chapter 3 - smk raja perempuan, ipoh files... · web viewstate the conditions for the rusting of...

WAJA F5 Chemistry 2010 Chapter 3 : Oxidation And Reduction

CHAPTER 3 : OXIDATION AND REDUCTION

A. REDOX REACTIONS

Learning Outcomes:You should be able to, state what oxidation is state what reduction is explain what redox reaction is state what oxidising agent is state what reducing agent is calculate the oxidation number of an element in a compound. relate the oxidation number of an element to the name of its compound using the IUPAC nomenclature. explain with examples oxidation and reduction processes in terms of electron transfer explain with examples oxidising and reducing agents in redox reactions. write oxidation and reduction half-equations and ionic equations.

Activity 11) The tables below describe the meaning of oxidation and reduction in terms of

(a) loss or gain of oxygen(b) loss or gain of hydrogen(c) transfer of electrons(d) changes in oxidation number

Study each table below carefully and fill in the blanks.(a) Loss or gain of oxygen

Loss or gain of oxygenOxidation Reduction

The process of gaining oxygen The process of losing oxygen Example : Mg + PbO MgO + PbIn the above redox reaction,

Mg gains oxygen to form MgO. This process is called. ……….………………………….

PbO loses oxygen to form Pb. This process is called ……….…………………………....

Mg is a reducing agent because it ………………….. … lead(II) oxide to …………………….

PbO is an oxidizing agent because it ………………… magnesium to………………………..

(b)Loss or gain of hydrogenLoss or gain of hydrogen

Oxidation ReductionThe process of losing hydrogen The process of gaining hydrogen

Example : H2S + Cl2 2HCl + S

In the above redox reaction H2S loses hydrogen to form S. The process is called …….. ………………………...

Cl2 gains hydrogen to form HCl. This process is called …….. ……………………….

H2S is a reducing agent because it ………………to …………………… ……..………….

Cl2 is an oxidizing agent because it ……………………to……………………………..

(c) Transfer of electrons

1

WAJA F5 Chemistry 2010 Chapter 3 : Oxidation And ReductionTransfer of electrons

Oxidation ReductionThe process of losing electrons The process of gaining oxygen

Example :Redox reaction: 2Na + Cl2 2NaCl Half-equations: Na Na+ + e // Cl2 + 2e 2Cl–

In the half-equations above, Na atom loses electron to form Na+. This process is called …………………………

Cl2 molecule gains electrons to form 2Cl–. This process is called …………………..

Na is a reducing agent because it …………………… to ………………………… ……..

Cl2 is an oxidizing agent because it …………………..to ………………………… …….

(d) Changes in oxidation number Changes in oxidation number

Oxidation ReductionThe increase in oxidation number The decrease in oxidation number

Example :Chemical equation: 2Na + Cl2 2NaCl

Changes in oxidation number Na : 0 +1 // Cl : 0 –1Given above are the changes in oxidation number of Na and Cl, state which element is oxidized or reduced and which element is the oxidizing or reducing agent.

Na is ............................. to Na+ : Na is the………………………………..… agent

Cl2 is …………………….to Cl– : Cl2 is the …………………………………. agent

2) What are redox reactions?

………………………………………………………………………………………………………………….

…………………………………………………………………………………………………………………..

Activity 2The diagram below shows the oxidation and reduction process that occurs in a redox reaction.

CuO + C → Cu + CO2

By drawing arrows, show and label the oxidation and reduction processes occurring in the redox reactions below.

ZnO + Mg MgO + Zn 2HI + Cl2 I2 + 2HCl

2

Reduction

Oxidation


Fe2O3 + 3CO 2Fe + 3CO2 2NH3 + 3Br2 N2 + 6HBr

Activity 3(a) Fill in the blanks with suitable words.

(i) The substance that causes oxidation is called the ………………………….………….. agent

(ii) The substance that causes reduction is called the ……………...…………………….. agent.

(b) State the oxidizing and reducing agents in each of the chemical reactions given below.(i) 2Zn + O2 2ZnO.

Oxidising agent: ……………………………... Reducing agent: …….…………………………..

(ii) 2Mg + CO2 2MgO + C

Oxidising agent: .…………………….……… Reducing agent: ……..……………………………..

