Electrochemistry and Oxidation and Reduction

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[email protected] Form 4 Chapter 6 and form 5 Chapter 3

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F4 Chapter 6 ElectrochemistryF5 Chapter 3 Oxidation & Reduction

ANALYSIS OF PAST YEAR QUESTIONS FROM 2003 – 2008

Year 2003 2004 2005 2006 2007 2008

Paper No. P2 P3 P2 P3 P2 P3 P2 P3 P2 P3 P2 P3

Type of

questionS E S E S E S E S E S E S E S E S E S E S E S E

Question No

F4 Chp

6

F5 Chp

3

5 3 3 4 2 6 9 2

10

7 6 2

8

9

STRUCTURED QUESTIONS

1 SPM 2003/P2/Q5 Figure 5 shows the set-up of apparatus to investigate the reactions that take place intest tubes P and Q.

Figure 5

(a) State the observation for the reaction(i) in test tube P.

…………………………………………………………………………………

[1 mark ](ii) in test tube Q.

………………………………………………………………………………… [1 mark ]

(b) Write the ionic equation for the reaction in (a)(i).

……………………………………………………………………………………….. [1 mark ]

(c) State what is meant by oxidizing agent in terms of electron transfer.

………………………………………………………………………………………..

[1 mark ](d) Referring to the reaction that takes place in test tube P,




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(i) what is the change in the oxidation number of magnesium?

………………………………………………………………………………… [1 mark ]

(ii) name the oxidizing agent.

………………………………………………………………………………… [1 mark ]

(e) Referring to the reaction that takes place in test tube Q,(i) state the type of reaction that occurs.

………………………………………………………………………………… [1 mark ]

(ii) state the oxidation number of bromine in bromine water.

…………………………………………………………………………………

[1 mark ](iii) what is the function of bromine water?

………………………………………………………………………………… [1 mark ]

(iv) name another reagent that can replace bromine water.

………………………………………………………………………………… [1 mark ]

2 SPM 2004/P2/Q3

Figure 3 shows the set-up of apparatus to investigate the electrolysis of dilute

copper(II) sulphate solution.

Figure 3

(a) (i) What is meant by cation?

……………………………………………………………………………….... [1 mark ]

(ii) What is the energy change that occurs in the electrolysis process?

…………………………………………………………………………………




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[1 mark ](b) In the electrolysis of dilute copper(II) sulphate solution:

(i) State all the ions in the electrolyte.

…………………………………………………………………………………

[1 mark ]

(ii) In the table below, write the ions in (b)(i) which moved to electrodes X andY.

Electrode X Electrode Y

[1 mark ](iii) What are the processes that occur at electrodes X and Y?

Electrode X : …………………………………………………………………

Electrode Y : ………………………………………………………………… [1 mark ]

(iv) What would you observe at electrode Y?

………………………………………………………………………………… [1 mark ]

(v) What is the colour change of the electrolyte?

………………………………………………………………………………… [1 mark ]

(c) (i) Name the gas collected in the test tube at electrode X.

………………………………………………………………………………… [1 mark ]

(ii) The volume of gas collected at electrode X is 20.0 cm

3

.How many moles of the gas were collected?Use the information that 1 mole of gas occupies a volume of 24.0 dm3 atroom temperature and pressure.

[1 mark ]




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(iii) Based on the answer in (c)(ii), what is the number of gas moleculescollected?Use the information that the Avogadro number is 6.02 x 1023 mol-1.

[1 mark ]

3 SPM 2005/P2/Q6

Table 6 shows the descriptions and observations for two experiments, I and II.

Experiment Description Observation

I Electrolysis of 1 moldm-3 sodiumsulphate solutionusing carbonelectrodes.

Gas bubbles arereleased at theanode and cathode.

II Combustion of 1.2gof magnesiumpowder in excessoxygen.

Glaring white flameis seen and whitepowder is formed.

