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CAIE 0620 · IGCSE CHEMISTRY · EXTENDED
IGCSE Chemistry 0620 Cheat Sheets — Free Revision & Formula Sheets
The whole Cambridge IGCSE Chemistry (0620) Extended syllabus condensed into 12 topic cheat sheets: every definition, formula, reaction condition and colour change examiners award marks for. Read any sheet online below, or download the complete 12-page revision sheet as a free PDF — no signup required.
- 12 topic cheat sheets
- CAIE 0620 syllabus-mapped
- Extended · Papers 2 & 4
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01 Particles, Definitions & Separation
Cambridge IGCSE Chemistry 0620 — Extended · Papers 2 & 4
| Term | Definition to memorise |
|---|---|
| Element | Substance made of one type of atom, cannot be broken down chemically. |
| Compound | Two or more elements chemically combined in fixed proportions. |
| Mixture | Two or more substances not chemically combined; components keep their properties. |
| Isotopes | Atoms of the same element with the same proton number but different numbers of neutrons. Identical chemical properties (same electron arrangement). |
| Relative atomic mass (Ar) | Average mass of naturally occurring atoms of an element on a scale where 12C = 12. |
| Mole | Amount of substance containing 6.02 × 1023 particles (Avogadro constant). |
| Diffusion | Net movement of particles from high to low concentration. Rate ∝ 1/√Mr — lighter gases diffuse faster (NH3 beats HCl). |
| Solvent / solute / solution | Liquid that dissolves / substance dissolved / the mixture formed. Saturated = no more solute dissolves at that temperature. |
| Allotropes | Different structural forms of the same element (diamond, graphite). |
| Pure substance | Melts/boils at one sharp, fixed temperature. Impurities lower melting point and raise boiling point over a range. |
Separation techniques
| Filtration | Insoluble solid from a liquid. Residue = solid, filtrate = liquid. |
| Crystallisation | Soluble solid from solution — heat to saturation, cool slowly, filter, dry between filter papers. |
| Simple distillation | Solvent from a solution (pure water from seawater). |
| Fractional distillation | Miscible liquids of different boiling points (ethanol 78 °C from water 100 °C; crude oil; liquid air). |
| Paper chromatography | Soluble coloured/colourless substances. Rf = distance moved by substance ÷ distance moved by solvent front. Colourless spots need a locating agent. Pencil baseline, above solvent level. |
02 Atoms, Bonding & Structure
Cambridge IGCSE Chemistry 0620 — Extended · Papers 2 & 4
| Particle | Relative mass | Relative charge | Location |
|---|---|---|---|
| Proton | 1 | +1 | Nucleus |
| Neutron | 1 | 0 | Nucleus |
| Electron | 1/1840 | −1 | Shells / energy levels |
Proton number = protons = electrons (neutral atom). Nucleon number = protons + neutrons. Neutrons = nucleon − proton number. Shell filling 2, 8, 8, 18. Group number = outer electrons; period number = number of shells.
Three types of bond
| Ionic | Metal + non-metal. Electrons transferred; strong electrostatic attraction between oppositely charged ions in a giant lattice. |
| Covalent | Non-metal + non-metal. Shared pairs of electrons; attraction between shared pair and the two nuclei. |
| Metallic | Lattice of positive metal ions in a sea of delocalised electrons; attraction between the two. |
Structure → properties
| Structure | Melting point | Conductivity | Examples & notes |
|---|---|---|---|
| Giant ionic | High — strong forces throughout lattice | Only when molten or aqueous (ions free to move) | NaCl, MgO. Brittle; usually soluble in water. |
| Simple molecular | Low — weak intermolecular forces broken, not covalent bonds | None | H2O, CO2, I2, CH4. Larger molecule → stronger forces → higher b.p. |
| Giant covalent | Very high | Graphite yes, diamond/SiO2 no | Diamond: 4 bonds per C, tetrahedral, hardest — cutting tools. Graphite: 3 bonds per C, hexagonal layers, weak forces between layers slide → lubricant/pencil; 1 delocalised electron per atom → conducts, used as electrodes. SiO2: sand, glass, furnace linings. |
| Metallic | High | Good, solid or liquid (delocalised electrons) | Malleable — layers of ions slide. Alloys are harder: different-sized atoms disrupt the layers. |
Ion charges: Group I +1 · II +2 · III +3 · V −3 · VI −2 · VII −1 · Group 0 none. Common ions: NH4+, Ag+, Zn2+, Pb2+, Cu2+, Fe2+/Fe3+, OH−, NO3−, HCO3−, CO32−, SO42−, PO43−. State symbols: (s) (l) (g) (aq).
