C1 Revision

Topic 1 The fundamental ideas in chemistry

The periodic table of elements Everything is made from elements The periodic table of elements shows us metals (left) and non-metals (right) Each element has a symbol… Sodium is ‘Na’ and Carbon is ‘C’ Each group has similar chemical properties

Atoms A particle of an element is called an atom e.g. a carbon atom, a sodium atom Atoms have the same amount of positive and negative charges so they are neutral Type of sub-atomic particle Relative charge Proton +1 (positive) Neutron 0 (neutral) Electron -1 (negative)

Mass number Atomic number Elements in the periodic table are arranged in order of their atomic number atomic number = number of protons No. of protons = no. of electrons (protons and electrons cancel each other’s charges out) The mass number = no. of protons + neutrons No. of neutrons = mass no. – atomic no.

Arrangement of electrons Electrons are arranged around the nucleus of atoms in shells The first shell can hold up to 2 atoms The second shell can hold up to 8 atoms The third shell can hold up to 8 atoms Then the fourth shell fills up Lithium 2,1

Arrangement of electrons Fluorine 2,7 Chlorine 2,8,7 Calcium 2,8,8,2

Electrons and the periodic table Elements in the same group all have the same number of electrons in their outer shell This means that they share similar properties Group 1 elements all have 1 electron in the outer shell – they are all very reactive Group 0 elements (noble gases) have full outer shells – they are unreactive

Group 1 – alkali metals Lithium, sodium and potassium all react violently with water They form salts which are alkaline in pH Lithium + water  lithium hydroxide + hydrogen Sodium + water  sodium hydroxide + hydrogen potassium + water  potassium hydroxide + hydrogen

Forming compounds When atoms of different types of elements join together they form ‘compounds’ Sometimes atoms react by transferring electrons – this happens when metals react with non-metals and forms ions Metals lose electrons and become positive ions (+) Non-metals gain electrons – negative ions (-) These ions are attracted to each other and form an ionic bond

Ionic bonds

Forming molecules Sometimes atoms react by sharing electrons – this happens when non-metals react with non-metals This is called covalent bonding

Chemical formulae This tells us the number of atoms in a compound or molecule CH4 H2O MgCl2 CaCO3 Fe2O3 2C2H5OH - 1 x Carbon, 4 x Hydrogen - 2 x Hydrogen, 1 x Oxygen - 1 x Magnesium, 2 x Chlorine - 1 x Calcium, 1 x Carbon, 3 x Oxygen - 2 x Iron, 3 x Oxygen - 4 x Carbon, 11 x Hydrogen, 1 x Oxygen

calcium carbonate  calcium oxide + carbon dioxide Chemical equations These show us the reactants (the substances we start with) and the products (the substances made) calcium carbonate  calcium oxide + carbon dioxide CaCO3  CaO + CO2 The equation is balanced – the same number of atoms are going in and are coming out of the reaction The total mass of the products formed in a reaction is equal to the total mass of the reactants

Topic 2 Limestone and building materials

Calcium carbonate  calcium oxide + carbon dioxide Limestone Limestone is a rock made mainly of calcium carbonate (CaCO3) It was formed from the remains of animals millions of years ago and can be quarried Limestone can be heated with clay to make cement Cement is mixed with sand to make mortar Cement is mixed with water, sand and crushed rock to produce concrete Heating limestone breaks it down – this is thermal decomposition Calcium carbonate  calcium oxide + carbon dioxide CaCO3  CaO + CO2

Magnesium carbonate  magnesium oxide + carbon dioxide Carbonates Buildings made of limestone are damaged by acid rain When this happens, carbon dioxide is given off Carbon dioxide turns limewater cloudy The carbonates of magnesium, copper, zinc, calcium and sodium can be thermally decomposed too They always form a metal oxide and carbon dioxide e.g. Magnesium carbonate  magnesium oxide + carbon dioxide MgCO3  MgO + CO2

Uses of calcium oxide When limestone is thermally decomposed it produces calcium oxide When calcium oxide is added to water it produces calcium hydroxide Calcium hydroxide can be filtered to produce limewater Calcium hydroxide is an alkali. It can be used to neutralise acids. It is used by farmers to neutralise acidic soil, and to neutralise acidic industrial gases.