(a) Based on Experiment I:(i) Draw the set up of the apparatus to carry out this experiment. In your

diagram show how the products at the anode and cathode are collected.

[3 marks]




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(ii) State how you would verify that the gas released at the cathode ishydrogen.

………………………………………………………………………………

……………………………………………………………………………… [1 mark ]

(iii) Explain how hydrogen gas is produced at the cathode.

………………………………………………………………………………..

………………………………………………………………………………..

………………………………………………………………………………..

……………………………………………………………………………….. [3 marks]

(b) Based on Experiment II:(i) The white powder formed is magnesium oxide.

Write the formula for magnesium oxide.

…………………………………………………………………………………

[1 mark ](ii) Write the chemical equation for the reaction that takes place.

………………………………………………………………………………… [1 mark ]

(iii) State the oxidation number for each of the elements in magnesium oxide.

…………………………………………………………………………………

………………………………………………………………………………… [2 marks]

4 SPM 2007/P2/Q6 Iron is a metal that rusts easily.(a) (i) State the conditions for the rusting of iron.

………………………………………………………………………………… [1mark ]

(ii) Draw a labelled diagram to show how the conditions for the rusting of ironinvolve in the ionization of iron and the flow of electron.




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[3 marks](b) (i) Describe the reactions that take place at the edge of water droplet (positive

terminal) during the rusting of iron after the Fe

2+

and OH

-

ions are formed.

…………………………………………………………………………………

…………………………………………………………………………………

…………………………………………………………………………………

………………………………………………………………………………… [3 marks]

(ii) State the change in the oxidation number of iron in 6(b)(i).

………………………………………………………………………………… [ 1 mark ]

(c) Diagram 6 shows the use of zinc plates on an iron ship to prevent rusting.

Diagram 6(i) Explain how the zinc plates protect the iron ship from rusting.

…………………………………………………………………………………

………………………………………………………………………………… [2 marks]

(ii) Write the half equation for the rection in 6(c)(i).

………………………………………………………………………………… [1 mark ]

5 SPM 2004/P3/Q2

Metals are arranged in the Reactivity Series based on the reactivity of metalwith oxygen.

Figure 2.1 shows the set-up of apparatus for an experiment to determine the order ofmetals in the Reactivity Series.




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Potassium manganate(VII) is heated to release oxygen gas to react with metal powder.

Figure 2.1The experiment is carried out using metal powders of copper, zinc, magnesium and leadreacted with oxygen respectively.Observations on the metal powders of copper, zinc, magnesium and lead in theexperiments are shown in Figure 2.2.




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Figure 2.2

(a) Look at the flame or glow in each diagram in Figure 2.2. Complete Figure 2.2 bystating the observations for the reaction of metal powders with oxygen.

[3 marks]




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(b) Complete Table 2.3 based on the experiment.

Name of variables Action to be taken

(i) Manipulated variable:

……………………...........

(i) The way to manipulatevariable:

…………………………………..

…………………………………..

…………………………………... (ii) Responding variable:

…………………………….

(ii) What to observe in theresponding variable:

…………………………………...

…………………………………...

…………………………………... (iii) Controlled variable:

…………………………….

(iii) The way to maintain thecontrolled variable:

…………………………………...

……………………………………

……………………………………

Table 2.3

(c) State one hypothesis for the experiment.

………………………………………………………………………………………..

……………………………………………………………………………………….. [3 marks]

(d) (i) Based on the observations in Figure 2.2, arrange copper, zinc, magnesium and

lead in descending order of reactivity of metal towards oxygen.

Descending order of reactivity of metal towards oxygen.

[3 marks]




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(ii) The experiment is repeated by using aluminium powder to react with oxygen.The result of the experiment is shown in Figure 2.4.

Set-up of apparatus Observation on the metal

Moderately bright flame

Figure 2.4

Predict the positions of aluminium in the Reactivity Series of metals in (d)(i).Draw an arrow ( ↓ ) in (d)(i) to show the position of aluminium in this reactivityseries.