Activity 4Oxidation numbers of elements can be calculated based on the ‘rules in assigning oxidation numbers’ as stated in the chemistry text book on page 107. Two examples are given below.

Examples:a) Determine the oxidation number for the underlined elements

(i) H3PO4

(1×3) + P + (-2×4) = 0 3 + P + (-8) = 0 P = 8 – 3 = +5 the oxidation number for phosphorus is +5

(ii) N2H4

2N + (1×4) = 02N + 4 = 0N = – 4/2 = –2 the oxidation number for nitrogen is –2

Answer the following questions.1. Determine the oxidation number for the underlined elements.(a) Fe (b) MgCl2 (c) Na2O

(d) CO2 (e) SO42– (f) MnO4

–

3


2. Calculate the oxidation number for chlorine and nitrogen in their compounds below and write its oxidation in the spaces provided.

3 Write the oxidation number for the underlined element in the boxes provided and state whether the element undergoes oxidation or reduction process. Part (a) is shown as an example

a) Mg + CuO MgO + Cu Process

b) 2Fe + 3Cl2 2FeCl3 Process

c) Cr2O72– Cr3+

Process

d) 4HCl + MnO2 MnCl2 + Cl2 + 2H2O

Process

e) Cu + 2AgNO3 Cu(NO3)2 + 2Ag

Process

4 Determine the oxidation number for the underlined elements in the table below and name the compound using the IUPAC nomenclature.

Formula of compound Oxidation number Name of compoundCuSO4

Cu2OCrCl3

Cr2O72–

NO3–

NO2–

NH4+

MnO2

Activity 5

Chlorine compound

HCl HClO HClO2 ClO2 HClO3 HClO4

Nitrogen Compound

NH3 N2O NO NO2– NO2 NO3

–

4

0 +2Oxidation

Substance undergoes oxidation:

Substance undergoes reduction:

Oxidising Agent: Reducing Agent:

Oxidation half-equation: Reduction half-equation:

Mg + 2HCl MgCl2 + H2





Pb + Br2 PbBr2






For each of the chemical reactions below,(a) write the oxidation and reduction half-equations, (b) identify the following: (i) Substance that undergoes oxidation (iii) Oxidising agent (ii) Substance that undergoes reduction (iv) Reducing agent

Example:Zn + 2Ag+ Zn2+ + 2Ag

Based the ionic equation given, it is known that the oxidation number of Zn increases from 0 to +2. Hence zinc undergoes oxidation to form Zn2+

Answer:Oxidation half-equation: Zn Zn2+ + 2e- Reduction half-equation: 2Ag+ + 2e- 2AgSubstance undergoes oxidation: Zinc (Zn)Substance undergoes reduction: Silver ion (Ag+)Oxidising agent : Silver ion (Ag+)Reducing agent : Zinc (Zn)

Based on the chemical equation given, complete the flow charts below.a)

Cl2 + 2I 2Cl + I2

b)

c)

5

4Na + O2 2Na2O






d)

Activity 6(a)Writing ionic equation from given oxidation and reduction half-equations:Example: Given: Oxidation half-equation: Mg Mg2+ + 2e Reduction half-equation: Ag+ + e Ag[In order to write an ionic equation from the two given half-equations, the electrons that were transferred from Mg to the Ag must be equal. Hence two Ag+ will receive two electrons from an atom of Mg.]

Mg Mg2+ + 2e 2Ag + + 2e 2Ag

Mg + 2Ag+ Mg + 2Ag

Answer: Ionic equation: Mg + 2Ag+ Mg + 2Ag

Based on the given oxidation and reduction half-equations, write the ionic equation for the reaction

(a) Oxidation half-equation: Mg Mg2+ + 2e Reduction half-equation: Cu2+ + 2e Cu

Ionic equation: …………………………………………………………………………………

(b) Oxidation half-equation: Al Al3+ + 3e

6

WAJA F5 Chemistry 2010 Chapter 3 : Oxidation And Reduction Reduction half-equation: Ag+ + e Ag

Ionic equation: …………………………………………………………………………………

(c) Oxidation half-equation: Fe2+ Fe3+ + e Reduction half-equation: Br2 + 2e 2Br–

