C12 TAHAP 2 PAIZAH

8/4/2019 C12 TAHAP 2 PAIZAH

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4541/CHEMISTRY MODUL P3T ( TAHAP 2)

OXIDATION & REDUCTION1.1 DEFINITION

1. REDOX REACTIONS are reaction where oxidation and .occur

2. Oxidationinvolved :

.of electron

losses of .

gains of.

. oxidation number.

3. Reduction involved :

.of electron

losses of .

gains of.

. oxidation number.

4.

Magnesium atom is oxidisedbecause :

magnesium atom . electrons.

the oxidation number of magnesium . from .. to

..

5.

Hydrogen sulphide is oxidised to . It acts as an

. agent.

Chlorine gas is reduced to . It undergoes reduction and acts

as an . agent.

JPNT 2009 CHAPTER 3 : OXIDATION AND REDUCTION

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Mg Mg2+ + 2e

H2S + Cl2 S + 2HCl


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6.

(a) Zn Zn2+ + 2e

Zinc atom undergoes because its .. electrons.

Its oxidation number increases from to

Zinc acts as an ..agent

(b) 2H+ + 2e H2

Hydrogen ion undergoes because it .. electrons.

Its oxidation number from to

Hydrogen ion acts as an ..agent.

7.

Copper(II) ion undergoes .

It.. electrons.

Its oxidation number decreases from .to

Copper(II) ion acts as an.agent.

Mneumenic method of remembering

OIL RIGOxidation Is Loss electron, Reduction Is Gain electronLEO GERLoss electrons Oxidation, Gain electrons Reduction

1.2 REDOX REACTION IN TERMS OF CHANGE IN OXIDATION NUMBER

EXERCISE 1Calculate the oxidation number in the underlined element

a. MnO2

b. MnO4

c. Mn2O3

d. Na2CrO4


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Zn + 2HCl ZnCl2 + H2

Cu2+ + 2e Cu


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e. K2Cr2O7

f. HNO3

EXERCISE 2

Determine which of the reaction is oxidation, reduction or neither.Tentukan perubahan manakah diantara berikut adalan pengoksidaan, penurunan atau bukankedua-duanya.

ReactionsChanges in oxidation

numberProses

Cu 2+ Cu Cu : 2 + to 0 Reduction

Br2 Br-

MnO4 - Mn 2+

IO3- I2

CrO42- Cr3+

FeCl2 FeCl3

SnO SnO2

NaNO2 NaNO3

Cr2O72- Cr3+

Zn Zn2+

NH3 NO

1.3 ANALYSING REDOX REACTIONS IN :

1.3.1 Displacement of metals from its salt solution.

1.3.2 Electrolytic and Chemical Cell (Voltaic cell)

1.3.3 Rusting of Iron // Corrosion of Metal

1.3.4 Displacement of halogen from its halide solution.

1.3.5 Change of : Fe2+ Fe3+ and Fe3+ Fe2+

1.3.6 Transfer of electron at a distance.


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1.3.7 Reactivity Series of Metals and Its Applications.

1.3.1 DISPLACEMENT OF METALS FROM ITS SALT SOLUTION.

Electrochemical Series :

Electrochemical Series is an arrangement of elements according to their tendency

to electrons to form a positive ion (cation).

Electrochemical Series

K Na Ca Mg Al Zn Fe Sn Pb H Cu Hg Ag Au

Mneumonic method of memorizing the series

Kalau Nak Cari Mangkuk Aladdin Zon Felda Sediakan Peluang Hingga Cuba Hubungi

Abang Aku

The . the position of the metal in the Electrochemical Series,

the is the tendency of the metal atoms to .

electrons (become moreElectropositive).

Displacement of metals :

The metal which is higher in the electrochemical series will its

. to the metal which is lower in the electrochemical

series from its salt solution. The more electropositive metal will be and

dissolves. The less electropositive metal ion will be . and deposited


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Electropositivity decreases


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EXERCISE 3

An experiment is carried out to determine the relative position of 3 metals, silver, L and M, inan electrochemical series. Diagram below shows the results of the experiment.

Observation Grey deposit

Colourlesssolution

Greydeposit

Lightblue solution

Nochange

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

(ii)If M is copper, name the products formed in Experiment II. Write the chemical equation forthe reaction.