[3 marks]




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(e)

Figure 2.5

Based on the observations in Figure 2.5, classify the metals into two groups, thosewhich are more reactive than carbon and those which are less reactive than carbon.Put your answer in a suitable table.

[3 marks]




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6 SPM 2005/P3/Q2 A pupil wanted to construct the electrochemical series.He measured the potential dfference of a few pairs of metals.The set up of the apparatus of his experiment is shown in Figure 2.1.

Figure 2.1

Figure 2.2 shows the results obtained from experiment after 30 minutes.

Figure 2.2

(a) Describe the change that you see in the copper(II) sulphate solution duringthe experiment.

………………………………………………………………………………………..

………………………………………………………………………………………..

……………………………………………………………………………………….. [3 marks]




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(b) The pupil repeated the experiment by substituting the zinc metal with iron,magnesium and lead.

Each time he used copper metal as the negative electrode and freshcopper(II) sulphate solution.The following table shows the voltmeter readings he obtained from the pairsof metals.

ExperimentPairs of metal Reading of

voltmeter/ VNegativeelectrode

Positiveelectrode

I Zinc Copper 1.10

II Iron Copper 0.78

III Magnesium Copper 2.72

IV Lead Copper 0.45

Based on the above information, complete the following table.

Manipulated variable:

………………………………………..

………………………………………..

………………………………………..

Method to manipulate thevariable:

……………………………………......

………………………………………..

………………………………………... Responding variable:

.........................................................

………………………………………...

………………………………………...

How the variable is responding:

………………………………………...

………………………………………...

………………………………………... Controlled variable:

………………………………………..

………………………………………..

………………………………………...

Method to maintain thecontrolled variable:

………………………………………...

………………………………………...

………………………………………...

(c) State the hypothesis for this experiment.

………………………………………………………………………………………..

………………………………………………………………………………………..

………………………………………………………………………………………..




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[3 marks]F4 Chapter 6 Electrochemistry

F5 Chapter 3 Oxidation & Reduction

1 SPM 2003/P2/Q5

(a) (i) Brown solid is formed.Blue solution turns colourless.

(ii) Green solution turns brown.Brown colour of bromine decolorizes.

(b) Mg + Cu2+ → Mg2+ + Cu(c) A substance that receives electron.

(d) (i) 0 → +2 (ii) copper(II) ion // copper(II) sulphate

(e) (i) redox(ii) 0(iii) oxidising agent(iv) chlorine water

2 SPM 2004/P2/Q3

(a) (i) A positively charged ion.(ii) Electrical → Chemical

(b) (i) Cu2+, SO42-, H+ , OH-

(ii) In the table below, write the ions in (b)(i) which moved to electrodes X

and Y.

Electrode X Electrode Y

SO4-

OH- Cu +

H+

(iii)Electrode X : Oxidation

Electrode Y : Reduction

(iv) Brown solid(v) Blue to colorless.(c) (i) Oxygen

(ii)20___ = 0.0008 mol

24000

(iii) 0.0008 x 6.02 x 1023




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3SPM 2005/P2/Q6

(a) (i)

(ii) A burning splinter gives a ‘pop’ sound. (iii) Na+ and H+ ions are attracted towards the cathode. H+ ions are selected to be

discharged as hydrogen gas.

(b) (i) MgO(ii) 2Mg + O2 → 2MgO (iii) Oxidation number for:

Magnesium = +2Oxygen = -2

4 SPM 2007/P2/Q6

(a) (i) water and oxygen

(ii)

(b) (i) Fe2+ and OH- ions combine to form iron(II) hydroxide.Iron(II) hydroxide is oxidised to iron(III) hydroxide.

Iron(III) hydroxide form hydrated iron(III) oxide/ rust.




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(ii) +2 → +3

(c) (i) Zinc is more electropositive than iron.Zinc atoms lose electrons more easily than iron.Zinc corrodes but iron does not.