Ionic equation: …………………………………………………………………………………

(d) Oxidation half-equation: 2I– I2 + 2e Reduction half-equation: Cl2 + 2e 2Cl–

Ionic equation: …………………………………………………………………………………

(e) Oxidation half-equation: Cl2 + 2e 2Cl– Reduction half-equation: Fe2+ Fe3+ + e

Ionic equation: …………………………………………………………………………………

(f) Oxidation half-equation: Fe Fe2+ + 2e Reduction half-equation: O2 + H2O + 4e 4OH–

Ionic equation: …………………………………………………………………………………

Activity 6(b)Changing Iron(II) ions, Fe2+ to Iron(III) ions, Fe3+

Procedure:1. 2.0 cm3 of ............................................. solution is added into a test tube.

2. A few drops of ...................... …….............. were added drop by drop into the test tube and

mixture is heated.

3. The ……………………………… is recorded.

4. Observation:

The colour of iron(II) sulphate solution changed from ....................... to ................... The bromine

water changed from ....................... to ........................ . In order to detect presence of iron(III) ion

in the solution, add .......................... ........................................ ………............... in excess.

..................................(colour) precipitate of iron(III) hydroxide is formed.

7

(1) 2.0 cm3 of Iron(II) sulphate solution

(light green)

WAJA F5 Chemistry 2010 Chapter 3 : Oxidation And Reduction5. Concept: a) Iron(II) ion is ……………… to iron(II) ion by ……………………………. At the same time

…………… …………………………… is reduced to ……………………………. Ion.

b) Oxidation and reduction half-equations:

Fe2+ ............. + .............. (Oxidation) Br2 + ............ .................. (Reduction)

c) Ionic equation: ………………………………………………………………………………………..

d) Iron(II) ions .................. electrons to become iron(III) ions. Iron(II) ions are ...................................

e) Bromine molecules ............. electrons to form bromide ions. Bromine molecules are ………….....

f) Reducing agent: ................................... Oxidising agent: ...................................

Changing Iron(III) ions, Fe3+ to Iron(II) ions, Fe2+

Procedure:1. Add 2.0 cm3 of ............................................. solution into a test tube.

2. Add ......................................... into the same test tube and heat the mixture.

3. Record the .............................................................

4. Observation:

a. The colour of iron(III) chloride solution changed from ............................ to ..............................

b. In order to detect the presence of iron(II) ion in the solution, add ................. ...................... in

excess. A ................ ........................... (colour) precipitate of iron(II) hydroxide is formed.

5. Concept: a). Iron(III) ion is ....................... to iron(II) ion by ................. ….................. At the same time, zinc

is ......................... to .............................. ion.

b) Reduction and oxidation half-equations:

Fe3+ + .......... .............. (Reduction) Zn ............... + ................ (Oxidation)

c) Ionic equation: ……………………………………………………………………………………

d) Iron(III) ions …............. electrons to become iron(II) ions. Iron(III) ions are ….......................

e) Zinc atom …................. electrons to form …................ ions. Zinc atoms are ….......................8

(1) 2.0 cm3 of iron(III) chloride solution (yellow)


f) Reducing agent: ...................................... Oxidising agent: ........................................

Activity 7Displacement of metal from its salt solution

M(s) + AB(aq) MB(aq) + A(s)

Oxidation half-equation: M Mn+ + ne

The following statements describe the displacement of metal from its salt solution by another element. Fill in the blanks with the correct word(s).

1. A ..…………. (more/ less) electropositive element is oxidized more …………………. (easily /

harder ) and acts as a ……………………….. (stronger / weaker) reducing agent.

2. An element that is located higher in the electrochemical series can displace other elements that

are positioned (i)……………………….. in the electrochemical series from its salt solution.

Example: Displacement copper from copper(II) sulphate solution.Ionic equation: Zn + CuSO4 ZnSO4 + CuHalf-equation: Zn Zn2+ + 2e [ Oxidation ]Half-equation: Cu2+ + 2e Cu [ Reduction ]

Zinc, Zn is (ii) ……………. electropositive than copper, Cu.

Thus Zn atom releases (iii) ……………. electron to form ion Zn2+.

