Acids, bases and salts: NECO Chemistry Past Questions and Answers

What the WAEC syllabus covers in Acids, bases and salts

Our summary: What acids, bases and salts are, how strong they are, the pH scale, indicators, salt hydrolysis and acid-base titration.

• Definitions of acids and bases ((1) Arrhenius concepts of acids and bases in terms of H₃O⁺ and OH⁻ ions in water. (2) Effects of acids and bases on indicators, metal Zn, Fe and trioxocarbonate (IV) salts and hydrogentrioxocarbonate (IV) salts.)
• Physical and chemical properties of acids and bases (Characteristic properties of acids and bases in aqueous solution to include: (a) conductivities, taste, litmus/indicators, feel etc.; (b) balanced chemical equations of all reactions.)
• Acids, bases and salts as electrolytes (Electrolytes and non-electrolytes; strong and weak electrolytes. Evidence from conductivity and enthalpy of neutralization.)
• Classification of acids and bases ((1) Strength of acids and bases. (2) Classify acids and bases into strong and weak. (3) Extent of dissociation reaction with water and conductivity. (4) Behaviour of weak acids and weak bases in water as example of equilibrium systems.)
• Concept of pH ((1) Definition of pH and knowledge of pH scale. (2) Measurement of pH of solutions using pH meter, colorimetric methods or universal indicator. (3) Significance of pH values in everyday life e.g. acid rain, pH of soil, blood, urine.)
• Salts (Meaning of salts. Types of salts: normal, acidic, basic, double and complex salts.)
• Salts: laboratory and industrial preparation of salts; uses ((1) Description of laboratory and industrial production of salts. (2) Mining of impure sodium chloride and conversion into granulated salt. (3) Preparation of NaOH, Cl₂ and H₂.)
• Salts: hydrolysis of salt ((1) Explanation of how salts form acidic, alkaline and neutral aqueous solutions. (2) Behaviour of some salts (e.g. NH₄Cl, AlCl₃, Na₂CO₃, CH₃COONa) in water as examples of equilibrium systems. (3) Effects of charge density of some cations and anions on the hydrolysis of their aqueous solution. Examples to be taken from group 1, group 2, group 3 and the d-block element.)
• Deliquescent, efflorescent and hygroscopic compound (Use of hygroscopic compounds as drying agent should be emphasized.)
• Acid-base indicators ((1) Qualitative description of how acid-base indicator works. (2) Indicators as weak organic acids or bases (organic dyes). (3) Colour of indicator at any pH dependent on relative amounts of acid and base forms. (4) Working pH ranges of methyl orange and phenolphthalein.)
• Acid-base titration ((1) Knowledge and correct use of relevant apparatus. (2) Knowledge of how acid-base indicators work in titrations. (3) Acid-base titration experiments involving HCl, HNO₃, H₂SO₄ and NaOH, KOH, Ca(OH)₂, CO₃²⁻, HCO₃⁻. (4) Titration involving weak acids versus strong bases, strong acids versus weak bases and strong acids versus strong bases using the appropriate indicators and their applications in quantitative determination; e.g. concentrations, mole ratio, purity, water of crystallization and composition.)

Syllabus content © The West African Examinations Council (WASSCE (harmonised West African syllabus)). NECO questions are matched to the WAEC syllabus topic.