IGCSE Chemistry (0620)
Complete Revision Modules

Syllabus Alignment Notice: These notes track the entire Cambridge IGCSE Chemistry 0620 core and extended framework. All molecular configurations, state laws, reaction constants, structural frameworks, and essential qualitative analytical tests are fully populated below.

1. States of Matter

The kinetic particle theory defines the physical configurations of matter based on particle distance, arrangement, and velocity profile.

1.1 Arrangement and Movement

  • Solids: Fixed structure, closely packed in a regular lattice. Particles vibrate about fixed positions. Minimal kinetic profile.
  • Liquids: Close together but arranged randomly. Particles slide past one another, taking the shape of their container base.
  • Gases: Far apart, moving rapidly and randomly in straight paths. High collision frequencies and maximal spacing.

1.2 Heating and Cooling Curves

During transitions (melting/boiling), energy added breaks interpersonal bonds without raising temperature. Conversely, during freezing/condensing, structural bonds release thermal capacity, keeping temperature plates steady.

\[ \text{Melting: Solid} \rightarrow \text{Liquid} \quad | \quad \text{Boiling: Liquid} \rightarrow \text{Gas} \] \[ \text{Condensing: Gas} \rightarrow \text{Liquid} \quad | \quad \text{Freezing: Liquid} \rightarrow \text{Solid} \]

1.3 Diffusion and Gas Mass Relationships

Diffusion: The net movement of particles from a region of higher concentration to a region of lower concentration, driven by random kinetic motion. The rate of diffusion depends directly on the relative molecular mass (\(M_r\)) of the gas: lighter molecules move and diffuse faster.

2. Experimental Techniques and Chemical Analysis

Precision tools are used to separate, purify, identify, and measure chemical components.

2.1 Separation and Purification

  • Filtration: Separates an insoluble solid solute from a liquid solvent phase.
  • Crystallization: Recovers a crystalline solid solute from a hot saturated solution.
  • Simple Distillation: Separates a volatile liquid from a non-volatile dissolved solid solute.
  • Fractional Distillation: Separates miscible liquids based on differences in their boiling points using a fractionating column.
  • Paper Chromatography: Separates mixtures of soluble substances (e.g., inks, dyes) based on differential partitioning between a mobile phase and a stationary phase.
Retention Factor: \[ R_f = \frac{\text{Distance travelled by substance}}{\text{Distance travelled by solvent front}} \]

2.2 Qualitative Analysis: Ion Identification Tests

Cation Ion Effect of Aqueous Sodium Hydroxide (\(\text{NaOH}\)) Effect of Aqueous Ammonia (\(\text{NH}_3\))
Aluminum (\(\text{Al}^{3+}\)) White precipitate, dissolves in excess to give a colorless solution White precipitate, insoluble in excess
Ammonium (\(\text{NH}_4^+\)) Ammonia gas produced on warming (turns damp red litmus paper blue) N/A
Calcium (\(\text{Ca}^{2+}\)) White precipitate, insoluble in excess No precipitate or very slight white precipitate
Copper(II) (\(\text{Cu}^{2+}\)) Light blue precipitate, insoluble in excess Light blue precipitate, dissolves in excess to give a dark blue solution
Iron(II) (\(\text{Fe}^{2+}\)) Green precipitate, insoluble in excess Green precipitate, insoluble in excess
Iron(III) (\(\text{Fe}^{3+}\)) Red-brown precipitate, insoluble in excess Red-brown precipitate, insoluble in excess
Zinc (\(\text{Zn}^{2+}\)) White precipitate, dissolves in excess to give a colorless solution White precipitate, dissolves in excess to give a colorless solution

2.3 Anion Verification Protocols

Anion Test Reagent Used Observation Result
Carbonate (\(\text{CO}_3^{2-}\)) Add dilute acid (\(\text{HCl}\)) Effervescence; Carbon Dioxide produced turns limewater milky
Chloride (\(\text{Cl}^-\)) Acidify with dilute \(\text{HNO}_3\), add aqueous \(\text{AgNO}_3\) White precipitate forms
Bromide (\(\text{Br}^-\)) Acidify with dilute \(\text{HNO}_3\), add aqueous \(\text{AgNO}_3\) Cream precipitate forms
Iodide (\(\text{I}^-\)) Acidify with dilute \(\text{HNO}_3\), add aqueous \(\text{AgNO}_3\) Yellow precipitate forms
Nitrate (\(\text{NO}_3^-\)) Add aqueous \(\text{NaOH}\), then aluminum foil; warm gently Ammonia gas produced (turns damp red litmus blue)
Sulfate (\(\text{SO}_4^{2-}\)) Acidify with dilute \(\text{HNO}_3\), add aqueous \(\text{Ba(NO}_3)_2\) White precipitate forms

3. Atoms, Elements and Compounds

The underlying electronic configurations that govern chemical bonding and periodic trends.

