G3 Science Chemistry Revision Guide

• Revision Guide
• Secondary Science
• Syllabus K326 / K328
• Reviewed by MiniEducation Team

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K326 / K328 G3 Science Chemistry revision guide covering definitions, formulae, observations, tests, conditions and exam traps without Pure-only depth.

1. Important Definitions

2. Key Chemistry Maths

For every stoichiometry question:

1. balance the equation;
2. convert the known quantity to moles;
3. apply the coefficient ratio;
4. convert the required moles to the requested quantity;
5. include units and sensible precision.

3. Experimental Chemistry, Particles and Bonding

• Solid particles vibrate about fixed positions; liquid particles move past one another; gas particles move rapidly and randomly far apart.
• Melting, boiling and sublimation absorb energy. Freezing and condensation release energy.
• Ionic compounds have high melting points and conduct only when molten or aqueous, because their ions are then mobile.
• Simple covalent substances have low melting and boiling points because the attractions between molecules are weak.
• Metals conduct; alloys are harder because different-sized atoms make layer sliding more difficult.

4. Acids, Bases and Neutralisation

The net ionic equation for neutralisation is:

• Basic oxides react with acids; acidic oxides react with bases.
• Amphoteric oxides react with both acids and bases.
• Bases neutralise acidic soil; alkalis also react with ammonium salts to release ammonia.
• Strong/weak acid theory, salt-preparation methods, solubility rules and the Haber process are Pure Chemistry extensions.

5. Qualitative Analysis

Gas tests

Anion tests

Cation precipitates

6. Redox Chemistry

• Oxidation and reduction always occur together.
• Electron loss is oxidation; electron gain is reduction.
• An oxidising agent accepts electrons and is reduced.
• A reducing agent donates electrons and is oxidised.
• Oxidation state increases during oxidation and decreases during reduction.
• Balance atoms and total charge in ionic half-equations.

Electrolysis, electroplating, simple cells and hydrogen fuel cells belong to G3 Pure / O-Level, not K326/K328 G3 Science Chemistry.

7. Periodic Table and Reactivity

• Elements are arranged by increasing proton number.
• Elements in the same group have the same number of outer-shell electrons and similar chemical properties.
• Group 1 reactivity increases down the group.
• Group 17 reactivity decreases down the group; a more reactive halogen displaces a less reactive halide.
• Group 18 elements are unreactive because their atoms have full outer shells.
• Reactivity series: K, Na, Ca, Mg, Al, Zn, Fe, Pb, H, Cu, Ag.
• Metals above carbon are extracted by electrolysis; metals below carbon may be extracted by reduction with carbon.
• Rusting needs oxygen and water. Barrier protection, galvanising and sacrificial protection prevent rust in different ways.

8. Energy Changes and Rates

Energy changes

• Exothermic: energy is transferred to the surroundings, so the surroundings warm.
• Endothermic: energy is taken in from the surroundings, so the surroundings cool.
• State the observed temperature change and the direction of energy transfer.
• Enthalpy signs, energy-profile diagrams, bond-breaking/bond-making energy and activation energy are Pure Chemistry extensions.

Rate of reaction

• Increasing concentration or gas pressure gives more frequent collisions.
• Smaller particles have greater total surface area, so collision frequency increases.
• Higher temperature makes particles move faster, causing more frequent collisions and a greater fraction of sufficiently energetic collisions.
• On a product–time graph, a steeper gradient means a faster rate; a plateau means the measured product is no longer increasing.
• Catalyst definitions and alternative activation-energy pathways are Pure Chemistry extensions.

9. Organic Chemistry

• Crude oil is separated by fractional distillation.
• Complete combustion forms carbon dioxide and water; incomplete combustion may form carbon monoxide and soot.
• Alkanes undergo substitution with halogens in ultraviolet light.
• Alkenes decolourise bromine water and undergo addition.
• Hydrogenation uses hydrogen and a nickel catalyst.
• Ethanol can be oxidised to ethanoic acid.
• Addition polymerisation opens C = C; no small molecule is lost.
• Esters, C4 compounds, structural isomers and condensation polymers are Pure Chemistry extensions.

10. Maintaining Air Quality

Clean, dry air is approximately 78% nitrogen, 21% oxygen, 0.9% noble gases and 0.04% carbon dioxide by volume.

Carbon dioxide and methane absorb outgoing infrared radiation and contribute to global warming. Photosynthesis removes carbon dioxide; respiration, decomposition and combustion return it. Catalytic converters, flue-gas desulfurisation and ozone depletion are Pure Chemistry extensions.

11. High-Value Exam Traps

1. Give the exact observation, then the inference.
2. Use coefficients to balance equations; never alter a chemical formula.
3. Convert cm³ to dm³ before using n = cV.
4. Explain rate changes with collision frequency and, for temperature, the fraction of sufficiently energetic collisions.
5. Do not import Pure-only salt preparation, electrolysis, activation-energy, ester or pollution-control content into a G3 Science answer.