03 Stoichiometry — Every Formula
Cambridge IGCSE Chemistry 0620 — Extended · Papers 2 & 4
| moles = mass ÷ Mr | mass in g |
| moles = concentration × volume | conc in mol/dm3, volume in dm3 (cm3 ÷ 1000) |
| moles of gas = volume ÷ 24 | dm3 at r.t.p. (or cm3 ÷ 24 000). Molar gas volume = 24 dm3/mol at r.t.p. |
| conc (g/dm3) = conc (mol/dm3) × Mr | Convert before comparing. |
| % yield = (actual ÷ theoretical) × 100 | Losses: side reactions, reversible reaction, transfer losses. |
| % purity = (mass of pure ÷ mass of impure) × 100 | |
| % composition = (Ar × number of atoms ÷ Mr) × 100 | |
| number of particles = moles × 6.02 × 1023 |
Empirical formula: mass (or %) ÷ Ar → divide all by the smallest → whole-number ratio. Molecular formula: (Mr ÷ empirical mass) × empirical formula. Limiting reagent: the reactant giving the fewest moles of product — all yields are based on it; the other is in excess. Gas volumes react in the same ratio as their balancing numbers.
04 Acids, Bases & Salt Preparation
Cambridge IGCSE Chemistry 0620 — Extended · Papers 2 & 4
| Reaction of an acid | General equation & example |
|---|---|
| Acid + metal | → salt + hydrogen · Mg + 2HCl → MgCl2 + H2 |
| Acid + base/alkali | → salt + water · H2SO4 + 2NaOH → Na2SO4 + 2H2O · ionic: H+ + OH− → H2O |
| Acid + carbonate | → salt + water + carbon dioxide · CaCO3 + 2HCl → CaCl2 + H2O + CO2 |
| Acid + ammonia | → ammonium salt · HNO3 + NH3 → NH4NO3 (fertiliser) |
Acid = proton (H+) donor; base = proton acceptor; alkali = soluble base. Strong acid (HCl, HNO3, H2SO4) fully dissociates; weak acid (ethanoic, carbonic) partially dissociates — lower [H+], higher pH, slower reactions, poorer conductor at the same concentration.
Indicators: litmus red↔blue · thymolphthalein colourless in acid, blue in alkali · methyl orange red in acid, yellow in alkali. Universal indicator: pH 1–3 red, 4–6 orange/yellow, 7 green, 8–11 blue, 12–14 purple.
Oxides: acidic = non-metal (CO2, SO2, NO2) · basic = metal (CuO, CaO, MgO) · amphoteric = Al2O3 and ZnO (react with both acids and alkalis) · neutral = CO, N2O, NO.
Choosing the preparation
| Salt type | Method |
|---|---|
| Soluble (from insoluble base, carbonate or metal) | Add the solid in excess to warm acid until no more reacts → filter off excess → evaporate filtrate to the point of crystallisation → cool → filter → dry between filter papers. |
| Soluble (from a soluble base/alkali) | Titration: find the exact volume with indicator, then repeat with the same volumes and no indicator, then crystallise. |
| Insoluble | Precipitation: mix two soluble salt solutions, filter, wash the residue with distilled water, dry. e.g. Pb(NO3)2 + 2KI → PbI2↓ + 2KNO3 |
Solubility rules: all sodium, potassium, ammonium and nitrate salts are soluble · all chlorides soluble except silver and lead · all sulfates soluble except barium, calcium and lead · all carbonates insoluble except sodium, potassium, ammonium · hydroxides insoluble except sodium, potassium, ammonium (calcium slightly).
