Monday 31 July 2023

IGCSE - Electrochemistry (Conductivity, Electrolysis, Electroplating) ppt presentation



IGCSE Chemistry


  • Describe metals as electrical conductors and nonmetallic materials as non conducting insulator

  • Define electrolysis and identify the components of an electrolytic cell

  • Describe and predict the electrolysis products of binary compounds in molten state

  • Describe the electrolysis of concentrated sodium chloride and dilute sulfuric acid using inert electrodes.

  • Describe how to electroplate a metal object.

  • State that a hydrogen-oxygen fuel cell generates electricity.

Types of electrical conductivity

Conductivity in solids

Conductivity is a measure of the ability of materials to pass an electrical current

If the light bulb lights up, it means that the material being tested is an electrical conductor

Materials conduct electricity because they contain charged particles that can move around in them.

In solids these charged particles are called ELECTRONS.

Electrons are tiny negatively charged particles.

In some materials the electrons can wander about between the atoms, these electrons are called FREE ELECTRONS. The more free electrons there are in a solid the better it will conduct electricity.

  • If we now think of the metal as a wire as shown in the diagram then the tiny electrons show no particular direction of movement (Figure 1(a)).

  • But if we now connect a battery to the two ends of the wire the electrons drift down the wire in one direction (Figure 1(b)).

Conductivity in liquids

Some liquids conduct electricity. 

The process in which an electric current flows through a liquid compound or solution is called electrolysis.

Unlike in liquid compounds or solutions produces a chemical reaction. 

Liquids that conducts electricity by the movement of ions are called electrolytes

Liquid that do not conduct electricity are called non-electrolytes. They do not contain ions.

Properties of electrolytes and non-electrolytes


  • An electrolyte is a chemical compound which conduct electric current in a molten  state or an aqueous solution and undergoes chemical changes

  • Electrolytes contain ions which move about freely to carry electric charge

  • An electrolyte can break down into its element at electrodes when an electric current flows through it.

  • Electrolytes: molten aluminum oxide, molten lead(ii) chloride, base solution, acid solutions

Properties of electrolytes and non-electrolytes


  • A non electrolyte is a chemical compound which can not conduct electric current in all states.

  • There will be no change on a non-electrolyte when an electric current flows through it. 

  • Non electrolyte are made from molecules only. There are no ions which can carry electrical charges in non-electrolyte. 

  • Covalent compounds: sugar, sulphur, benzene, alcohol, naphthalene.

Difference between conductivity in solids and electrolytes (liquids)

Conductivity in metals:

  • Electrons flow

  • A property of elements (metals and carbon as graphite) and alloys

  • Takes place in solids and liquids

  • No chemical change takes place

Electrolytic conductivity

  • Ions flow

  • A property of ionic compounds

  • Takes place in liquids and solutions (not solids)

  • Chemical decomposition takes place.


  • Electrolysis is the process of electrically inducing chemical changes in a conducting melt or solution e.g. splitting an ionic compound into the metal and non-metal.

  • The electric current enters and leaves the electrolyte through electrodes

  • Cathode (negative electrode) which attract cations

  • Anode (positive electrode) which attract anions

Electrolysis of molten compound

  • When a molten ionic compound is electrolysed, the metal is produced at cathode and the non-metal is produced at the anode

     When switch is closed and circuit is complete, the current flows and bromine vapour (red-brown) begins to bubble off the cell has caused a chemical change (decomposition). The cell decomposes the molten lead(ii) bromide because Pb2+ and Br- ions present move to opposite electrodes where they are discharged.

Electrolysis of molten compound

  • During electrolysis, the lead ions (Pb2+) move to the cathode, each lead ion picks up (accepts/gain) two electrons and become a lead atom. (discharging)

cathode (-)

Pb2+  (l)  +   2e    →    Pb  (l)    reduction

  • The bromide ions (Br-) move to the anode. Each bromide ion gives up (donates) one electron to become a bromine atom: Br-    → Br  + e

     Then two bromine atoms bonds (joins) together to make a bromine molecule.

anode (+)

2Br- (l)  →  Br2 (g)     +    2e    oxidation 

Electrolysis of molten compound

  • Ex. Electrolysis of molten NaCl

cathode (-)

Na+  (l)  +   e    →    Na  (l)    reduction

anode (+)

