Mastering IGCSE Chemistry: The Essential Guide to Acids, Bases, and Salts (2025-26 Edition)

STUDY REFERENCE: IGCSE CHEMISTRY (0620)
UNIT: ACIDS, BASES, AND SALTS (2025-26 SYLLABUS)


1. CORE DEFINITIONS

●​ Acids: Proton (H+) donors. In water, they produce H+ ions.
●​ Bases: Proton (H+) acceptors.
●​ Alkalis: Bases that are soluble in water; they produce Hydroxide (OH-) ions.
●​ Strong vs. Weak:
○​ Strong: Completely ionised in aqueous solution (e.g., Hydrochloric Acid,
Sulfuric Acid).
○​ Weak: Only partially ionised in aqueous solution (e.g., Ethanoic Acid, Citric
Acid).


2. THE FOUR ESSENTIAL CHEMICAL REACTIONS

1.​ Acid + Metal -> Salt + Hydrogen (H2)
2.​ Acid + Base (Neutralisation) -> Salt + Water (H2O)
3.​ Acid + Metal Carbonate -> Salt + Water + Carbon Dioxide (CO2)
4.​ Acid + Ammonia -> Ammonium Salt (Note: No water is produced here).

3. SALT PREPARATION METHODS (PRACTICAL REFERENCE)

●​ Method 1: Titration (Soluble Base + Acid)
○​ Used for: Group 1 (Sodium, Potassium) and Ammonium salts.
○​ Process: Use a pipette/burette with an indicator to find the end-point.
Repeat without indicator to get a pure solution.
●​ Method 2: Excess Solid (Insoluble Base/Metal + Acid)
○​ Used for: Most soluble salts (e.g., Copper(II) Sulfate).
○​ Process: Add solid until no more dissolves -> Filter -> Heat filtrate to
saturation -> Crystallise.
●​ Method 3: Precipitation (Two Soluble Salts)