Water of crystallisation: hydrated CuSO4·5H2O (blue) ⇌ anhydrous CuSO4 (white) + 5H2O — heating drives it off, adding water reverses it.
05 Redox & Electrolysis
Cambridge IGCSE Chemistry 0620 — Extended · Papers 2 & 4
OIL RIG — Oxidation Is Loss of electrons, Reduction Is Gain. Also: oxidation = gain of oxygen / increase in oxidation number. The oxidising agent is reduced; the reducing agent is oxidised.
Tests: an oxidising agent turns colourless aqueous potassium iodide brown (I2 formed). A reducing agent turns acidified aqueous potassium manganate(VII) from purple to colourless.
Electrolysis: breakdown of an ionic compound, molten or in aqueous solution, by the passage of electricity. Cathode = negative, attracts cations, reduction. Anode = positive, attracts anions, oxidation. Electrolyte conducts because ions are free to move.
| Electrolyte | Cathode (−) | Anode (+) | Notes |
|---|---|---|---|
| Molten PbBr2 (must be molten) | Pb2+ + 2e− → Pb (silvery liquid) | 2Br− → Br2 + 2e− (red-brown vapour) | Inert carbon electrodes. |
| Concentrated NaCl(aq) (brine) | 2H+ + 2e− → H2 | 2Cl− → Cl2 + 2e− | NaOH left in solution. Products: hydrogen, chlorine, sodium hydroxide. |
| Dilute NaCl(aq) | 2H+ + 2e− → H2 | 4OH− → O2 + 2H2O + 4e− | Dilute halide → oxygen instead of the halogen. |
| Dilute H2SO4 / water | H2 | O2 | Volume ratio H2 : O2 = 2 : 1. |
| CuSO4(aq), inert carbon electrodes | Cu2+ + 2e− → Cu (pink-brown coating) | 4OH− → O2 + 2H2O + 4e− | Blue colour fades as Cu2+ is used up. |
| CuSO4(aq), copper electrodes | Cu deposited — cathode gains mass | Cu → Cu2+ + 2e− — anode dissolves, loses mass | Basis of copper purification and electroplating (object = cathode, plating metal = anode, electrolyte = a salt of that metal). |
| Molten Al2O3 in molten cryolite | Al3+ + 3e− → Al | 2O2− → O2 + 4e− | Cryolite lowers the melting point → less energy. Carbon anodes burn away: C + O2 → CO2, so they are replaced regularly. |
Predicting products (aqueous): at the cathode, the less reactive of the metal and hydrogen is discharged — metals below H in the reactivity series are deposited, otherwise hydrogen. At the anode, a halide is discharged if concentrated; otherwise oxygen from OH−.
Hydrogen–oxygen fuel cell: 2H2 + O2 → 2H2O. Only product is water; higher efficiency than combustion, but hydrogen is hard to store and manufacture.
06 Energetics, Rates & Equilibrium
Cambridge IGCSE Chemistry 0620 — Extended · Papers 2 & 4
| Exothermic | Gives out heat, temperature rises, ΔH negative. Products lower in energy. Combustion, neutralisation, respiration, most displacement. |
| Endothermic | Takes in heat, temperature falls, ΔH positive. Thermal decomposition, photosynthesis, electrolysis. |
| Bond energies | Breaking bonds is endothermic, making bonds is exothermic. ΔH = Σ(bonds broken) − Σ(bonds formed), in kJ/mol. |
| Activation energy, Ea | Minimum energy colliding particles need to react — the hump on the energy profile. |
Rate of reaction — collision theory
| Increase | Why the rate rises |
|---|---|
| Concentration (or pressure, for gases) | Particles closer together → more frequent collisions per second. |
| Temperature | Particles move faster → more frequent collisions and a greater proportion have energy ≥ Ea. |
| Surface area (smaller pieces) | More particles exposed → more frequent collisions. |
| Catalyst | Provides an alternative pathway of lower activation energy. Not used up; unchanged in mass and chemical composition. Enzymes are biological catalysts. |
| Light (photochemical) | Supplies energy — e.g. photosynthesis, substitution of alkanes, silver halides in photography. |
Measuring rate: gas volume vs time (syringe), mass loss vs time (balance), or time for a cross to disappear. Rate = gradient; steepest at the start, zero when the line levels off.