2Cl- (l)  →  Cl2 (g)     +    2e    oxidation   


  • Write the ionic equation at the electrodes for the following molten compound:

  1. Lead(II) fluoride

  2. Aluminum oxide

  3. Potassium chloride

Electrolysis of aqueous solution

  • In aqueous solution, there are four kinds of ions:

two come from the electrolytes

two come from water ( H+ and OH-)

E.g. Concentrated NaCl(aq) : Na+, Cl-, H+, OH-  (ions present)

cathode (-)

reduction:  2H+(aq)   +  2e   →   H2 (g)


oxidation: 2Cl-(aq) →  Cl2(g)     +   2e 

as H+ and Cl- are discharged, Na+ and OH- remain in the solution become NaOH solution

Selective discharged of ions

  • At Cathode:

~ H+ (aq) and ions of less reactive metals (Cu2+ (aq), Ag+(aq) are discharged

~ if the cations are ions of reactive metals, the ions are not dicharged in the presence of water. but H+ from water are discharged to form H2 gas

2H+   +  2e  →  H2(g)

Li > K > Sr > Ca > Na > Mg > Al > Zn > Cr > Fe > Cd > Co > Ni > Sn > Pb > H > Cu > Ag > Hg > Pt > Au

Selective discharged of ions

At Cathode:

  • The more reactive metal, the more it tends to stay as ions and not be discharged. The H+ ions will accept electrons instead. Hydrogen molecules will be formed, leaving the ions of the reactive metal in the solution.

2H+   +  2e  →  H2(g)

  • In contrast, the ions of less reactive metals (e.g. Cu2+ ions) will accept electrons readily to form metal atoms. In this case, the metal will be discharged, leaving the H+ ions in the solution.

Li > K > Sr > Ca > Na > Mg > Al > Zn > Cr > Fe > Cd > Co > Ni > Sn > Pb > H > Cu > Ag > Hg > Pt > Au

  • At Anode

~If the ions of a halogen (halides: F-, Cl-, Br-, I-) are present in a high enough concentration (concentrated), they will give up electrons more readily than OH- ions will. Molecules of fluorine, chlorine, bromine or iodine are formed. The OH- ions remain in solution.

~If no halides are present, or halides solution is too dilute, the OH- ions will give up electrons (discharged) to form oxygen. Sulfate and nitrate ions are not discharged in presence to OH- ions.

4OH- (aq)  →   O2(g)   +   2H2O(l)  + 4e

Electrolysis of copper(ii) sulfate with copper electrodes

It is possible to use electrodes other than graphite or platinum; electrodes that are not inert. E.g. a cell can be set up to electrolyse copper(ii) sulfate solution using copper electrodes. 

As electrolysis takes place, the cathode gains mass as copper is deposited on the electrode:

At cathode:  Cu2+ (aq)  +  2e  →  Cu(s)

The anode, however, loses mass as copper dissolves from the electrode:

At the anode Cu(s) →  Cu2+(aq)  +  2e

The electrolysis of copper(ii) sulfate using copper electrodes. The movement of ions effectively transfer copper from anode to cathode. 

The color of copper(ii) sulfate solution does not change because the concentration of the Cu2+ ions in the solution remains the same.

The idea of dissolving anodes is useful in the process of electroplating and in the purification of copper


Electroplating is the process of coating a metal with a thin layer of another metal by electrolysis to improve the metal's corrosion resistance, improve the appearance of metal object.

The cathode is the object to be plated (coated)

The anode is made from metal being used to plate (coat) the object.

The electrolyte is a salt of the same metal as used for the anode.

As the process proceeds, the anode dissolves away into the solution, replacing the metal plated on to the object. As a result of metal ions moving into solution at the anode the concentration, and any colour, of the solution remains the same throughout the electrolysis.


E.g. We are going to plate an iron spoon with copper.

Anode: Copper rod

Cathode: iron spoon

Electrolyte: Copper sulfate solution/copper nitrate solution

As electrolysis takes place, the cathode (object/iron spoon) gains mass, where it is coated with copper. Copper is deposited at cathode.

At cathode:  Cu2+ (aq)  +  2e  →  Cu(s)

The anode, however, loses mass as copper rod dissolves from the electrode:

At the anode Cu(s) →  Cu2+(aq)  +  2e

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