(ii) Zn → Zn2+ + 2e

5 SPM 2004/P3/Q2

(a)

Metal Observations

ZincMagnesiumLead

Moderately bright flameVery bright flameBright flame

(b)Name of variables Action to be taken

(i) Type of metal (i) Replace the metal with differentmetals

(ii) Intensity of the flame (ii) Observe the intensity of theflame

(iii) Quantity of metal (iii) Use a constant mass of metal

(c) The higher the metal in the reactivity series, the brighter the intensity of the flame.

(d) (i)

Descending order of reactivity of metal towards oxygen.

(ii) Mg, ↓ , Zn, Pb, Cu

(e)

Metals more reactivethan carbon

Metals less reactivethan carbon

MagnesiumSodium

LeadCopper

6 SPM 2005/P3/Q2

(a) The blue colour of copper (II) sulphate solution fades.

(b) Manipulated variable:The metal as negative electrode

Method to manipulate thevariable: Replace the negative electrodewith different metals.

Responding variable:Voltmeter reading

How the variable is responding:The voltmeter reading changes.

Zn Pb CuMg




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Controlled variable:

Concentration of copper(II)sulphate solution,

copper metal

Method to maintain thecontrolled variable:Use copper(II) sulphate solution ofthe same concentration.

Use copper as the positiveelectrode.

(c) The greater the distance between two metals in the electrochemical series, thehigher the voltage reading.




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ANALYSIS OF PAST YEAR QUESTIONS FROM 2003 –

2008

Year 2003 2004 2005 2006 2007 2008

Paper

No.P2 P3 P2 P3 P2 P3 P2 P3 P2 P3 P2 P3

Type of

questionS E S E S E S E S E S E S E S E S E S E S E S E

Question

No

F4 Chp

6F5 Chp

3

5 3 3 4 2 6 9 2107 6 2

89

1 SPM 2003/P2/Sectio n C/Q3 (a) Lime juice was electrolysed using carbon electrodes.

What is produced at the cathode?Write a half-equation for the reaction.

[2 marks]

(b) Figure 6 shows two types of cell.

Figure 6

Compare and contrast cell P and cell Q. Include in your answer the observationand half-equations for the reactions of the electrodes in both cells.

[8 marks]

(c) A student intends to electroplate an iron key with a suitable metal to beautify it.Design a laboratory experiment to electroplate the iron key.Your answer should consist of the following:




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• Chemicals required• Procedures of the experiment• Diagram showing the set-up of the apparatus• Chemical equation involved in the reaction

• Observation [10 marks]

2 SPM 2004/P2/Sectio n C/Q4 (a) Explain what is meant by redox reaction using a chemical reaction.

[2 marks]

(b) Table 4 shows the result of two experiments to study the effects of metals Pand Q on the rusting of iron.

Table 4 (i) Explain why there is a difference in observations in Experiments I and II.(ii) Arrange in descending order metals P, iron and Q based on the

electropositivity of the metals.[8 marks]

(c) You are provided with strips of metals W, X, Y and Z and their salt solutions.Describe how you would show that the order of these metals in theelectrochemical series is W, X, Y and Z in descending order ofelectropositivity.Your explanation should include observations and conclusions.

[10 marks]




20

3 SPM 2005/P2/Q9 (a) You have an iron key that rusts easily.

State how you would solve this problem using an electrolysis process.

[4 marks]

(b) Electrolysis is carried out on a dilute sodium chloride solution using carbonelectrodes.Explain how this electrolysis occurs.Use a labelled diagram to explain your answer.

[6 marks]

(c) Aluminium is placed above zinc in the electrochemical series. Aluminium and zinc can be used to build a chemical cell, using suitable

apparatus and the following chemicals; Aluminium sulphate solution

Zinc sulphate solutionSulphuric acid solution

Describe how you build this chemical cell.Include a labelled diagram in your answer.On your diagram, mark the direction of the electron flow, the positive terminaland the negative terminal.

