What is Electrochemistry?

Electrochemistry is the branch of chemistry that deals with the gain or loss of electrons during chemical reactions.

In electrochemistry, we talk about electrolytic cells and eletrochemical cells.

It is pertinent to mention that electrochemical cells convert chemical energy to electrical energy while electrolytic cells convert electrical energy to chemical energy.

I will start by explaining first the reactions and mechanism of operations in electrolytic cells.

Electrolytic cells and Electrolysis

First, Electrolysis is the chemical disintegration of an electrolyte (mainly ionic compound) by the passage of electricity.

Now, it is important to say that electrolytes could be classified as weak or strong electrolytes.

Strong electrolytes are ionic compounds that ionize completely in water while weak electrolytes are electrolytes that ionizes partially in water.

Examples of strong electrolytes are ionic compounds like NaCl, KCl and even strong acids and bases like concentrated HCl, NaOH etc.

Descriptions of Electrolytes

Electrolytes are described as molten , concentrated aqueous or dilute aqueous.

What I mean is that we can have Electrolytes in form of examples molten NaCl, Dilute aqueous NaCl and concentrated aqueous Electrolytes.

Mechanism  of Electrolysis

The mechanism of Electrolysis is best described using an electrolytic cells.

Electrolytic cell

The flow of electrons starts when a battery is switched on. The flow of electrons

Hint: The flow of electrons is contrary to the movement of electricity current.

The flow of electrons then moves to the cathode and enters into the electrolyte which could be in molten, dilute aqueous or concentrated aqueous form.

Electricity is carried from the cathode to the anode by the movement of mobile ions.

I always prefer explaining mechanism of electrolysis by the movement of electrons and not current because it is easier to understand from the point of electrons.

So electrons now move from anode back to the battery and then to the cathode thus completing the movement of electrons in the external circuit.

Additionally, to help explain this cell very well,  recall that there are two basic reactions that occur in electrolytic cell.

We have oxidation and reduction occurring in the cell.

Oxidation is loss of electrons and increase in oxidation number.

Reduction is the gain of and decrease in oxidation number.

We can use  Pneumonic OIL RIG to recall the definitions of the two terms.

What is Electrolysis and example?

In electrolysis, we need to understand two processes that take place.

There is migration of ions and preferential discharge of ions.

Migration of ions

During migration of ions, this happens when the battery is switched on and the electrons ( or current) starts moving.

There’s a rule in science and nature that unlike charges attract while like charges repel.

So positive ions migrate to negative electrode (cathode) while negative ions migrate to positive electrode (anode)

Then the second process is called the preferential discharge of ions.

Preferential discharge of ions

Here, there isca need to neutron that there are three factors that affect the discharge of ions.

3 Factors that affect discharge of ions

  1. Position of ion in the electrochemical series
  2. Concentration of ions
  3. Nature of electrodes

Please, let me briefly hint on these factors for few minutes.

1, Position of ion in the electrochemical series

The rule is that ions lower in the series is usually discharged

2, Concentration of ions

Concentration of ions is a very important factor in electrolysis.  Usually the first three ions above hydrogen ion (H+) and hydroxide ion(OH) are discharged.

Hint: A concentrated solution is a solution with less water while a dilute solution is a solution with excess water.

3, Nature of Electrodes

Another factor considered is the nature of electrodes.

We have inert (unreactive) and reactive electrodes.

Actually, to prevent interference of ions, we recommend you use inert electrodes.

Examples of electrolysis of common electrolyte.

A quick overview of Electrolysis and products at Cathode and anode

ElectrolyteProduct formed at anodeProduct formed at cathode
Dilute NaClOxygenHydrogen
Dilute CuCl2OxygenCopper
Molten PbBr2BromineLead
Concentrated CuSO4OxygenCopper
Molten NaClSodiumChlorine
Dilute Sulphuric acidHydrogenOxygen
Dilute hydrochloric acidHydrogenOxygen
Concentrated  Hydrochloric acid  HydrogenChlorine
Molten potassium BromidePotassiumBromine
Molten Aluminium oxideAluminiumOxygen
Concentrated NaClChlorineHydrogen

Electrolysis of Dilute aqueous solutions

Example 1

Electrolysis of Dilute aqueous NaCl

Recall the mechanism of electrolysis

We have two basic processes

Migration of ions

In dilute aqueous NaCl

NaCl==Na+ + Cl-

Discharge of ions

At Cathode ( Reduction)

Sodium ion  is reduced

Na+ + e-===Na

At Anode

Chloride ion is oxidised

Cl- – e-===Cl

Cl + Cl==Cl2

Example 2

Electrolysis of Dilute aqueous CuSO4

Discharge of ions


Copper is reduced

Cu2+ + 2e- ===Cu


4OH- ==2H2O + O2 + 4e’

Electrolysis of concentrated solutions

Electrolysis of concentrated Sodium Chloride (Brine)


Sodium ion is reduced

 Na+ +e- ===Na


Cl- – e-===Cl

Cl + Cl==Cl2

Electrolysis of concentrated Potassium  Chloride ( conc.KCl)


H+ + e-===H

H + H===H2


Cl- – e-===Cl

Cl + Cl==Cl2

Electrolysis of molten solutions

In molten solutions, there is competition for discharge  because no water present so the constituent ions are discharged.

Electrolysis of molten sodium chloride


Na÷ + e- ===Na


Cl- – e-===Cl

Cl + Cl==Cl2

Electrolysis of fused calcium chloride ( CaCl2)


Ca2+ + 2e-==Ca


Cl- – e-===Cl

Cl + Cl==Cl2

Electrolysis of molten Aluminium oxide


Al3+ +3e- ===Al



O + O==O2

O2===O2 ÷ 4e-

The study of electrochemistry is very important and makes our understanding of electrolysis and preferential discharge very easy.

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