Topic 3 Metals and their uses

Extracting metals Metals are found in the Earth’s crust They are often chemically combined with other elements – this is called the ore Whether it is worth extracting a metal depends on: 1. How easy it is to extract it from its ore 2. How much metal the ore contains

Transition metals

Extracting metals electrolysis carbon reduction Other methods The way we extract a metal depends on its place in the reactivity series Most reactive Least reactive Potassium Sodium Calcium Magnesium Aluminium Carbon Zinc Iron Tin Lead Copper Silver Gold Platinum electrolysis carbon reduction Other methods

Carbon reduction A more reactive metal will displace a less reactive metal from its compounds Many metals combine with oxygen – carbon will also displace less reactive metals from their oxides when heated with them Metal oxide + carbon  metal + carbon dioxide Lead oxide + carbon  lead + carbon dioxide 2PbO + C  2Pb + CO2

Iron (III) oxide + carbon  iron + carbon dioxide Iron ore contains iron combined with oxygen Iron is extracted using carbon reduction It is heated in a blast furnace Iron (III) oxide + carbon  iron + carbon dioxide Iron straight from the blast furnace still contains some impurities (it is about 96% iron) – it is very brittle and is called cast iron. It can be used to mould different shapes Removing the impurities gives us pure iron – this is too soft for most uses

Iron To make iron useful we can add small amounts of other elements A metal that is mixed with other elements is called an alloy Steel is an alloy of iron Carbon steel contains between 0.03% and 1.5% carbon Low carbon steels are easily shaped High carbon steels are very strong Iron with chromium and nickel makes stainless steel

Aluminium Aluminium is a very low density metal It can be alloyed with other elements to make it very strong It cannot be extracted from its ore by carbon reduction because it is more reactive than carbon It is extracted using electrolysis instead – an electric current is passed through molten aluminium oxide at high temperatures to break it down Electrolysis is very expensive because lots of energy is needed – this is why we recycle aluminium

Titanium Titanium is very strong and has a very high melting point It is used for jet engine parts, replacement hip joints and as nuclear reactor parts It cannot be reduced using carbon because it is more reactive It is reduced using sodium or magnesium, but this process is very complicated and has lots of steps, which means the titanium is very expensive

Copper (I) sulfide + oxygen  copper + sulphur dioxide Pure copper is a good conductor of electricity, does not react with water and can be shaped easily Copper can be removed from its ore by smelting This involved heating it in a furnace: Copper (I) sulfide + oxygen  copper + sulphur dioxide

Copper The copper produced is purified using electrolysis This involves passing an electrical current through a copper solution

Copper Copper-rich ores are running out New methods are used to extract copper from low grade ores Phytomining – using plants to extract copper Bioleaching – using bacteria to extract copper 20% of our copper comes from bioleaching

More alloys Bronze = copper + tin this is tough with resistant to corrosion (used to make statues) Brass = copper + zinc this increases the strength of copper but is still malleable (used to make musical instruments) Gold can be alloyed to increase its strength There are over 300 aluminium alloys with different properties

Topic 4 Crude oil and fuels

Crude oil Crude oil is a fossil fuel that was formed millions of years ago from the remains of sea creatures It is a dark, thick liquid containing a mixture of lots of different chemical compounds We separate the different compounds by fractional distillation This involves separating the different fractions depending on their boiling points

Crude oil Crude oil contains compounds made of only hydrogen and carbon – hydrocarbons Most of the hydrocarbons are alkanes The general formula for alkanes is CnH(2n+2) Alkanes are saturated hydrocarbons because they are full – no more bonds can be made

Alkanes Methane CH4 Ethane C2H6 Propane C3H8 Butane C4H10

Properties of hydrocarbons Chain length: Boiling point: Low High Volatility (tendency to turn into gas): Viscosity (how easily it flows): Low (very runny) High (very thick) Flammability (how easily it burns):

Fractional distillation of crude oil

Propane + oxygen  carbon dioxide + water C3H8 + 5O2  3CO2 + 4H2O Combustion When hydrocarbons are burned in air they release energy – this ‘oxidises’ the hydrogen and the carbon in the fuel (oxygen from the air is added) This is called complete combustion Propane + oxygen  carbon dioxide + water C3H8 + 5O2  3CO2 + 4H2O The carbon dioxide released can cause global warming Incomplete combustion happens when there is not enough oxygen – carbon monoxide (CO) is produced instead of carbon dioxide (CO2) – this is a poisonous gas