3.1 Atomic Framework and Isotopes

An atom consists of a dense nucleus containing protons and neutrons, surrounded by electrons in shells. Standard notation is given by \({}_{Z}^{A}\text{X}\), where \(A\) is the mass number and \(Z\) is the atomic number.

Isotopes: Atoms of the same element with the same number of protons but different numbers of neutrons. They exhibit identical chemical properties because they share the same electronic configuration.

3.2 Bonding Mechanisms

  • Ionic Bonding: Electrostatic attraction between oppositely charged ions, formed by the transfer of electrons from a metal to a non-metal. Features high melting points and conducts electricity when molten or aqueous.
  • Covalent Bonding: Electrostatic attraction between a shared pair of electrons and the positive nuclei of the non-metal atoms involved.
    • Simple Molecular: Low melting points due to weak intermolecular forces (e.g., \(\text{H}_2\text{O}\), \(\text{CO}_2\)).
    • Giant Covalent Structures: High melting points due to strong covalent networks. Examples include Diamond (tetrahedral arrangement, hard, non-conductive) and Graphite (hexagonal layers, soft, sliding planes, contains delocalized electrons that conduct electricity).
  • Metallic Bonding: Electrostatic attraction between a lattice of positive metal ions and a surrounding sea of delocalized valence electrons. Explains malleability and excellent thermal/electrical conductivity.

4. Stoichiometry

Quantitative chemistry balances mass calculations with gas laws and solution concentrations.

Moles (Mass): \[ n = \frac{\text{Mass (g)}}{M_r} \] Moles (Gas Volume): \[ n = \frac{\text{Volume (dm}^3\text{)}}{24.0} \quad (\text{at room temperature and pressure}) \] Moles (Solutions): \[ n = C \times V \quad (\text{where } V \text{ is in dm}^3) \] Concentration Conversion: \[ \text{g/dm}^3 = \text{mol/dm}^3 \times M_r \]

4.2 Empirical Formula Calculations

To find the empirical formula, divide the mass or percentage of each element by its relative atomic mass (\(A_r\)) to get the molar ratio, then divide by the smallest value to obtain the simplest whole-number ratio.

4.3 Yield and Atom Economy Calculations

\[ \text{Percentage Yield} = \frac{\text{Actual Mass Produced}}{\text{Theoretical Calculated Mass}} \times 100\% \] \[ \text{Percentage Purity} = \frac{\text{Mass of Pure Substance}}{\text{Total Mass of Impure Sample}} \times 100\% \]

5. Electricity and Chemistry (Electrolysis)

Electrolysis uses direct current electricity to decompose electrolytes into their component elements.

During electrolysis, oxidation occurs at the positive anode, while reduction takes place at the negative cathode. The products formed depend on the position of the ions in the reactivity series.

5.1 Core Electrolysis Examples

  • Molten Lead(II) Bromide (\(\text{PbBr}_2\)): Cathode produces shiny Lead metal droplets. Anode releases pungent brown Bromine gas.
  • Concentrated Aqueous Sodium Chloride (\(\text{Brine}\)): Cathode yields Hydrogen gas (preferred over Sodium because \(\text{H}^+\) is lower in the reactivity series). Anode yields Chlorine gas. Sodium and Hydroxide ions remain behind, turning the solution alkaline (\(\text{NaOH}\)).
Cathode Half-Equation example: \[ \text{Cu}^{2+} + 2e^- \rightarrow \text{Cu} \quad (\text{Reduction}) \] Anode Half-Equation example: \[ 2\text{Cl}^- \rightarrow \text{Cl}_2 + 2e^- \quad (\text{Oxidation}) \]

5.2 Refining and Hydrogen Fuel Cells

Copper Refining: Uses an impure Copper anode, a pure Copper cathode, and aqueous Copper(II) sulfate electrolyte. Copper transfers from anode to cathode, leaving impurities behind as anode sludge.

Hydrogen Fuel Cells: Clean power generation method. Hydrogen gas reacts at the anode, while oxygen reacts at the cathode to produce water as the only byproduct.

6. Chemical Energetics

Thermodynamics tracks enthalpy changes and net energy movement during chemical transformations.

