Chemistry, C6B_Chemical Cell (S)

8/8/2019 Chemistry, C6B_Chemical Cell (S)

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4541 CHEMISTRY Chapter 6

C Analysing Voltaic Cell // Chemical Cell

A chemical cell that produces electrical energy when chemical reactions occur in it.

(I) Simple cell

1. Produced when two different metals are immersed in an electrolyte and are connected by an

external circuit.

2. The voltage of chemical cell depends on the distance between the two metals in the

Electrochemical Series :

the further the distance between them, the higher is the voltage.

Example :

Simple cell using magnesium and copper strips as electrodes and copper(II) sulphate

solution as electrolyte.

Chapter 6 Electrochemistry31

Position of magnesium is higher than

copper in the Electrochemistry Series.

A magnesium atom release electrons more

easily than a copper atom.

Mg → Mg2+ + 2e

The Mg2+ ions are released into the CuSO4

solution while the electrons that are released

flow through the external circuit toward the

copper plate.

At the copper electrode, the electrons are

accepted by the Cu2+ ions.

Cu2+ + 2e → Cu

The copper atoms are formed.

Brown solid is deposited at cathode.Cathode becomes thicker. The size of the

cathode becomes bigger. The mass of the

cathode increases.

Magnesium Copper

Copper(II)

sulphate

solution

Electron flowElectron flow

Electrical current produced is detected by

the voltmeter/galvanometer

[Chemical energy→ Electrical energy]

Positive terminal :

Less electropositive metal.

The electrons that flow from the

external circuit are received by the

positive ion in the electrolyte

through this terminal.

Metallic ion becomes metal atom

(becomes thicker).

Negative terminal :

More electropositive metal.

Metal atom will release electrons

that will flow through the external

circuit.

Metal atom becomes metallic ion

(becomes thinner).

v

+-




Activity 15 :-

(a) For all voltaic cells / chemical cells below :

(i) mark the positive and negative terminal.

(ii) draw arrows (

) to show the direction of the electrons flow.

(b) Which cell produced the highest voltage value? Explain why.

………………………………………………………………………………………………

………………………………………………………………………………………………


Silver plate

Silver nitratesolution

Magnesiumribbon

Zinc plateSilver plate

Cell A Cell B

Copper plate

Copper(II) sulphatesolution

Magnesium

ribbonZinc plateCopper

plate

Cell C Cell D

Copper plate

Silver plateZinc plateMagnesium

ribbon

? ?

Cell E Cell F

V1

V2

V3

V4

V5

V6




(II) Daniell cell

(a) Zn Zn2+ Cu2+ Cu cell

(a) Zinc electrode :

(i) …………… terminal because ……………………………………………………………..

(ii) Equation : ……………………………………………………………………………….

(iii) Observation : ………………………………………………………………………………

(b) Copper electrode :

…………… terminal because …………………………………………………………….

Equation : ………………………………………………………………………………..

) Observation : ………………………………………………………………………………

If the zinc metal is replaced with a magnesium metal, the voltage reading increases

because magnesium is further from copper in the Electrochemical Series.

OR

If the copper metal is replaced with a silver metal, the voltage reading increases

because silver is further from zinc in the Electrochemical Series.


Zinc

sulphate

solution

Copper(II)

sulphate

solution

Zinc

Dilute

sulphuric

acid

Copper

Voltage / V

Mg

Zn

Cu

Ag

V1

V2

V3

V2

V1…….

V3

V1…….




Activity 16 :-

State the advantages and disadvantages of the cell in the table given below.

Types of cell Advantages Disadvantages

1. Lead – acid

accumulator

2. Dry cell

3. Mercury cell

4. Alkaline cell

5. Nickel- cadminium cell





Activity 17 :-

1 (a) Draw a labelled diagram to show the similarities and differences between an electrolytic and

a voltaic cell.[Using copper plates, magnesium ribbon, copper(II) sulphate solution as materials]

(b) The similarities between an electrolytic cell and a voltaic cell.

(i) They consist of an ……………………………………….. each.

(ii) They consist of two ………………………………………. each.

(iii) The process of donation of electrons occurs at the ………………………………………

while the process of acceptance of electrons occurs at the ………………………………


Electrolytic cell Voltaic cell




Convert electrical energy to

…………………..

Electrical energy produceschemical reaction.

Energy conversion Convert chemical energy to

…………………..

Chemical reactions produceelectrical energy.

Current supply into the cell Current Current produced by the cell

(a) The anode is

………………….. charged.

(b) The cathode is

………………….. charged.

Charge of :

(a) anode

(b) cathode

(a) The anode is

………………….. charged.

(b) The cathode is

………………….. charged.

Electrons flow from the

………………….. to the

………………….. through the

external circuit.

Electrons flow Electrons flow from the

………………….. to the

………………….. through the

external circuit.

(a) ………………….. of

electrons. (Oxidation)

Anion gives out electrons

to anode.(b) ………………….. of

electrons. ( Reduction)

Cation accept electrons

from negative terminal.

Types of reaction that

takes place at the :

(a) positive terminal

(b) negative terminal

(a) ………………….. of

electrons. ( Reduction)

Electrons receive by

positive terminal.(b) ………………….. of

electrons. (Oxidation)

Electrons given out from

negative terminal.

Pair of carbon (graphite),

platinum or

pair of ………………… metals.Types of electrodes Two of ……………… metals.


An Electrolytic cell A Voltaic cell

Differences




Activity 18 :-

The diagram below shows two types of cell.

.

Compare and contrast cell X and cell Y.

Answer :

Cell X Cell Y

Type of cell ………………….. cell. ………………….. cell.

Conversion of

energy

………………….. energy to

………………….. energy.

………………….. energy to

………………….. energy.

Type of

electrodes

Positive terminal/Anode :

…………………..

Negative terminal/Cathode :

…………………..

Positive terminal/ Cathode :

…………………..

Negative terminal/ Anode :

…………………..

Ions in

electrolyte

Cation : …………………..

Anion : …………………..

Cation : …………………..

Anion : …………………..


Copper plate

Copper(II) sulphate

solution

Copper plate

Magnesium

ribbonP Q R S

Cell X Cell Y




Observations


………………………………………..

………………………………………..


……………………………………….

………………………………………..

N egative terminal/Cathode :

………………………………………..

………………………………………..

Negative terminal/Anode :

………………………………………..

………………………………………..

Half equations


……………………………


……………………………

Negative terminal/Cathode :

……………………………

Negative terminal/Anode :

……………………………


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Chemistry, C6B_Chemical Cell (S)