Redox reactions: WAEC Chemistry Past Questions and Answers

What the WAEC syllabus covers in Redox reactions

Our summary: Oxidation and reduction, balancing redox equations, electrochemical cells, electrolysis and corrosion.

• Oxidation and reduction process ((1) Oxidation and reduction in terms of: (a) addition and removal of oxygen and hydrogen; (b) loss and gain of electrons; (c) change in oxidation numbers/states. (2) Determination of oxidation numbers/states.)
• Oxidizing and reducing agents ((1) Description of oxidizing and reducing agents in terms of: (a) addition and removal of oxygen and hydrogen; (b) loss and gain of electrons; (c) change in oxidation numbers/state.)
• Redox equations (Balancing redox equations by: (a) ion, electron or change in oxidation number/states; (b) half reactions and overall reaction.)
• Electrochemical cells (Definition/explanation.)
• Electrochemical cells: standard electrode potential ((1) Standard hydrogen electrode: meaning of standard electrode potential (E°) and its measurement. (2) Only metal/metal ion systems should be used.)
• Electrochemical cells: drawing of cell diagram and writing cell notation
• Electrochemical cells: e.m.f. of cells ((1) Electrochemical cells as a combination of two half-cells. (2) The meaning of magnitude and sign of the e.m.f.)
• Electrochemical cells: application of electrochemical cells ((1) Distinction between primary and secondary cells. (2) Daniell cell, lead acid battery cell, dry cells, fuel cells and their use as generators of electrical energy from chemical reactions.)
• Electrolysis (Definition.)
• Electrolysis: electrolytic cells (Comparison of electrolytic and electrochemical cells; weak and strong electrolyte.)
• Electrolysis: principles of electrolysis (Mechanism of electrolysis.)
• Electrolysis: factors influencing discharge of species (Limit electrolytes to molten PbBr₂ and NaCl, dilute NaCl solution, concentrated NaCl solution, CuSO₄(aq), dilute H₂SO₄, NaOH(aq) and CaCl₂(aq) (using platinum or graphite and copper electrodes).)
• Electrolysis: Faraday's laws (Simple calculations based on the relation 1 F = 96,500 C and mole ratios to determine mass, volume of gases, number of entities, charges etc. using half and overall reactions.)
• Electrolysis: practical application (Electroplating, extraction and purification of metals.)
• Corrosion of metals ((1) Corrosion treated as a redox process. (2) Rusting of iron and its economic costs. (3) Prevention based on relative magnitude of electrode potentials and preventive methods like galvanizing, sacrificial/cathodic protection and non-redox methods (painting, greasing/oiling etc.).)

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