Reversible reactions & Le Chatelier
Dynamic equilibrium (closed system): forward and reverse rates are equal, so concentrations stay constant.
| Change | Equilibrium shifts |
|---|---|
| Increase temperature | To the endothermic side. |
| Increase pressure | To the side with fewer moles of gas. |
| Increase concentration of a reactant | To the products (right), to remove it. |
| Add a catalyst | No shift — equilibrium is reached faster; yield is unchanged. |
Classic reversible reaction: CuSO4·5H2O ⇌ CuSO4 + 5H2O (blue ⇌ white) and CoCl2·6H2O ⇌ CoCl2 + 6H2O (pink ⇌ blue).
07 Industrial Processes — Conditions
Cambridge IGCSE Chemistry 0620 — Extended · Papers 2 & 4
| Process | Equation | Conditions | Key points |
|---|---|---|---|
| Haber process (ammonia) | N2 + 3H2 ⇌ 2NH3 | 450 °C · 200 atm · iron catalyst | N2 from air, H2 from methane/natural gas. Unreacted gases recycled; ammonia removed by cooling. Compromise temperature: low T gives more yield but too slowly. |
| Contact process (sulfuric acid) | S + O2 → SO2 2SO2 + O2 ⇌ 2SO3 SO3 + H2O → H2SO4 | 450 °C · 2 atm · vanadium(V) oxide, V2O5 | Only the middle step is reversible/catalysed. Uses of H2SO4: fertilisers, detergents, paints, batteries. |
| Blast furnace (iron from haematite) | C + O2 → CO2 CO2 + C → 2CO Fe2O3 + 3CO → 2Fe + 3CO2 CaCO3 → CaO + CO2 CaO + SiO2 → CaSiO3 | Hot air blast; ~1500 °C. Charge: iron ore, coke, limestone | CO is the reducing agent. Limestone removes sandy impurities as molten slag, which floats on the iron and is tapped off. |
| Aluminium extraction | Al3+ + 3e− → Al (cathode) 2O2− → O2 + 4e− (anode) | Electrolysis of molten Al2O3 dissolved in molten cryolite; carbon electrodes | Too reactive for carbon reduction. Expensive — large amounts of electricity. |
| Chlor-alkali | 2NaCl + 2H2O → 2NaOH + H2 + Cl2 | Electrolysis of concentrated aqueous NaCl (brine) | Cl2: bleach, sterilising water, PVC. NaOH: soap, paper. H2: margarine, ammonia. |
| Cracking | C10H22 → C8H18 + C2H4 | 600–700 °C · silica or alumina catalyst | Long-chain, less useful alkanes → shorter alkanes + alkenes (+ sometimes hydrogen). Supplies alkenes for polymers and extra petrol. |
| Ethanol by hydration | C2H4 + H2O → C2H5OH | 300 °C · 60 atm · phosphoric acid catalyst · steam | Continuous, fast, pure product, but uses a finite resource (crude oil). |
| Ethanol by fermentation | C6H12O6 → 2C2H5OH + 2CO2 | 25–35 °C · yeast · absence of oxygen (anaerobic) | Batch process, slow, impure (needs distillation), but renewable. Above ~37 °C the enzymes denature. |
| Lime kiln | CaCO3 → CaO + CO2 CaO + H2O → Ca(OH)2 | Strong heating (thermal decomposition) | Limestone → quicklime → slaked lime. Used to neutralise acidic soils and lakes, and in cement/iron making. |
| Hydrogenation (margarine) | C2H4 + H2 → C2H6 | 150 °C · nickel catalyst | Hardens unsaturated vegetable oils. |
08 Periodic Table, Metals & Corrosion
Cambridge IGCSE Chemistry 0620 — Extended · Papers 2 & 4
| Group | What to remember |
|---|---|
| I — alkali metals | Soft, low density, low melting points. Stored under oil. Down the group: more reactive (outer electron further from nucleus, more shielding, lost more easily); melting point decreases. 2Na + 2H2O → 2NaOH + H2 — floats, fizzes, alkaline solution. |