[10 marks]

4 SPM 2006/P2/Q7

(a) The following are the formulae of two compounds. Al2O3 Cu2O

(i) Based on the two formulae, state the oxidation number for aluminium andcopper.

[2 marks]

(ii) Name both the compounds based on the IUPAC nomenclature system.

[2 marks]

(iii) Explain the difference between the names of the two compounds basedon the IUPAC nomenclature system.

[2 marks]

(b) Diagram 7 shows the set up of the apparatus for an experiment to investigateelectron transfer through a solution.




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Diagram 7

(i) Name the oxidation agent in the experiment. [1 mark ]

(ii) Write the half equations for the reactions that occur at the negative andpositive terminals.

[5 marks](iii) Based on your answer in 7(b)(ii), describe the oxidation and reduction

process in terms of the electron transfer that occurs at the negative andpositive terminals.State also the changes that can be observed after 10 minutes.

[8 marks]

5 SPM 2008/P2/Q8 Diagram 8.1 shows the apparatus set-up for the electrolysis of sodium chloridesolution using carbon electrodes.

Diagram 8.1 (a) Based on Diagram 8.1, state the factors that determine the products formed at

electrode P and electrode Q.[2 marks]

(b) Explain the reactions at electrodes, P and Q. Include the following in yourexplanation:




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• List of ions attracted to each of electrodes, P and Q• Names of the ions selectively discharged at each electrode• The reason why the ions are selectively discharged• Half equations for each reaction

[10 marks]

(c) An experiment is carried out to determine the relative position of three metals,silver, L and M, in the electrochemical series. Diagram 8.2 shows the results ofthe experiment.

Diagram 8.2

(i) Based on the results, arrange the three metals in order of increasingelectropositivity.Explain your answer.

[6 marks]

(ii) If M is copper, name the product formed in experiment II.

[2 marks]

6 SPM 2008/P2/Q9 (a) A metal M reacts with oxygen to form an oxide. The oxide is very soluble in

water to produce an alkaline solution.Suggest the identity of metal M and describe an observation when the metal youhave named reacts with oxygen.Write the half-equations for oxidation and reduction for the reaction.

[4 marks]




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(b) Diagram 9 shows an apparatus set-up to investigate the effect of two differentmetals, X and Y on the rusting of iron, Fe.

Diagram 9

The result of this experiment after three days is shown in Table 9.

Pair of metals Observation

Fe, X Dark blue colour

Fe, Y No change

Table 9

Based on Table 9, suggest the identity of metals, X and Y.Give two reasons for each of your choices.[6 marks]

(c) Iron(II) ions can be converted to iron (III) ions and iron(III) ions can be convertedback to iron(II) ions. By using a named metal as a reducing agent and a namedhalogen as an oxidising agent, describe briefly how you would carry out thesetwo conversions.Describe a test to show that each conversion has taken place.

[10 marks]




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7 SPM 2007/P3/Q2

Diagram 2 shows several electrochemical cells with different voltages.

Diagram 2

Identify the factor that influences the differences in the voltages.

Plan a laboratory experiment to construct an electrochemical cell to determine onefactor that influences the differences in the voltage.Your planning should include the following:

(i) Statement of the problem

(ii) All the variables(iii) Hypothesis

(iv) List of materials and apparatus

(v) Procedure

(vi) Tabulation of data

[17 marks]




25


1 SPM 2003/P2/Sectio n C/Q3 (a) Hydrogen gas.

2H+ + 2e → H2

(b) Cell P Cell Q

Type of cell Electolytic cell Chemical/voltaic cell

Energy change electrical → chemical chemical → electrical Name of electrode Both electrodes are copper Copper = positive

electrodezinc = negative

elctrode

Ions in electrolyte Cu2+, SO42-,

H+ , OH- Cu2+, SO4

2-,H+ , OH-

Half equations At anode:Cu → Cu2+ + 2e

At cathode:Cu2+ + 2e → Cu

Zn → Zn2+ + 2e

Cu2+ + 2e → Cu

Observation At anode:Copper dissolves.

