Chemistry IGCSE Revision
Acid Rain - ANS - Caused 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 - ANS - All acids contain H, all alkalis contain OH.
\Alkanes and Alkenes - ANS - Alkanes: 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 - ANS - An 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 - ANS - Negative Ion
\Blast Furnace - ANS - Ingredients: 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 - ANS - Making: 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 - ANS - Positive Ion
\Changes of State - ANS - Solid --> Liquid - Melting
Liquid --> Solid - Freezing
, Liquid --> Gas - Boiling
Gas --> Liquid - Condensing
Solid --> Gas and Gas --> Solid - Sublimation
\Collecting Gases - ANS - Three 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 - ANS - Complete 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 - ANS - Between 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 - ANS - Isomer - same molecular formula but
different structural formula
Homologous Series - family of compounds with similar properties because they
have similar bonding.
\Diffusion - ANS - The spreading out of particles in a gas or a liquid. The lighter
the particles, the faster they diffuse. This is demonstrated by the experiment with
cotton wool soaked in ammonia solution at one end of a tube and cotton wool
soaked in HCl at the other end. The white cloud of ammonium chloride forms
closer to the hydrochloric end. Also to speed up diffusion, you can stir a liquid or
heat up the liquid or gas.
\Flame Test - ANS - Red shows lithium ions
Orange shows sodium ions
Lilac shows potassium ions
Brick Red shows calcium ions
\Gas - ANS - Particles are much further apart and there are almost no forces of
attraction between them.
\Giant Covalent Structures - ANS - Diamond - 4 strong bonds so very high melting
and boiling points. Cannot conduct electricity because no free ions to move and
carry charge. Insoluble. Silican dioxide has similar properties to diamond.
Carbon - 3 strong bonds but 4 ions so there's a free one to move and carry
charge so carbon can conduct electricity. Good lubricant as carbon is made up in
sheets which can slide over each other.
Acid Rain - ANS - Caused 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 - ANS - All acids contain H, all alkalis contain OH.
\Alkanes and Alkenes - ANS - Alkanes: 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 - ANS - An 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 - ANS - Negative Ion
\Blast Furnace - ANS - Ingredients: 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 - ANS - Making: 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 - ANS - Positive Ion
\Changes of State - ANS - Solid --> Liquid - Melting
Liquid --> Solid - Freezing
, Liquid --> Gas - Boiling
Gas --> Liquid - Condensing
Solid --> Gas and Gas --> Solid - Sublimation
\Collecting Gases - ANS - Three 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 - ANS - Complete 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 - ANS - Between 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 - ANS - Isomer - same molecular formula but
different structural formula
Homologous Series - family of compounds with similar properties because they
have similar bonding.
\Diffusion - ANS - The spreading out of particles in a gas or a liquid. The lighter
the particles, the faster they diffuse. This is demonstrated by the experiment with
cotton wool soaked in ammonia solution at one end of a tube and cotton wool
soaked in HCl at the other end. The white cloud of ammonium chloride forms
closer to the hydrochloric end. Also to speed up diffusion, you can stir a liquid or
heat up the liquid or gas.
\Flame Test - ANS - Red shows lithium ions
Orange shows sodium ions
Lilac shows potassium ions
Brick Red shows calcium ions
\Gas - ANS - Particles are much further apart and there are almost no forces of
attraction between them.
\Giant Covalent Structures - ANS - Diamond - 4 strong bonds so very high melting
and boiling points. Cannot conduct electricity because no free ions to move and
carry charge. Insoluble. Silican dioxide has similar properties to diamond.
Carbon - 3 strong bonds but 4 ions so there's a free one to move and carry
charge so carbon can conduct electricity. Good lubricant as carbon is made up in
sheets which can slide over each other.