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A


1.3.2 ELECTROLYTIC AND CHEMICAL CELL (VOLTAIC CELL)

(a) Differences between an electrolyticcell and a chemicalcell :

CHARACTERISTIC ELECTROLYTICCELL CHEMICAL CELL

Set up ofapparatus

Has . Has no..

Has Has Voltmeter

Same type ofelectrodes type ofelectrodes

EXERCISE 4

1. Diagram 1 and 2 shows two different cells. Based on the diagram, answer the followingquestions


80

V


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(a) Referring to the Diagram 1

(i) State all the ion in the electrolyte.

(ii) State the anode and cathode. Namakan elektrod anod dan katod.

anode : ........................................................

cathode : ..........................................................

(iii) Write the half equation at

Anode:

Cathode:.

(iv) Name the ion that is

Oxidized:

Reduced:

(b) Referring to Diagram 2

(i) State the negative and positive terminal. Namakan elektrod positif dan negatif.

Positive : ........................................................

Negative : ............................................

(ii) Write the half equation for the reaction at copper and plate. Tuliskan persamaansetengah bagi tindak balas dikepingan zink dan kuprum dalam Rajah 2.

Copper plate:.....................................................................................................

Zinc plate:..........................................................................................................

(iii) Name the ion that is

Oxidized:............................................................................................................

Reduced:............................................................................................................

(iv) Name the

Oxidizing agent:

Reducing agent:


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(v) State the electron movement in the outer circuit.

.

(c) State the changes in energy in

Diagram 1:

Diagram 2:

1.3.3 RUSTING OF IRON // CORROSION OF METAL

Corrosion of metal isa redoxreaction in which a metal atom ..to

its ion by .electrons.

When metal corrodes, it usually forms a metal oxide coating.

Aluminium oxide, for example is non porous and firmly coated the metal. It will

protect the aluminium underneath from further corrosion. This further explain the

resistance of aluminium to corrosion even though it is higher in the

Electrochemical Series ( electropositive metal). Other metals with similar property

are zinc, lead, nickel and chromium.

Rusting of iron/corrosion of iron.

Rusting of iron takes place when iron corrodes in the presence of..and..

It is a redox reaction whereby oxygen acts as an .while ironacts as a .

Mechanism of rusting of iron.

The surface of iron at A becomes an anode (negative terminal), the electrode at

which oxidation occurs.

Iron atom, Fe loses electrons and is.. to form iron(II) ion, Fe2+


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O2 O

2

B A

Iron

Water dropletO

2

B


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Half equation of oxidation :.

The electrons flow through iron to the edge of the water droplet at B,where the concentration of oxygen here is higher.

The iron surface at B becomes cathode( positive terminal) , the electrode atwhich reduction occurs. Oxygen, O2 gains electrons and is .toform hydroxide ions, OH-.

Half equation of reduction :..

The iron(II) ion, Fe2+ produced combines with hydroxide ions, OH- toform iron(II) hydroxide.

Fe2+ + 2OH- Fe(OH)2

Overall equation for rusting:2Fe + O2 + 2H2O 2Fe(OH)2

Iron(II) ion, Fe2+ is ..but rust is

..because iron(II) hydroxide , Fe(OH) 2 undergoes further

oxidation by oxygen to form hydrated iron(III) oxide, Fe2O3 .xH2O (rust).[xis an integerwhereby the value varies ]

Iron(II) hydroxide , Fe(OH)2 is oxidized by oxygen to form iron(III)hydroxide, Fe(OH)3

Then, iron(III) hydroxide, Fe(OH)3 is decomposed to form hydrated

iron(III) oxide (rust).

Rust is brittle, porous and not tightly packed. Thus, water and oxygen can

penetrate the metal underneath. Iron will undergo continuous corrosion.

Rusting of iron occurs ..in the presence of

.orsalt because when these substances dissolve in water, the

solutions becomes better electrolyte. An electrolyte will increase the

electrical conductivity of water.

Iron structures at coastal and industrial areas rust faster because of :

the presence ofsalt in the coastal breeze

the presence ofacidic gases in industrial area such as sulphur dioxide, SO2

and nitrogen dioxide, NO2.


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ControllingMetal Corrosion

(i) Metal corrosion can be controlled by using other metal.

