Cambridge IGCSE Chemistry (0620 & 0971) Comprehensive Study & Practical Guide: Key chemical concepts, stoichiometry, qualitative analysis identification tables, and exam success strategies by Dr. Khaled Dabour (DABOURHUB Academy).
1. Core Principles: Atomic Structure, Bonding & The Periodic Table
Matter is composed of atoms containing protons (+1 charge), neutrons (neutral), and electrons (-1 charge). Elements are organized in the Periodic Table by atomic number. Group I alkali metals exhibit increasing reactivity down the group, while Group VII halogens exhibit decreasing reactivity. Ionic bonding occurs between metals and non-metals via electron transfer, whereas covalent bonding involves sharing electron pairs between non-metal atoms.
2. Stoichiometry & Quantitative Chemistry Calculations
Mastering mole calculations is essential for Paper 2, Paper 4, and Paper 6:
- Number of Moles (solids): Moles = Mass (g) ÷ Molar Mass (g/mol).
- Number of Moles (solutions): Moles = Concentration (mol/dm³) × Volume (dm³). Note: Convert cm³ to dm³ by dividing by 1000.
- Molar Gas Volume: 1 mole of any gas occupies 24.0 dm³ (24,000 cm³) at room temperature and pressure (r.t.p.).
- Empirical Formula Determination: Divide percentage/mass of each element by its Ar, divide results by the smallest quotient to obtain the simplest integer ratio.
3. Qualitative Analysis: Identification of Cations and Anions
Memorizing the characteristic precipitate colors and solubility in excess reagent is mandatory for Paper 6:
| Ion | Effect of Aqueous Sodium Hydroxide (NaOH) | Effect of Aqueous Ammonia (NH₃) |
|---|---|---|
| Copper(II) (Cu²⁺) | Light blue precipitate; insoluble in excess | Light blue precipitate; dissolves in excess to give dark blue solution |
| Iron(II) (Fe²⁺) | Green precipitate; insoluble in excess; turns brown at surface | Green precipitate; insoluble in excess |
| Iron(III) (Fe³⁺) | Red-brown precipitate; insoluble in excess | Red-brown precipitate; insoluble in excess |
| Zinc (Zn²⁺) | White precipitate; dissolves in excess to give colorless solution | White precipitate; dissolves in excess to give colorless solution |
4. Acids, Bases & Salts Synthesis Techniques
Selecting the correct preparation method based on salt solubility:
- Titration: Soluble salt made from an acid and a soluble alkali/carbonate (e.g. NaCl from HCl + NaOH using methyl orange indicator).
- Excess Insoluble Base Method: Soluble salt made from an acid and an insoluble base/metal/carbonate (e.g. CuSO₄ from CuO + H₂SO₄; warm acid, add excess CuO, filter unreacted oxide, crystallize filtrate).
- Precipitation: Insoluble salt prepared by mixing two soluble aqueous solutions (e.g. BaSO₄ from BaCl₂ + Na₂SO₄; filter, wash precipitate with distilled water, dry in warm oven).