| VII — halogens | Diatomic. Cl2 pale yellow-green gas · Br2 red-brown liquid · I2 grey-black solid (purple vapour). Down the group: less reactive, darker, higher melting point. Displacement: a more reactive halogen displaces a less reactive halide — Cl2 + 2KBr → 2KCl + Br2 (solution turns orange). |
| 0 — noble gases | Full outer shell → unreactive, monatomic. Uses: helium in balloons, argon in lamps/welding. |
| Transition elements | High density and melting point, variable oxidation states, coloured compounds, useful as catalysts (Fe in Haber, V2O5 in Contact, Ni in hydrogenation). |
| Across a period | Metallic → non-metallic character. Metals lose electrons to form positive ions; non-metals gain electrons to form negative ions. |
Reactivity series & extraction
K · Na · Ca · Mg · Al · (C) · Zn · Fe · (H) · Cu · Ag · Au — most to least reactive. Carbon and hydrogen are included for comparison.
| Metal | Cold water | Steam | Dilute acid | Extraction |
|---|---|---|---|---|
| K, Na, Ca | Vigorous → hydroxide + H2 | Violent | Dangerously violent | Electrolysis of the molten compound (above carbon) |
| Mg, Al | Very slow / none | Reacts → oxide + H2 | Reacts → salt + H2 | |
| Zn, Fe, Pb | None | Slow (reversible for Fe) | Reacts → salt + H2 | Reduction with carbon (below carbon) |
| Cu, Ag, Au | None | None | None | Found native or by simple heating |
Rusting: iron + oxygen + water both required → hydrated iron(III) oxide. Salt speeds it up. Prevention: barrier methods (paint, grease, plastic) · galvanising (zinc coating: barrier and sacrificial) · sacrificial protection — a more reactive metal (Zn, Mg) corrodes instead, losing electrons in place of the iron.
Alloys: brass = copper + zinc · stainless steel = iron + chromium + nickel (resists corrosion) · mild steel = iron + a little carbon. Uses: aluminium — aircraft, food cans, overhead cables (low density, oxide layer resists corrosion); copper — wiring, pipes (ductile, good conductor).
09 Air, Water & the Environment
Cambridge IGCSE Chemistry 0620 — Extended · Papers 2 & 4
Clean dry air: 78% nitrogen, 21% oxygen, ~1% argon (noble gases), ~0.04% carbon dioxide.
| Pollutant | Source | Effect |
|---|---|---|
| Carbon monoxide, CO | Incomplete combustion of carbon fuels | Toxic — binds to haemoglobin, reduces oxygen transport. |
| Sulfur dioxide, SO2 | Combustion of fuels containing sulfur compounds | Acid rain — damages buildings/limestone, kills trees and aquatic life. |
| Oxides of nitrogen, NOx | N2 + O2 react in car engines at high temperature | Acid rain, photochemical smog, respiratory problems. |
| Particulates | Incomplete combustion | Respiratory problems; increased risk of cancer. |
| Methane, CO2 | Livestock, decomposition, respiration, combustion | Greenhouse gases — absorb re-radiated infrared, raising Earth’s temperature (climate change). |
Catalytic converter: 2CO + 2NO → 2CO2 + N2 — reduces CO and NOx emissions. Flue-gas desulfurisation: CaO + SO2 → CaSO3.
Photosynthesis (endothermic): 6CO2 + 6H2O → C6H12O6 + 6O2 · conditions: light and chlorophyll.
Water treatment: sedimentation and filtration remove solids; chlorination kills microbes. Distilled water is used in practical chemistry because tap water contains dissolved ions.