  • Exothermic Reactions: Release thermal energy to the surroundings (\(\Delta H\) is negative). Energy released making bonds is greater than the energy required to break bonds.
  • Endothermic Reactions: Absorb thermal energy from the surroundings (\(\Delta H\) is positive). Energy required to break bonds is greater than the energy released during bond making.
Enthalpy Calculation: \[ \Delta H = \sum(\text{Energy absorbed in bond breaking}) - \sum(\text{Energy released in bond making}) \]

7. Chemical Reactions

Tracks kinetic collision configurations and the dynamic balancing of reversible systems.

7.1 Factors Affecting Reaction Rates

According to collision theory, a reaction occurs when reacting particles collide with sufficient energy (greater than or equal to the activation energy) and in the correct orientation. The rate of reaction can be increased by:

  • Concentration/Pressure: Increases the number of particles per unit volume, which increases collision frequency.
  • Temperature: Gives particles more kinetic energy, which increases collision frequency and ensures a larger fraction of collisions have energy \(\ge E_a\).
  • Surface Area: Exposes more reacting sites for solid particles to collide with other reactants.
  • Catalysts: Provide an alternative pathway with lower activation energy, increasing successful collision frequency without being consumed by the reaction.

7.2 Reversible Reactions and Industrial Equilibria

A system reaches dynamic equilibrium when the forward and reverse reactions proceed at identical rates in a closed system, keeping the concentrations of reactants and products constant.

Industrial Synthesis Balanced Equation Optimized Reaction Conditions
Haber Process (Ammonia) \[ \text{N}_2\text{(g)} + 3\text{H}_2\text{(g)} \rightleftharpoons 2\text{NH}_3\text{(g)} \] \(450^\circ\text{C}\), \(200 \, \text{atm}\), Finely divided Iron catalyst
Contact Process (Sulfuric Acid) \[ 2\text{SO}_2\text{(g)} + \text{O}_2\text{(g)} \rightleftharpoons 2\text{SO}_3\text{(g)} \] \(450^\circ\text{C}\), \(1-2 \, \text{atm}\), Vanadium(V) Oxide (\(\text{V}_2\text{O}_5\)) catalyst

8. Acids, Bases and Salts

The chemistry of proton transfer and standard methods for synthesizing salts.

8.1 Acid-Base Indicators and pH

  • Acids: Proton (\(\text{H}^+\)) donors. Strong acids completely dissociate in aqueous solution, whereas weak acids only partially dissociate.
  • Bases: Proton (\(\text{H}^+\)) acceptors. Soluble bases are called alkalis and release hydroxide (\(\text{OH}^-\)) ions in water.
\[ \text{Neutralization Equation: H}^+\text{(aq)} + \text{OH}^-\text{(aq)} \rightarrow \text{H}_2\text{O(l)} \]

8.2 Salt Preparation Matrix

  • Soluble Salts (Method A): Add excess insoluble metal, oxide, or carbonate to an acid, filter out the excess unreacted solid, heat the filtrate to its crystallization point, and let it cool.
  • Soluble Salts (Method B - Titration): Used for Sodium, Potassium, and Ammonium salts. Mix exact volumes of acid and alkali using a burette, volumetric pipette, and indicator, then repeat without the indicator before crystallizing.
  • Insoluble Salts (Precipitation): Mix two soluble salt solutions, filter out the precipitate, wash the residue with distilled water to remove impurities, and dry the pure salt in an oven.

9. The Periodic Table

The arrangement of elements based on increasing proton number reveals clear repeating patterns and trends.

9.1 Group Trends

  • Group 1 (Alkali Metals): Soft metals whose melting points decrease down the group, while their reactivity increases because the outermost electron is farther from the nucleus and easier to lose.
  • Group 7 (Halogens): Diatomic non-metals whose colors darken down the group (Chlorine is a pale green gas, Bromine is a red-brown liquid, Iodine is a grey-black solid). Reactivity decreases down the group. More reactive halogens will displace less reactive halide ions from their solutions.
  • Group 8/0 (Noble Gases): Unreactive non-metals with a stable, full outer shell of valence electrons.

9.2 Transition Elements

Transition elements are hard, dense metals characterized by variable oxidation states (e.g., \(\text{Fe}^{2+}\) vs \(\text{Fe}^{3+}\)), the formation of colored compounds, and excellent catalytic properties.

10. Metals

Examines extraction techniques, alloy structures, and reactivity patterns.

10.1 The Reactivity Series

Metals are arranged in order of their readiness to form positive ions:


\(\text{K > Na > Ca > Mg > Al > C > Zn > Fe > H > Cu > Ag > Au}\).

Alloys are mixtures of a metal with other elements; they are harder than pure metals because the different atom sizes disrupt the regular layer structure, preventing them from sliding past one another easily.