At cathode:

Brown solid forms.

Zinc dissolves.

Brown solid forms.

(c) To electroplate a key with silver:Chemicals required:

silver, silver nitrate solutionProcedures of the experiment:

Key is made the cathode.Silver is made the anode.Electrolyte used is silver nitrate solution in a beaker.The silver anode and the key are immersed into the electroyte andconnected to a battery.

Diagram showing the set-up of the apparatus




26

Chemical equation involved in the reaction:

At anode: Ag → Ag+ + e

At cathode: Ag+ + e → Ag

Observation:

At anode:Silver dissolves.

At cathode:Shiny solid forms.

No change in the colour of the solution.

2 SPM 2004/P2/Sectio n C/Q4 (a) Redox reaction is a reaction in which oxidation and reduction occur

simultaneously.E.g: Mg + Cu2+ → Mg2+ + Cu

(b) (i) In Experiment I,Iron is oxidised to Fe2+ ions.Electrons flow from iron to P because iron is more electropositive than P.Blue solution shows the presence of Fe2+ ions.

In Experiment II,

Q is oxidised.Electrons flow from Q to Fe because Q is more electropositive than Fe.




27

Water and oxygen receive electrons to form OH- ions.The pink spots show the presence of OH- ions.

(ii) Q, iron, P

(c)

Salt SolutionMetal

W X Y Z

W

X X

Y X X Z X X X

√ = Metal deposited X = No deposit

Fill 4 test tubes with salt solutions of metal W, X, Y and Z.Clean the metal strips with sandpaper.Put metal W in to every test tube.Leave for a few minutesRepeat the steps above using metlas X, Y and Z.

Observation:For metal W:Metal deposition occur when metal W is immersed into salt solutions of X, Yand Z.Therefore, W is the most electropositive.

For metal Z:No metal deposition when metal Z is immersed into salt solutions of W, X andY.Therefore, Z is the least electropositive.

For metal X:There is metal deposition when metal X is immersed into salt solutions of Y and

Z.There is no metal deposition when metal X is immersed into salt solution of W.Therefore, X is more electropositive than Y and Z.

For metal Y:There is metal deposition when metal Y is immersed into salt solution of Z.No metal deposition occur when metal Y is immersed into salt solutions of Wand X.Therefore, Y is more electropositive than Z.

Descending order: W, X, Y, Z




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3 SPM 2005/P2/Q9 (a) The iron key can be electroplated with nickel by electrolysis.

The iron key is made the cathode.Nickel is made the anode.Nickel(II) sulphate is used as the electrolyte.

(b)

Ions present in sodium chloride solution are Na+ , Cl- , H+ , OH- ions.Na+ and H+ ions are attracted to the cathode.

Cl-

and OH-

ions are attracted to the anode. At the cathode, H+ ions are selected to be discharged because it is lower thanNa+ ions in the electrochemical series.Hydrogen gas is produced at he cathode.

At the anode, OH- ions are selected to be discharged because it is llower thanCl- ions in the electrochemical series.Oxygen gas is produced at the anode.

(c)

Dilute sulphuric acid is filled into a U-tube. Aluminium sulphate solution is added into one arm of the U-tube and zinc

sulphate solution is added into the other arm of the U-tube, slowly. Aluminium and zic plates are immersed respectively into aluminium sulphateand zinc sulphate solution.The wire is connected to complete the circuit.

4 SPM 2006/P2/Q7

(a) (i) Oxidation number of Al = +3

Oxidation number of Cu = +2

(ii) Al2O3 = aluminium oxideCu2O = copper(II) oxide




29

(iii) Copper exhibits more than one oxidation number. Therefore the romannumber is used in naming copper(II) oxide.This is not required to name aluminium oxide because aluminium only

exhibits one oxidation number.

