REVISIONELECTROCHEMISTRY

OXIDATIONis a loss of electrons

An increase in oxidation number

REDUCTIONis a gain of electrons

A decrease in oxidation number

CATHODEThe electrode where reduction takes place

ANODEThe electrode where oxidation takes place

ELECTROLYTEsolution/liquid/dissolved substance that conducts

electricity through the movement of ions.

TABLE OF STANDARD REDUCTION POTENTIALS

STANDARD CONDITIONS

• C• 25• Pressure of 1atm (101,3 kPa)• Metal electrodes• When a half-cell consists of a gas, Pt is used to

provide the surface area for the reaction

2

2

The two equations represent the halfreactions that

occur in an electrochemical cell.

Pt + 2e Pt E = + 1.20V

Sr + 2e Sr E = -2.89V

Which one of the follow

2 2

ing is TRUE when the cell is

working?

The mass of the Sr electrode will decrease.

B Pt oxidizes easier than Sr

C Pt reduces easier than Sr .

D In the external circuit, electrones will flow from

t

C

he P

A

t-electrode to the Sr-electrode

GALVANIC CELL

a cell in which chemical energy is converted into electrical energy.

A galvanic (voltaic) cell has self-sustaining electrode reactions

SPONTATEOUS REACTIONS

CELL POTENTIALS• Driving force of a cell to make electrons move -

away from the anode to the cathode.• . • = -• =reduction-oxidation

CELL NOTATION

• The H2|H+ half-cell is treated just like any other half-cell. . • Cell terminals (electrodes) are written on the outside of the cell

notation.

• Active electrodes reducing agent | oxidised species || oxidising agent | reduced species

• Inert electrodes (usually Pt or C): Pt | reducing agent | oxidised species || oxidising agent | reduced species | Pt

Example: Pt | Cℓ-(aq) |Cℓ2(g) || F2(g) | F-(aq) | Pt

SALT BRIDGE

Its function is to maintain ELECTRICALneutrality

During an experiment the following magnesium-lead electrochemical cell is built.

Both half cells contain nitrate salt solutions. M en N represent electrodes

stel elektrodes voor. A lamp wick drenched in

an electrolyte is used as a salt bridge

Write down the values of the standard conditions

Which electrode is the anode - give a reason for your answer

Write down the half reaction that occurs at elect

a

b

c

rode N

Write the cell notation for this cell

Calculate the emf of the cell when it is working

The lamp wick is now replaced with a convensional salt bridge (glass tube)

Does this change the emf of the

d

e

f cell? Explain

0 0

2

2 2

0

M is the anode, because electrons are flowing away form M

Mg is the anode, because Mg is being oxidised

Pb ( ) 2 '

Mg | ( )|| | ( )

, the

0.13 2.

e

36

2.2

f

3

m

sel katode anodeE

b

c aq e Pb s

d s Mg aq Pb aq Pb s

e

f o

E

N

E

V

is only dependent on the concentration of the reactants

 Magnesium is used to protect underground iron pipes against rusting.

The diagram below shows an iron pipe connected to a magnesium bar.

Use the Table of Standard Reduction Potentials to explaina why

m

agnesium can be used to protect an iron pipe against rusting

 The iron pipe in contact with the magnesium bar forms an electrochemical

cell. What serves as the salt bridge of this cell?

Give a r

b

c eason

why the magnesium bar must be replaced after some time

Write down a half-reaction to support your answerd to c

2

2

is a stronger reducing agent than

grondwater

magnesium plate is the anode and will

be oxidised.

oxidised to ( )

Mg ( ) 2 '

a Mg Fe

b The

c The

Mg s is Mg aq

d s Mg aq e

ELECTROLYTIC CELLa cell in which electrical energy is converted into

chemical energy.

ELECTROLYSISThe chemical process in which electrical energy is converted to

chemical energy OR

the use of electrical energy to produce a chemical change.

ELECTROLYTIC CELL

ELECTROPLATING

An attractive silver appearance can be created by electroplating artefacts made from cheaper

metals, such as nickel, with silver. The simplified diagram below represents an arrangement that

can be use

d to electroplate a nickel artefact with silver. 

Which electrode cathode/anode will the nickel artefact represent?

Name the metal represented by electrode Y

Write down the half-reaction responsib

a

b

c le f

or the change that occurs at the surface of the artefact

 In industry some plastic articles are sometimes electroplated.

Explain why plastic must be coated with graphite before electropl

d

ating

ELECTROPLATING

Ag ( ) 1 '

cells needs electrodes that

are made form METAL

a cathode

b Silver

c aq e Ag s

d Elektrochemical

REFINING OF COPPER

 Electrolysis is an important industrial process used to decompose compounds, extract metals

from their ores and to purify metals like gold or copper. The simplified diagram below

represents an electr

olytic cell used to purify copper. 

Define the term electrolysis

 hich electrode, P or Q, consists of the impure copper?

Explain how you arrived at your answer.

Write down the half-reaction that t

a

b

c akes

place at electrode Q

During purification, metals such as silver and platinum form sludge at the bottom of the

container. Refer to the relative strengths of reducing agents to explain why these

d

two

me

tals do not form ions during the purification process.

 Explain why the concentration of the copper II sulphate solution remains constant.

Assume that the only impurities in the copper are silver

d

and platinum

REFINING OF COPPER

2

,

the anode consists of the impure copper

- it is the electrode that is connected to the positive terminal

of the battery

Cu 2 '

Cu-ions are reduced when it plates the cathode

Cu-ions are strong

a P

c aq e Cu s

d

2

oxidising agents.

The other metals (Ag and Pt) are strong redusing agents

and will therefore oxidise easily

The oxidation half reaction at the anode produces

at the same rate as the reduction

d Cu ions

2 half reaction 'used' the Cu ions

CHLOOR-ALKALI INDUSTRIE

RECOVERY OF ALUMINIUM