rust.

[3]

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3a2 marks

The distinctive smell of the seaside was thought to be caused by ozone, O3.
Ozone is a form of the element oxygen.

A mixture of oxygen and ozone is formed by passing electric sparks through oxygen.

3O2 rightwards harpoon over leftwards harpoon2O3

Suggest a technique that might separate this mixture. Explain why this method separates the two forms of oxygen.

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3b4 marks

Extended tier only

Ozone is an oxidant. It can oxidise an iodide ion to iodine.

2I– + O3 + 2H+ → I2 + O2 + H2O

i)
What would you see when ozone is bubbled through aqueous acidified potassium iodide?

[2]

ii)
Explain in terms of electron transfer why the change from iodide ions to iodine molecules is oxidation.

[1]

iii)
Explain, using your answer to b(ii), why ozone is the oxidising agent in this reaction.

[1]

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3c5 marks

Extended tier only

It is now known that the smell of the seaside is due to the chemical dimethyl sulfide, (CH3)2S.

i)
Draw a diagram that shows the arrangement of the outer electrons in one molecule of this covalent compound.
Use x to represent an electron from a carbon atom.
Use ● to represent an electron from a hydrogen atom.
Use o to represent an electron from a sulfur atom.

[3]

ii)
Name the three compounds formed when dimethyl sulfide is burnt in excess oxygen.

[2]

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4a2 marks

An ore of tungsten conatins WO3. Tungsten can be obtained from WO3 by reacting it with hydrogen. The reaction is a redox reaction, water is also produced.

Write the balanced symbol equation for the reaction.

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4b2 marks

Extended tier only

Explain reduction and oxidation in terms of electrons and oxidation numbers.

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4c
Sme Calculator5 marks

Extended tier only

50 tonnes of the tungsten ore were processed. The ore was found to contain 3.4% of WO3 by mass.

Calculate the maximum mass, in tonnes, of tungsten that could be obtained from this ore.

Give your answer to three significant figures.

[Ar (W) = 184;    Mr (WO3) = 232]

maximum mass of tungsten = ................................................. tonnes

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