K Na Ca Mg Al Zn Fe Sn Pb Cu Ag

Ease of releasing electron increases (more electropositive)

When iron is in contact with .metal for examplezinc, rusting of iron is prevented.

Zinc, Zn loses electrons more easily than iron, Fe. Zinc corrodes oris.. instead of iron.

Half equation of oxidation : The electrons that are released by zinc flow through the iron to the metalsurface where there is water and oxygen.

Half equation reduction :

When iron is in contact with metal for example copper,rusting of iron is faster.

Iron, Fe loses electron more easily than copper, Cu. Hence, iron iscorrodes / rustsor.instead of copper.

Thefurther apart

the metals in the Electrochemical Series are, the the more electropositive metal corrodes.

EXERCISE 5

Referring to the above situation, planned an experiment to compare the corrosion of iron andsteelMerujuk kepada situasi di atas, rancangkan satu eksperimen makmal untuk membandingkankakisan besi dengan keluli.

Your planning must include the following:


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If the body of car is made up of iron, it is easily rust. The surface of iron is in contactwith air and water. It also easily dented during an accident. To overcome this problemthe body of a car is made up of steel.Jika badan kereta diperbuat daripada besi, ia mudah berkarat. Ini adalah kerana

permukaan besi terdedah kepada udara dan air, Ia juga mudah kemek apabilaberlaku kemalangan. Oleh itu, untuk mengurangkan masalah ini, badan keretadiperbuat daripada keluli.


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Perancangan eksperimen anda hendaklah mengandungi perkara-perkara berikut:

(i) Problem Statement /Pernyataan masalah

(i) Hypothesis:

(iii) Manipulated variable:

Responding variable:

Fixed/ Constant variable

(iv) Material:

(v) Apparatus

(vi) Diagram:

(vii)Procedure/Prosedur

1

2

3

4

5

6

(viii) Tabulation of data/Penjadualan data


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1.3.4 DISPLACEMENT OF HALOGEN FROM ITS HALIDE SOLUTION.

The halogen Halides ionF, Cl, Br, I, At F-, Cl-, Br-, I-, At-

The more electronegative halogen :

can attractelectrons from halides ion that are less electronegative

candisplaces less electronegative halogen from its halide solution

gains electrons and acts as an oxidizing agent.

undergoes reduction to form halide ions.

Example :

Chlorine molecule :

........................... two electrons.

Undergoes

acts as an agent.

The halide ions of the less electronegative halogen :

lose their electrons, undergoes oxidation, acts as a reducing agent.

Example :

Iodide ion :

. Electrons

Undergoes

acts as a . agent.


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Cl2 + 2e 2Cl-

2I- I2 + 2e

Electronegativity decreases


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EXERCISE 6

1 A few drops of chlorine water are added to 2 cm3 of potassium iodide solutionand the mixture is then shaken thoroughly.

Half equation forreduction : Cl2 + 2e- 2Cl-

Half equation foroxidation : 2I- I2 + 2e-

Ionic equation : Cl2 + 2I- 2Cl- + I2

Explanation :

Chlorine molecules, Cl2 electrons to form chloride ions, Cl- .

Chlorine molecule is

Iodide ions, I- to form iodine molecule, I2.

Iodide ions are..

Iodide ions have chlorine molecule, Cl2 . Iodide ion is

an. agent

Chlorine molecules, Cl2 has iodide ions. Chlorine is

a..agent.

2 Between these substances: zinc metal, chlorine water, iron(II) sulphate solution, copper(II)sulphate solution, there are substances that can act as oxidizing agent and reducing agentin a redox reaction.Diantara bahan berikut : logam zink, air klorin, larutan ferum(II) sulfat dan larutankuprum(II)sulfat, ada yang boleh bertindak sebagai agen pengoksidaan dan ada yang bolehbertindak sebagai agen penurunan dalam tindakbalas redoks.

(a) What is the color of bromine water? Apakah warna air bromin ?


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Chlorine water

Potassium iodidesolution


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

(b) State the oxidation number of chlorine in chlorine water. Nyatakan nomborpengoksidaan bagi klorin dalam air klorin.

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

(c) When iron(II) suphate solution is added with chlorine water, a chemical reaction takesplace and the oxidation number of chlorine change.Apabila larutan ferum(II)sulfatdicampurkan dengan sedikit air klorin, tindakbalas berlaku. Didapati keadaan

pengoksidaan klorin berubah.

