Ionic Half Equations (Cambridge (CIE) O Level Chemistry): Revision Note

Ionic Half Equations

• In electrochemistry we are mostly concerned with the transfer of electrons, hence the definitions of oxidation and reduction are applied in terms of electron loss or gain rather than the addition or removal of oxygen

• Oxidation is when a substance loses electrons and reduction is when a substance gains electrons

• As the ions come into contact with the electrode, electrons are either lost or gained and they form neutral substances

• These are then discharged as products at the electrodes

• At the anode, negatively charged ions lose electrons and are thus oxidised

• At the cathode, the positively charged ions gain electrons and are thus reduced

• Ionic half equations show the oxidation and reduction of the ions involved

• It is important to make sure the charges are balanced 

Table of Reduction and Oxidation Reactions at the Electrodes