(b) (i) acidified potassium manganate(VII) solution

(ii) At positive terminal:MnO4

- + 8H+ + 5e → Mn2+ + 4H2O

(iii) At positive terminal, MnO4- ions receive electrons and are reduced to Mn +

ions. At the negative terminal, Fe2+ ions donate electrons and are oxidised toFe3+ ions.

The purple colour of potassium manganate(VII) solution fades.The green colour of iron(II) sulphate solution to brown.

5 SPM 2006/P2/Q10

(a) sodium chloride

(b) At anode: 2Cl- → Cl2 + 2e //

At cathode: Na+ + e → Na

(c)

(d) During electrolysis of molten sodium chloride,chloride ions are attracted to the anode whereas sodium ions are attracted tothe cathode. At the anode, Cl- ions are discharged to form chlorine gas.2Cl- → Cl2 + 2e At the cathode, Na+ are discharged to form sodium.Na+ + e → Na

6 SPM 2008/P2/Q8

(a) At electrode P/ cathode:the position of ions in electrochemical series




30

At electrode Q/ anode: concentration of ions(b)

Electrode P/cathode Q/anode

Ions attracted Na+

, H+

Cl-

, OH--

Ions selectively discharged Hydrogen ion Chloride ion

Reason H+ ions is lower in theelectrochemicalseries

Concentration ofCl- ions is higherthan OH- ions

Half equation 2H+ + 2e → H2 2Cl- → Cl2 + 2e

(c) (i) Experiment I II III

Explanation

L is moreelectropositivethan silver.

L can displacesilverfrom itssolution

M is moreelectropositivethan silver.

M can displacesilverfrom itssolution

L is moreelectropositivethan M.

M cannot displace Lfrom its solution.

Order of the three metals: silver, M, L

(ii) copper(II) nitrate

7 SPM 2008/P2/Q9 (a) M is sodium.

[Alternate Answer: any other Group 1 metals]

Sodium burns with a yellow flame to produce a white solid.

Oxidation: Na Na+ + e

Reduction: 02 + 4e 202-

(b)X is copper.

[Alternate Answer: any other metal less electropositive than iron.

Copper is less electropositive than iron.

Therfore, iron rusts.

Y is magnesium.[Alternate Answer: aluminium or zinc]




31

Magnesium is more electropositive than iron.

Therefore, magnesium prevents iron from rusting.

(c) Fe

3+

Fe

2+

Reducing agent is magnesium. Add magnesium to a solution containing Fe3+.Heat the mixture.Filter the mixture. Add sodium hydroxide solution. A green precipitate is formed.

Fe2+ Fe3+

Halogen is bromine. Add bromine water to a solution containing Fe2+.Shake the mixture.

Add sodium hydroxide solution.Brown precipitate is formed.

8 SPM 2007/P3/Q2

(i) Statement of the problem:How does the distance between two metals in the electrochemical seriesaffect the voltage produced in a cell?

(ii) Manipulated variable: Pair of metalsResponding variable: Voltage of cellConstant variable: Type of electrolyte

(iii) Hypothesis:The further apart the distance between two metals in the electrochemicalseries, the higher the voltage produced.

(iv) Materials:iron, zinc, magnesium, copper and aluminium strips; copper(II) sulphatesolution

Apparatus:voltmeter, beaker, sand paper and connecting wires

(v) Procedure:1. A beaker is filled with copper(II) sulphate solution.2. The copper and magnesium strips are cleaned with sand paper.3. The strips are immersed into the solution and connected by wires

to a voltmeter.4. The reading of the voltmeter is recorded.5. Steps 1 - 4 are repeated with zinc, iron and aluminium.

(vi) Tabulation of data:

Metal pair Voltage/ V

Mg - Cu

Zn - Cu

Fe - Cu Al - Cu




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Electrochemistry and Oxidation and Reduction