(i) Write the chemical equation for the reaction. Tuliskan persamaan ion bagitindakbalas ini ?

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

(ii) What is the changes in oxidation number of chlorine? Berapakah perubahankeadaan pengoksidaan bagi klorin ?

.....................................................................................................................(iii) Name another substance that can change the oxidation number of chlorine as in (c)

(ii). Namakan satu bahan lain yang boleh menukarkan keadaaanpengoksidaan klorin seperti yang berlaku dalam tindakbalas ini.

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

(d) When excess zinc powder is stirred with copper(II) sulphate, the color of the solutionchanges and a solid is formed.Apabila serbuk zink yang berlebihan dikacau dengan

larutan kuprum (II) sulfat, warna larutan berubah dan satu pepejal terbentuk.

(i) Name the reducing agent in this reaction. Namakan agen penurunan dalamtindakbalas ini.

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

(ii) State the changes in the color of the solution. Nyatakan perubahan warna larutandalam tindakbalas ini.

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

1.3.5 CHANGE OF : Fe2+

Fe3+

AND Fe3+

Fe2+

(a) Changing of iron(II) ion, Fe2+ to iron(III) ion, Fe3+


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Bromine water

Iron(II) sulphatesolution

Heat


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Iron (II) ion, Fe2+ undergoes .by its electron to form iron(III) ion, Fe3+

Oxidation half equation :

The substance added is an oxidizing agent such as bromine water, Br2.

Bromine molecule gains electrons and undergoes .to form bromide ion,

Br-.

Reduction half equation :.

Observation for the change ofiron(II) ion, Fe2+ to iron(III) ion, Fe3+ :

(i) Iron(II) solution changes colour from pale green to yellow(ii) Brown colour of bromine water decolourises

Confirmatory test for iron(III) ion, Fe3+ :

Add sodium hydroxide solution to the solution until excess.

A brown precipitate is formed. It is insoluble in excess sodium hydroxide solution.

Other oxidizing agents that can replace bromine water to change Fe2+ to Fe3+ are :

Chlorine water, acidified potassium mangganate(VII), acidified potassiumdichromate(VI).

EXERCISE 7

1 The following is an equation represents a redox reaction.

Based on the redox reaction :

(a) Write half equation for :

(i) oxidation :

(ii) reduction :

(b) Name the substance that acts as :

(i) Oxidizing agent :.

(ii) Reducing agent :


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2Fe3+(aq) + H2S(g) 2Fe2+(aq) + 2H+ (aq) + S(s)


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(c) Change in oxidation number ;

(i) Oxidation number ofiron :..

(ii) Oxidation number ofsulphur:..

1.3.6 TRANSFER OF ELECTRON AT A DISTANCE.

1. Transfer of electron at a distance occurs when two solutions ofreducing agentand oxidizing agent areseparated by an..in a U-tube.

2. Redox reaction occurs as a result of through an external circuit.

3. Electrons flow from theagent (loseselectrons)to the ............agent(gains electrons) through the connecting wires and can be detected by agalvanometer.

4. Carbon electrode that is immersed in a .agent is known as the

negative terminal (anode).

5. Carbon electrode that is immersed in an ..agent is known as the

positive terminal (cathode).

6. The electrolyte allows the movement of.and completes the electric

circuit.

EXERCISE 8

1 An experiment is conducted to investigate the redoxs reaction using the apparatus in the

diagram below. Satu eksperimen telah dijalankan untuk mengkaji tindak balas redoks

menggunakan susunan radas saperti dalam rajah di bawah.

(a) What is the

function of

potassium chloride

solution?

Apakah fungsi

larutan kalium

klorida?


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(b) State the changes in the oxidation number of copper in the above reaction. Tuliskan

perubahan nombor pengoksidanan bagi kuprum dalam tindak balas ini.

.

(c) Write the half equation for the reaction at copper rod.

(d) Magnesium rod is an anode. Explain why? Rod magnesium adalah anod. Mengapa?

.

(e) Another experiment is conducted to investigate the redox reaction using the apparatus in

the above diagram. The reaction at the carbon rod is represented by the equation below.Satu eksperimen lagi, dijalankan untuk mengkaji tindak balas redoks menggunakan

susunan radas saperti diatas. Tindak balas yang berlaku di sekitar rod karbon boleh

diwakili oleh persamaan setengah tindak balas saperti berikut:

Mn O4- + 8H+ + 5e Mn 2+ + 4H2O

(i) What is the color changes at carbon rod?Apakah perubahan warna yang berlaku disekitar rod karbon?