Fertilisers: NPK supply nitrogen (protein/growth), phosphorus and potassium. Ammonium salts and nitrates come from ammonia: NH3 + HNO3 → NH4NO3. Excess fertiliser causes eutrophication.
10 Organic Chemistry
Cambridge IGCSE Chemistry 0620 — Extended · Papers 2 & 4
| Series | General formula | Functional group | First four members |
|---|---|---|---|
| Alkanes | CnH2n+2 | None (saturated, single bonds) | methane CH4 · ethane C2H6 · propane C3H8 · butane C4H10 |
| Alkenes | CnH2n | C=C (unsaturated) | ethene C2H4 · propene C3H6 · butene C4H8 · pentene C5H10 |
| Alcohols | CnH2n+1OH | −OH | methanol · ethanol C2H5OH · propanol · butanol |
| Carboxylic acids | CnH2n+1COOH | −COOH | methanoic · ethanoic CH3COOH · propanoic · butanoic |
| Esters | — | −COO− | ethyl ethanoate CH3COOC2H5 — sweet smell, used in perfumes and flavourings |
Homologous series: same general formula and functional group, differing by CH2, similar chemical properties, gradual change in physical properties. Structural isomers: same molecular formula, different structural formula.
Reactions and their conditions
| Reaction | Equation | Conditions |
|---|---|---|
| Complete combustion | CH4 + 2O2 → CO2 + 2H2O | Plenty of oxygen |
| Incomplete combustion | 2CH4 + 3O2 → 2CO + 4H2O | Limited oxygen — gives CO and soot |
| Alkane + halogen (substitution) | CH4 + Cl2 → CH3Cl + HCl | UV light |
| Alkene + bromine (addition) | C2H4 + Br2 → C2H4Br2 | Room temperature — test for unsaturation: bromine water turns orange → colourless |
| Alkene + hydrogen | C2H4 + H2 → C2H6 | 150 °C · nickel catalyst |
| Alkene + steam (hydration) | C2H4 + H2O → C2H5OH | 300 °C · 60 atm · phosphoric acid |
| Fermentation | C6H12O6 → 2C2H5OH + 2CO2 | 25–35 °C · yeast · no oxygen |
| Oxidation of ethanol | C2H5OH + 2[O] → CH3COOH + H2O | Heat under reflux with acidified potassium manganate(VII) — purple to colourless; or bacterial oxidation in air |
| Esterification | CH3COOH + C2H5OH ⇌ CH3COOC2H5 + H2O | Warm · concentrated sulfuric acid catalyst |
| Acid reactions of ethanoic acid | with metals → salt + H2 · with carbonates → salt + H2O + CO2 · with alkalis → salt + water (ethanoates) | Weak acid — partially dissociated |
| Addition polymerisation | n C2H4 → −(CH2−CH2)n− (poly(ethene)) | Many alkene monomers, C=C opens; one product only |
| Condensation polymerisation | Polyester (PET) from a diol + a dicarboxylic acid; nylon from a diamine + a dicarboxylic acid | Two monomers with two functional groups; a small molecule (H2O or HCl) is lost each link |
Fractional distillation of petroleum (fractions in order, decreasing volatility, increasing boiling point and chain length): refinery gas (bottled fuel) · gasoline/petrol (cars) · naphtha (chemical feedstock) · kerosene/paraffin (jet fuel) · diesel oil (engines) · fuel oil (ships, heating) · bitumen (road surfacing).
Uses of ethanol: solvent and fuel. Plastics: non-biodegradable; disposal in landfill causes pollution, burning PVC releases toxic HCl.