The electrons are transferred from (iv)…………… ……….….. to (v)……………………………..

The copper(II) ion, Cu2+ receives the two electrons from zinc to form copper atom, Cu.

Zn atom acts as a (vi) …………………… …………… and Cu2+ ion acts as

a (vii) ………………………………… …………………

Activity 8 (a)Halogen in aqueous and 1,1,1-trichloroethaneComplete the table below by stating the colur of halogen in aqueous solution and in 1,1,1-trichloroethane

HalogenColour of halogen

In aqueous solution In 1,1,1,-trichloroethane

Chlorine

Bromine

Iodine

Displacement of halogens from their halide solutions by other halogens.

9


Fill in the blanks by choosing the most appropriate word from the list displayed above.

1) Halogens are located in Group ………….. of the Periodic Table

2) Halogen elements tend to ………………… electrons to achieve a stable octet electron arrangement.

3) Halogens are reduced to …………… ions

4) The electronegativity of halogens or their tendency to accept electrons ………………….. when going down Group 17.

5) Thus, the strength of halogens acting as ………………… ….……….. decreases when going down the group 17.

6) In displacement reaction of halogen, a ……….. electronegative halogen will displaces

a …………… electronegative halogen from its halide solution.

Activity 9Transfer of electrons at a distance

A. The diagram shows the set up of apparatus for the redox reaction involving bromine water and potassium iodide solution.

The following statement describe the redox reaction between bromine and potassium iodide solution. Fill the blanks with the appropriate word(s).

1. Electrons flow from …………….. to ….…………through the wire.

2. The colour of potassium iodide solution changes from ………………………to ……………………….

3. The colour of bromine water changes from ………………… to ………………… ……………………....

10

WAJA F5 Chemistry 2010 Chapter 3 : Oxidation And Reduction4. Oxidation half-equation: …………………………………………………………………………………..

Reduction half-equation: …………………………………………………………………………………..

5. Overall Ionic Equation : ……………………………………………………………………………………..

6. Oxidising agent: ……………………………… 7. Reducing agent: …………………………

7. To confirm that the brown solution formed is iodine solution, a chemical test can be carry out.

Method 1Some ....................... ......................... is added into a test tube containing the brown solution. A

dark blue colouration is obtained if iodine is present.

Method 22 cm3 of ........................................... is added into a test tube containing the brown soltion. The

test tube is then stopperred and its mixture .................. If the lower layer [1,1,1-trichloroethane

layer] is ............................. in colour, then it is confirmed iodine is present.

B The diagram below shows the set up of apparatus of redox reaction between acidified potassium manganate(VII) and potassium iodide soultion.

Below are some of the facts about the redox reaction between acidified potassium manganate(VII) and potassium iodide soultion. Answer the following question

The half-equation for the reaction that occurs around the carbon rod on the left is as followMnO4

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

a) State the change in oxidation number of manganese.

…………………………………………………………………………..

b) A brown solution was observed forming around the carbon rod on the right. Name the brown

solution formed. ..………………………………………………………………………………..c) Write a half-equation for the formation of the brown solution.

………………………..…………………………………………………………………………..

11

Carbon rod

Acidified Potassium Manganate (VII) solution, 1.0 mol dm-3

Potassium Iodide Solution, 1.0 mol dm-3

Dilute Sulphuric acid, 1.0 mol dm-3

WAJA F5 Chemistry 2010 Chapter 3 : Oxidation And Reductiond) Write the ionic equation for the reaction between acidified potassium manganate(VII) and iodide

ion.

…………………………………………………………………………………………………………….

e) On the diagram above, show the direction of the flow of electron by using arrows.