.

(ii) Give the oxidation number for mangan in Mn O4-. Tentukan nombor pengoksidanan

bagi mangan dalam Mn O4- .

[The oxidation number of oxygen is -2]

..


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(iii) On the above diagram, mark the flow of electron by using an arrow. Pada rajah

diatas, tandakan arah aliran elektron dengan melukis anak panah.

(f) The above reaction is a redox reaction. Explain with the named example and referring to

the reactant of the example given, why neutralization is not a redox reaction.

Tindak balas yang berlaku dalam eksperimen ini ialah tindak balas redoks. Dengan

menamakan satu contoh bahan tindak balas dan merujuk bahan tindak balas yang

dinamakan itu, terangkan mengapa tindak balas peneutralan adalah bukan tindak balas

redoks.

..

..

..

.

1.3.7 REACTIVITY SERIES OF METALS AND ITS APPLICATIONS

(a) Reactivity series of metals is an arrangement of metals in accordance to the reactivityof their reactions with ..to form metal oxides.

K, Na, Ca, Mg, Al, C, Zn, H, Fe, Sn, Pb, Cu

(b) Application of the Reactivity Series

Metals that are located ..carbon in the Reactivity Series (lessreactive than carbon) can be extracted from their ores (metal oxides) using carbon.

Metals that are located carbon in the Reactivity Series (more

reactive than carbon) can be extracted from their ores (metal oxides) by electrolysis ofmolten ores using carbon electrode.


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Reactivity Decreases


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EXERCISE 9

1 Diagram 9 shows the the apparatus set up to investigate the redox reaction for 3 elementsX, Y and zinc. X is metal powder, Y is black powdered element. After heating according tothe procedure, the observation below is produced.

Diagram 9

Rajah 9 menunjukkan susunan radas satu eksperimen untuk mengkaji tindak balas redoks bagitiga unsur iaitu X, Y dan zink. X ialah serbuk logam, mankala Y ialah serbuk unsur berwarnahitam. Selepas dipanaskan beberapa ketika mengikut langkah-langkah pemanasan untukmendapat hasil tindak balas yang sempurna, pemerhatian berikut diperoleh.

Element/Unsur

Observation/Pemerhatian

During heating/ Semasapemanasan

After heating/Selepaspemanasan

XBurns brightly/Nyalaan

terangWhite powder/Serbuk putih

YBurns brightly/ Nyalaan

terangNo residue/Tanpa baki

ZinkGlows very brightly/Baraan

terang.......................................

(a) What is the function of potassium magganate(VII) in the experiment?Apakah fungsi kaliummangganat(VII) dalam eksperimen itu?

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


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(b) Describe the steps involved during heating to get the perfect product. Huraikan langkah-langkah pemanasan yang perlu dilakukan untuk mendapat hasil tindak balas yangsempurna.....................................................................................................................................

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

(c) Name the element X. Namakan unsur yang diwakili X.

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

(d) (i) State the observation when zinc is heated and cooled. Nyatakan pemerhatian bagi zinkselepas dipanaskan dan disejukkan.

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

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

(ii) Write the chemical equation for the reaction at zinc. Tuliskan persamaan kimia bagitindak balas yang berlaku ke atas zink itu.

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

(iii) State the changes in oxidation number of zinc in the above reaction. Nyatakanperubahan nombor pengoksidanan bagi zink dalam tindak balas itu.

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

(e) The residue from the heating of zinc is mixed with X and heated. The chemical reactiontakes place. Explain why the reaction is a redox reaction. Baki daripada pemanasan zinkdalam eksperimen itu digaul rata dengan X dan dipanaskan. Tindak balas berlaku.Terangkan mengapa tindak balas itu dikatakan tindak balas redoks.

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

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

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

(f) (i) Name the element Y. Namakan unsur yang diwakili Y.

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

(ii) Why is the product of heating Y left with no residue. Mengapakah hasil pemanasan Ytanpa baki?

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

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


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END OF CHAPTER 12

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C12 TAHAP 2 PAIZAH

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