11 Qualitative Analysis — Tests & Colours
Cambridge IGCSE Chemistry 0620 — Extended · Papers 2 & 4
Tests for gases
| Hydrogen, H2 | Lighted splint → squeaky pop |
| Oxygen, O2 | Glowing splint relights |
| Carbon dioxide, CO2 | Limewater turns milky / cloudy white |
| Chlorine, Cl2 | Damp litmus paper is bleached white |
| Ammonia, NH3 | Damp red litmus turns blue; pungent smell |
| Sulfur dioxide, SO2 | Acidified potassium manganate(VII) turns from purple to colourless |
| Water | Anhydrous copper(II) sulfate white → blue; anhydrous cobalt(II) chloride blue → pink. Purity is confirmed by a boiling point of exactly 100 °C / melting point 0 °C. |
Tests for cations
| Ion | Adding aqueous sodium hydroxide | Adding aqueous ammonia |
|---|---|---|
| Al3+ | White ppt, soluble in excess → colourless solution | White ppt, insoluble in excess |
| Ca2+ | White ppt, insoluble in excess | No precipitate (or very slight white) |
| Cr3+ | Green ppt, soluble in excess → green solution | Green ppt, insoluble in excess |
| Cu2+ | Light blue ppt, insoluble in excess | Light blue ppt, soluble in excess → dark blue solution |
| Fe2+ | Green ppt, insoluble in excess (turns brown at the surface) | Green ppt, insoluble in excess |
| Fe3+ | Red-brown ppt, insoluble in excess | Red-brown ppt, insoluble in excess |
| Zn2+ | White ppt, soluble in excess → colourless | White ppt, soluble in excess → colourless |
| NH4+ | Warm with aqueous sodium hydroxide → ammonia gas, turns damp red litmus blue | |
Tests for anions
| Carbonate, CO32− | Add dilute acid → effervescence, gas turns limewater milky. |
| Chloride, Cl− | Acidify with dilute nitric acid, add aqueous silver nitrate → white ppt. |
| Bromide, Br− | Same test → cream ppt. |
| Iodide, I− | Same test → yellow ppt. |
| Nitrate, NO3− | Add aqueous sodium hydroxide and aluminium foil, then warm → ammonia gas (damp red litmus blue). |
| Sulfate, SO42− | Acidify with dilute nitric acid, add aqueous barium nitrate → white ppt. |
| Sulfite, SO32− | Add acidified aqueous potassium manganate(VII) → purple to colourless. |
Flame tests
| Li+ red | Na+ yellow | K+ lilac | Ca2+ orange-red | Ba2+ light green · Cu2+ blue-green |
Method: clean the wire in concentrated hydrochloric acid, dip in the solid, hold in a hot blue Bunsen flame.
12 Mnemonics & Memory Hooks
Cambridge IGCSE Chemistry 0620 — Extended · Papers 2 & 4
| Mnemonic | What it holds |
|---|---|
| OIL RIG | Oxidation Is Loss of electrons · Reduction Is Gain. |
| An Ox / Red Cat | Anode = Oxidation · Reduction = Cathode. |
| PANIC | Positive is Anode, Negative Is Cathode (in electrolysis). |
| “Please Send Cats, Monkeys And Cute Zebras Into Hot Countries Signed General” | Potassium, Sodium, Calcium, Magnesium, Aluminium, Carbon, Zinc, Iron, Hydrogen, Copper, Silver, Gold — the reactivity series in order. |
| “Met Eth Prop But” | meth- 1 C, eth- 2 C, prop- 3 C, but- 4 C, pent- 5 C. |
| Alkane = A-lone | Alkanes are saturated, single bonds only; alkenes have a double bond. |
| Iron in the Haber, Vanadium in the Contact | Both run at 450 °C — only the pressure differs: 200 atm (Haber) vs 2 atm (Contact). |
| Endo takes, Exo exits | Endothermic takes heat in, ΔH positive · exothermic gives heat out, ΔH negative. |
| “White, Cream, Yellow” | Silver nitrate precipitates in halogen order: chloride, bromide, iodide. |
| Zinc and Aluminium are the “excess twins” | Both give a white precipitate that dissolves in excess NaOH — only zinc also dissolves in excess ammonia. |
| “Nitrates Are Never Insoluble” | All nitrates, and all sodium/potassium/ammonium salts, are soluble. |
| MAD CAT | Rate of reaction rises with More concentration, Added catalyst, Divided solid (surface area), and higher Temperature. |
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BOOK A FREE DEMOIGCSE Chemistry Cheat Sheets — Frequently Asked Questions
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