Chemistry IGCSE Revision 2025
Acid Rain - ansCaused when water and oxygen in the atmosphere react with sulphur dioxide to produce sulphuric acid or
with various oxides of nitrogen to give nitric acid. SO2 and NO2 come mainly from power stations and factories burning
fossil fuels or from motor vehicles. Effects: kills trees, causes life in ponds and rivers to die, affects limestones e.g. statues.
Solution: Catalytic converters in cars to convert oxides of nitrogen into nitrogen gas but have no effect on SO2. Also,
"scrubbers" in chimneys.
Acids and Alkalis - ansAll acids contain H, all alkalis contain OH.
Alkanes and Alkenes - ansAlkanes: CnH2n+2
Alkenes: CnH2n
Alkenes have a carbon-carbon double bond so are unsaturated because they don't have as many hydrogens as possible. To
test for unsaturation, shake with bromine water. If unsaturated, bromine will turn from red/brown to colourless because
an addition reaction will have taken place. The double bond will have broken and joined to a bromine atom.
Alloys - ansAn alloy is a mixture of metals, e.g. brass is a mixture of copper and zinc. In an alloy, the different metals have
slightly differently sized atoms. This breaks up the regular arrangement and makes it more difficult for the layers to slide.
Anion - ansNegative Ion
Blast Furnace - ansIngredients: Coke, Iron Ore (haematite), Limestone
CaCO3 --> CaO + CO2
CO2 + C --> 2CO
C + O2 --> CO2
Fe2O3 + 3CO --> 2Fe + 3CO2
CaO + SiO2 --> CaSiO3 (slag)
Slag floats on top of molten iron so can be tapped off. Used for road building.
Carbon Dioxide - ansMaking: Dilute HCl and CaCO3 in form of marble chips. Or heat a metal carbonate and it turns to
carbon dioxide and metal oxide.
Test: turns lime water milky.
, Uses: Fizzy drinks because it dissolves in water under pressure. Fire extinguishers because the gas is denser than air so
sinks onto the flames and prevents any more oxygen from reaching them.
Cation - ansPositive Ion
Changes of State - ansSolid --> Liquid - Melting
Liquid --> Solid - Freezing
Liquid --> Gas - Boiling
Gas --> Liquid - Condensing
Solid --> Gas and Gas --> Solid - Sublimation
Collecting Gases - ansThree ways: downwards delivery, upward delivery or over water. Also, in a gas syringe if you want to
measure the volume.
Remember hydrogen extinguishes a lighted splint with a "pop."
Combustion - ansComplete combustion is burning an alkane/alkene with excess oxygen and produces carbon dioxide and
water. Incomplete combustion is burning an alkane/alkene with a limited amount of oxygen and this produces carbon
monoxide instead of carbon dioxide.
Covalent Bonding - ansBetween 2 non-metals
1) insoluble in water
2) brittle solids, liquids or gases at room temperature
3) don't conduct electricity when molten
4) lower melting and boiling points - molecules are held together by weak intermolecular forces that are easy to break
Diatomic Gases: a nitrogen molecule has a triple bond, a carbon dioxide molecule has two double bonds, an oxygen
molecule has two double bonds.
Definitions for Organic Chemistry - ansIsomer - same molecular formula but different structural formula
Homologous Series - family of compounds with similar properties because they have similar bonding.
Acid Rain - ansCaused when water and oxygen in the atmosphere react with sulphur dioxide to produce sulphuric acid or
with various oxides of nitrogen to give nitric acid. SO2 and NO2 come mainly from power stations and factories burning
fossil fuels or from motor vehicles. Effects: kills trees, causes life in ponds and rivers to die, affects limestones e.g. statues.
Solution: Catalytic converters in cars to convert oxides of nitrogen into nitrogen gas but have no effect on SO2. Also,
"scrubbers" in chimneys.
Acids and Alkalis - ansAll acids contain H, all alkalis contain OH.
Alkanes and Alkenes - ansAlkanes: CnH2n+2
Alkenes: CnH2n
Alkenes have a carbon-carbon double bond so are unsaturated because they don't have as many hydrogens as possible. To
test for unsaturation, shake with bromine water. If unsaturated, bromine will turn from red/brown to colourless because
an addition reaction will have taken place. The double bond will have broken and joined to a bromine atom.
Alloys - ansAn alloy is a mixture of metals, e.g. brass is a mixture of copper and zinc. In an alloy, the different metals have
slightly differently sized atoms. This breaks up the regular arrangement and makes it more difficult for the layers to slide.
Anion - ansNegative Ion
Blast Furnace - ansIngredients: Coke, Iron Ore (haematite), Limestone
CaCO3 --> CaO + CO2
CO2 + C --> 2CO
C + O2 --> CO2
Fe2O3 + 3CO --> 2Fe + 3CO2
CaO + SiO2 --> CaSiO3 (slag)
Slag floats on top of molten iron so can be tapped off. Used for road building.
Carbon Dioxide - ansMaking: Dilute HCl and CaCO3 in form of marble chips. Or heat a metal carbonate and it turns to
carbon dioxide and metal oxide.
Test: turns lime water milky.
, Uses: Fizzy drinks because it dissolves in water under pressure. Fire extinguishers because the gas is denser than air so
sinks onto the flames and prevents any more oxygen from reaching them.
Cation - ansPositive Ion
Changes of State - ansSolid --> Liquid - Melting
Liquid --> Solid - Freezing
Liquid --> Gas - Boiling
Gas --> Liquid - Condensing
Solid --> Gas and Gas --> Solid - Sublimation
Collecting Gases - ansThree ways: downwards delivery, upward delivery or over water. Also, in a gas syringe if you want to
measure the volume.
Remember hydrogen extinguishes a lighted splint with a "pop."
Combustion - ansComplete combustion is burning an alkane/alkene with excess oxygen and produces carbon dioxide and
water. Incomplete combustion is burning an alkane/alkene with a limited amount of oxygen and this produces carbon
monoxide instead of carbon dioxide.
Covalent Bonding - ansBetween 2 non-metals
1) insoluble in water
2) brittle solids, liquids or gases at room temperature
3) don't conduct electricity when molten
4) lower melting and boiling points - molecules are held together by weak intermolecular forces that are easy to break
Diatomic Gases: a nitrogen molecule has a triple bond, a carbon dioxide molecule has two double bonds, an oxygen
molecule has two double bonds.
Definitions for Organic Chemistry - ansIsomer - same molecular formula but different structural formula
Homologous Series - family of compounds with similar properties because they have similar bonding.