B. RUSTING AS A REDOX REACTION

Learning Outcomes :You should be able to,

state the conditions for the rusting of iron state what corrosion of metal is. describe the process of rusting in terms of oxidation and reduction. generate ideas on the use of other metals to control rusting, explain with examples on the use of a more electropositive metal to control metal corrosion,

Activity 10Rusting as a redox reaction

1. Fill in the blanks with suitable word.

a) Oxidation of metal is called (i) ………………………….. while (ii) the oxidation of iron is called

……………………

Oxidation half-equation for corrosion of metal: M Mn+ + ………….

b) The presence of (i)……………………. and (ii)……………………………. will cause iron to rust,

The rusting can be accelerated by adding (iii)………………………. or (iv) ……………………….

c) Copper forms a green coating as a result of corrosion, it contains ……………….. ions.

d) Metals like (i)………………………. and (ii)……………………… forms a very tough oxide layer

which adhere tightly to the surface of the metal and thus preventing further oxidation. This

protect the metals from further corrosion.

e) To prevent corrosion, metal A can be coated with a layer of metal B which is more (i)

………………………. than A. Metal B will corrode first, thus preventing metal A from corrosion.

In this situation, metal B is also called the (ii)……………………. metal.

f) If iron is in contact with another (i)…………………………which is less electropositive than iron,

the rate of rusting for iron will be (ii)………………………………….

g) Zinc is used to protect iron or steel by coating a thin layer of zinc onto it, this process is called

(i)……………………………….. In industry, zinc is chosen to serve the purpose rather than

other metals because zinc is (ii)…………………………………… in cost.

h) Some household and bathroom equipments are coated with a layer of shiny finishes, the

metals usually used for these coatings are (i)…………………………. and (ii)

………………………………………. .12


2. Mechanism of rusting of iron in the present of water and oxygen involves some chemical

reactions. Figure below shows an unlabeled diagram of a water droplet on the surface of iron.

Write the chemical equations or half equations for the processes below.

a) The formation of iron(II) ions from the metal:When iron contacts with water, the iron surface oxidizes to form iron(II) ions.

Oxidation half-equation: ……………………………………………………………………….

b) The formation of hydroxide ions:Electrons released by iron then flow to the edges of the water droplets, where there is a high concentration of dissolved oxygen. At the cathode area, water and oxygen molecules receive electrons and are reduced to form hydroxide ions.

Reduction half-equation: ……………………………………………………………………………..

c) Formation of green precipitate.Fe2+ readily combines with OH- to form insoluble solid Fe(OH)2

Chemical equation: …………………………………………………………………………………..

d) Using chemical equations in (a), (b) and (c), the reaction between iron, water and oxygen to form iron(II) hydroxide can be summarized into a overall chemical equation.

Chemicall equation: ……………………………………………………………………………………..

e) With excess oxygen, the rust is formed:The Fe2+ ions are further oxidized to form Fe3+ ions, which reacts with OH- ions to form the hydrated iron (III) oxide, Fe2O3. xH2O, known as ‘rust’.

Chemical equation: ……………………………………………………………………….

f) Complete the diagram above by filling the blanks in the spaces provided.

Activity 11

Answer the questions below.

13

WAJA F5 Chemistry 2010 Chapter 3 : Oxidation And Reduction1. Name three main ways to prevent rusting.

(i) …………………………………………………………………………………………………………….

(ii) …………………………………………………………………………………………………………….

(iii) ……………………………………………………………………………………………………………

2. Galvanising involves coating an iron or steel sheet with a thin layer of………………………………

3. Name three metals that can be used in sacrificial protection for an underground pipe.

(i) …………………………..….(ii) ……………..………………. (iii) …………………………………

4. Name a reagent that is usually used to detect the presence of iron(II) ion in an experiment to

investigate the rusting of iron.

………………………………………………………………………………………………..

Activity 121 Diagram below shows the apparatus set-up for the experiment to study the effect of metals P

and Q on the rusting of iron nail. The results are recorded after one day.

Test tube Metal Experiment After 1 day Observation

A Iron only

Some dark blue precipitate.

B Iron with metal P

Large amount of dark blue precipitate

C Iron with metal Q

No dark blue precipitate. Solution turns pink.

(a) Write the half-equation for the formation of iron(II) ion from iron.

.................................................................................................................................................(b) State the function of potassium hexacyanoferrate(III) solution in the experiment and

describe its change in colour if a positive result occurred.

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

……………………………………………………………………………………………………………

(c) Which test tube shows the highest rate of rusting of iron? Explain your answer.

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

14

WAJA F5 Chemistry 2010 Chapter 3 : Oxidation And Reduction..

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

...