10.2 Extraction of Iron (Blast Furnace)

The raw materials loaded into the top of the blast furnace are iron ore (hematite), coke, limestone, and hot air at the base.

Production of Carbon Monoxide: \[ \text{C} + \text{O}_2 \rightarrow \text{CO}_2 \quad | \quad \text{CO}_2 + \text{C} \rightarrow 2\text{CO} \] Reduction of Iron(III) Oxide: \[ \text{Fe}_2\text{O}_3 + 3\text{CO} \rightarrow 2\text{Fe} + 3\text{CO}_2 \] Slag Formation (Removal of Silicon Dioxide impurity): \[ \text{CaCO}_3 \rightarrow \text{CaO} + \text{CO}_2 \quad | \quad \text{CaO} + \text{SiO}_2 \rightarrow \text{CaSiO}_3 \]

10.3 Extraction of Aluminum

Aluminum is extracted from its purified ore, bauxite, via electrolysis. The aluminum oxide (\(\text{Al}_2\text{O}_3\)) is dissolved in molten cryolite to lower its melting point from over \(2000^\circ\text{C}\) to around \(950^\circ\text{C}\), which saves a massive amount of energy. The carbon anodes must be replaced regularly because they react with the evolved oxygen gas to form carbon dioxide.

11. Chemistry of the Environment

Chemical tracking of atmospheric balance, water purity, and greenhouse impacts.

Clean, dry air consists of approximately **78% Nitrogen (\(\text{N}_2\))**, **21% Oxygen (\(\text{O}_2\))**, with the remainder composed of noble gases and carbon dioxide.

11.1 Air Pollutants and Environmental Impact

  • Carbon Monoxide (\(\text{CO}\)): Formed from the incomplete combustion of carbon-containing fuels. It binds irreversibly to hemoglobin, blocking oxygen transport in blood.
  • Sulfur Dioxide (\(\text{SO}_2\)) & Oxides of Nitrogen (\(\text{NO}_x\)): Formed from burning sulfur impurities in fossil fuels and high-temperature car engines. These gases cause acid rain, which damages buildings, acidifies lakes, and harms aquatic life.

11.2 Water Purification Steps

The standard process for treating water involves: filtration through sand beds to remove insoluble particles, sedimentation to allow larger solids to settle, and chlorination to kill harmful microbes and bacteria.

12. Organic Chemistry

The study of carbon-based compounds, functional groups, and polymerization mechanisms.

12.1 Functional Group Summary Table

Homologous Series Functional Group General Formula Key Reaction Conditions
Alkanes \(\text{C-C}\) Single bond \[ \text{C}_n\text{H}_{2n+2} \] Substitution with halogens under Ultraviolet (UV) light
Alkenes \(\text{C=C}\) Double bond \[ \text{C}_n\text{H}_{2n} \] Addition of steam (\(300^\circ\text{C}\), \(60 \, \text{atm}\), \(\text{H}_3\text{PO}_4\) catalyst)
Alcohols \(\text{-OH}\) Hydroxyl group \[ \text{C}_n\text{H}_{2n+1}\text{OH} \] Fermentation of glucose (Warm temperature, Yeast, anaerobic conditions)
Carboxylic Acids \(\text{-COOH}\) Carboxyl group \[ \text{C}_n\text{H}_{2n+1}\text{COOH} \] Oxidation of alcohols using acidified Potassium Manganate(VII)

12.2 Saturated vs Unsaturated Hydrocarbons

Alkanes are saturated molecules because they only contain single bonds, while alkenes are unsaturated because they contain a reactive \(\text{C=C}\) double bond. To test for unsaturation, shake the sample with Bromine Water. An alkene will quickly turn the orange-brown solution **colorless**, while an alkane will remain orange-brown unless exposed to UV light.

12.3 Esterification

Esters are produced when a carboxylic acid reacts with an alcohol in the presence of an acid catalyst (such as concentrated \(\text{H}_2\text{SO}_4\)), yielding a sweet-smelling compound and a water molecule.

\[ \text{Ethanoic Acid} + \text{Ethanol} \xrightarrow{\text{H}_2\text{SO}_4} \text{Ethyl Ethanoate} + \text{Water} \] Structural Linkage: \[ \text{-C(=O)-O-} \]

12.4 Polymers

  • Addition Polymerization: Double bonds in unsaturated monomers open up and join together to form a long polymer chain as the only product (e.g., poly(ethene)).
  • Condensation Polymerization: Bifunctional monomers react together to form a polymer chain, losing a small molecule (such as water) with each link formed (e.g., nylon, terylene).