(d) Arrange the metals Fe, P and Q in decreasing order of electrochemical series.

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

(e) (i) What happens to metal Q in test tube C?

….....................................................................................................................................

(ii) Suggest a metal that can be used as metal Q.

…....................................................................................................................................(f) State the ion that causes the solution in test tube C to turn pink.

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

C. THE REACTIVITY SERIES OF METALS WITH OXYGEN AND ITS APPLICATION

Learning Outcomes :You should be able to,

compare the differences in the vigour of the reactions of some metals with oxygen. deduce the reactivity series of metals. determine the position of carbon and hydrogen in the reactivity series of metals. state what the reactivity series of metals are. describe the extraction of iron and tin from their ores. explain the use of carbon as the main reducing agent in metal extraction. use the reactivity series of metals to predict possible reactions involving metals

Activity 131. Figure below shows the set-up of apparatus for an experiment to determine the order of

metals in the reactivity series. Solid potassium manganate (VII) is heated to release oxygen gas to react with hot metal powder.

The experiment is carried out using metal powders of copper, zinc, magnesium and lead . The observation of the experiments on the metal powders of copper, zinc, magnesium and lead in the experiments are shown in table below.

Type of metal ObservationCopper Faint glowZinc A bright flame spreads slowlyMagnesium A bright white shiny flame spreads quicklyLead Red hot and embers slowly

(a) Based on the observations in table above, arrange copper, zinc, magnesium and lead

15

WAJA F5 Chemistry 2010 Chapter 3 : Oxidation And Reductionin descending order of reactivity of metal towards oxygen.

Descending order of reactivity of metals with oxygen.

(b) Name two other substances that can be used to produce oxygen gas in the experiment (i) ………………………………………………

(ii) ………………………………………………

(c) Write a balance chemical equation for each of the reaction below.

(i) Copper + oxygen

…………………………………………………………………………………………..

(ii) Zinc + oxygen

……………………………………………………………………………………………

(iii) Magnesium + oxygen

……………………………………………………………………………………………(iv) Lead + oxygen

……………………………………………………………………………………………

2) According to the chemical equation below, carbon reacts with oxygen to produce ……………

………………………….. gas.

C ( s ) + O2 (s ) → CO2 ( g )

3) Based on the reactivity series of metals with oxygen, carbon able to displace a …………… ……………….. metal from its metal oxide. Thus, by heating a mixture of metal

oxide and carbon , the reactivity of carbon can be determined.

0 Oxidation +4

C ( s ) + 2PbO (s ) → CO2 ( g ) + 2Pb(s) +2 Reduction 0

4) Carbon is ………………… to carbon dioxide and lead (II) oxide is reduced to lead. 5) Carbon acts as a (i)…………………………….. agent which displaces a metal from its oxide

while the metal oxide is the (ii) …………………….agent.

6) Carbon is not able to displace a …………… ………………. metal from its metal oxide. Hence,

there is no displacement reaction when a mixture of magnesium oxide and carbon is heated.

7) Carbon is positioned in between (i) …………………………and (ii) …………….. in the reactivity 16

WAJA F5 Chemistry 2010 Chapter 3 : Oxidation And Reductionseries.

8) Oxides of metals W,X, Y, Z are heated with equal amount of carbon powder in an experiment to compare their reactivity with carbon. The changes observed are recorded in the table below.

Mixture ObservationCarbon + oxide of W No change

Carbon + oxide of X Dim glow. Grey residue is formed

Carbon + oxide of Y No change

Carbon + oxide of Z Bright glow. Brown residue is formed (a) Based on the observation , classify the metals in groups that are

(i) more reactive than carbon: …………………………………………………………………

(ii) less reactive than carbon: …………………………………………………………………

(b) Suggest a possible element for metals X and Z

X : …………………………………… Z : …………………………………………. (c) The reactivity of W and Y can be compared by heating an equal amount of W powder

with oxide of Y in a crucible using the same apparatus set-up.

(i) What is the expected observation if W is more reactive than Y? Explain your answer

……………………… ………………………………………………………………………

………………………………………………………………………………………………… (ii) Suggest the possible elements for W and Y

W : ………………………………… Y : ………………………………………………..

(iii) Write a balanced chemical equation for the reaction between W (charge of +2) and oxide of Y (charge of +3).

…………………….. …………………………………………………………………..

(iv) Identify the reducing agent and oxidising agent in the reaction between W and oxide of Y.

Reducing agent: ………………..……… Oxidising agent: ……………………………

17

WAJA F5 Chemistry 2010 Chapter 3 : Oxidation And Reduction9. Complete the reactivity series of metals with oxygen given below by writing the name of the

missing elements in the spaces provided.

Reactivity decreases

10. The following shows part of the increasing order of reactivity series of metals with oxygen.

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

Insert the positions of carbon and hydrogen in the above series by using arrows to indicate its position.

11. Predict what will be observed when,(a) hydrogen gas is heated with copper (II) oxide in tube.

……………………..…………………………………………………………………………............

…………………….…………………………………………………………………………………. (b) a piece of burning magnesium ribbon is dropped into a gas jar filled with carbon dioxide.

……..……………………………………………………………………..……………………………

…………………………………..…………………………………………………………………….

(c) carbon is heated with magnesium oxide.

…………………………………………………………………………………………....................

12. Complete the following table by giving the main mineral in ore and the metal extracted from its ore.

Ore Main mineral in ore Metal extractedName Formula

(a) Bauxite

(b) Hematite

(c) Magnetite

(d) Cassiterite

18

Potassium

Calcium

Aluminium IronTin

Mercury

Gold


D. ELECTROLYTIC AND CHEMICAL CELLS

Learning Outcomes :You should be able to, explain with examples the oxidation and reduction reactions at the electrodes of various chemical cells. explain with examples the oxidation and reduction reactions at the electrodes of various electrolytic cells. state the differences between electrolytic and chemical cells in terms of basic structure, energy conversion

and the transfer of electrons at the electrodes . compare and contrast electrolytic and chemical cells with reference to the oxidation and reduction process.

Activity 14

1) Below are listed the differences between electrolytic and chemical cells. Complete the statements by filling in the blanks with the correct words.

19

It requires a source of

…………………………………….

The electrodes may be of the …………

material such as …………………

The electrical energy

causes …………………… reactions

to occur at electrodes.

Electrons flow from the …………….

electrode (anode) to the …………….

electrode (cathode) through the

…………………. (external circuit)

It does not require a source of

……………………………………

The electrodes must be of

two …………………...... metals.

The chemical reactions that occur at

the electrodes produce

an ………………………………………

Electrons flow from the more

………………. metal ……………

terminal) to the less …………………

metal (……………………. terminal)


2) The figure above shows the electrolysis process of molten lead (II) bromide. Answer the questions below.(a) State the ions contain in the molten lead (II) bromide. ………………………………………….

(b) Pb2+ ions move to the (i) ……………………. while Br ions move to the (ii) ……………………

(c) Br ions act as the (i) ……………………. agent, losing electrons at the electrode to become

(ii) …………………… molecules. Thus, Br ions undergo (iii) ……………………….. .

(d) Oxidation half-equation: …………………………………………………….

(e) Pb2+ ions act as the (i) ……………………. … agent, accepting electrons to become

(ii) ……………………….. metal. Thus, Pb2+ ions undergo (iii) ……..……….. .

(f) Reduction half-equation : …………………………………………………...

3) Figure below shows a chemical (voltaic) cell.

a) Label the negative terminal and positive terminal and show the direction of the flow of electrons by using arrows the above figure.

b) Write the half-equation for the reaction at the positive terminal.

…………………………………………………………………………………………………...

c) Write the half-equation for the reaction at the negative terminal.

…………………………………………………………………………………...............

d) State the substance that undergoes oxidation.

…………………………………………………………………………………………………...

20

WAJA F5 Chemistry 2010 Chapter 3 : Oxidation And Reductione) State the substance that undergoes reduction.

…………………………………………………………………………………………………...

4) Similarities and differences of the redox reactions in electrolytic cell and a voltaic (chemical) cell

SimilaritiesIn both cells, electrons are transferred from the …………… agent to the ……………… agent. oxidation occurs at the anode.

…………………… occurs at the cathode

Differences

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Electrolytic cell Chemical cell

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