Pollution from hydrocarbons Fossil fuels contain sulfur When they are burned it releases sulfur dioxide This is a poisonous gas that causes acid rain High temperatures inside car engines can cause nitrogen and oxygen to react forming nitrogen oxides These are poisonous and can trigger asthma and cause acid rain Diesel engines can release particulates – these are tiny particles of carbon released into the air – these can cause global dimming

carbon monoxide + nitrogen oxides  carbon dioxide + nitrogen Cleaner fuels A catalytic converter can be fitted to a cars exhaust to reduce the amount of carbon monoxide and oxides of nitrogen released carbon monoxide + nitrogen oxides  carbon dioxide + nitrogen In power stations, sulfur dioxide can be removed from waste so it isn’t released into the atmosphere Sulfur impurities can also be removed from fuels before combustion

Biofuels Fossil fuels are running out – an alternative is biofuels made from plant or animal products Biodiesel is made from oils from plants It produces less pollution than diesel Using land for biodiesel plants instead of food crops could cause problems Ethanol is made from fermented sugar cane Ethanol can be mixed with petrol to save money Ethanol still gives off carbon dioxide when burned, but the sugar cane plant absorbs CO2 for photosynthesis

Topic 5 Other useful substances from crude oil

Cracking After fractional distillation of crude oil, we are left with lots of less useful long-chain hydrocarbons Long-chain hydrocarbons can be broken down in a process called cracking This involves heating the fraction until it vapourises then passing it over steam or a hot catalyst

Hexane  butane + ethene Cracking hexane (800°C + hot catalyst) Hexane  butane + ethene C6H14  C4H10 + C2H4

Testing alkanes and alkenes Bromine water reacts with alkenes and forms a colourless solution Unsaturated hydrocarbon + bromine water  colourless solution The double bond opens up and reacts Bromine water remains orange in alkanes Saturated hydrocarbon + bromine water  orange solution The hydrocarbon cannot make any more bonds and doesn’t react

Polymers Hydrocarbon molecules can be used to make plastics Small molecules are called monomers Lots of monomers joined together make polymers

Polymerisation Chloroethene monomers A section of poly chloroethene (PVC)

A repeating unit of poly chloroethene (PVC) Polymers A repeating unit of poly chloroethene (PVC)

New polymers New plastics with special properties are being developed Dental fillings, waterproof fabrics and light sensitive plasters are made with special polymers Smart polymers such as shape memory polymers ‘remember’ their original shape and will return to it when heated e.g. stitches closing a wound using body heat

Plastic waste Many polymers are not biodegradable – this means microorganisms cannot break them down New biodegradable polymers have been developed using starch and plant products that microorganisms can break down This reduces the amount of plastics in landfills

Ethanol This is the type of alcohol found in alcoholic drinks Its formula is C2H5OH Ethanol can be made by fermentation of sugar from plants with yeast Glucose (sugar)  ethanol + carbon dioxide C6H12O6  2C2H5OH + 2CO2 Ethanol can also be produced by reacting ethene (from cracking crude oil) with steam A catalyst is used to speed up the reaction Ethene + steam  ethanol C2H4 + H2O  C2H5OH

Topic 6 Plant oils and their uses

Vegetable oil Some fruits, seeds and nuts are rich in oils that can be extracted The plant material is crushed and the oil is removed by pressing or distillation Water and other impurities are removed Vegetable oils provide nutrients and have a high energy content They are important foods and can be used to make biofuels

Unsaturated oil + bromine water  colourless solution Vegetable oil Vegetable oils contain hydrocarbons Unsaturated oils with C=C bonds can be detected using bromine water – they decolourise it Unsaturated oil + bromine water  colourless solution Vegetable oils have higher boiling points than water Foods can be cooked at higher temperatures than by boiling Food cooks faster and has different flavours Food cooked in vegetable oil releases more energy when it is eaten (increased calorie content)

Emulsions Oil does not mix with water An emulsifier is a special molecule that can be used to mix them and create an emulsion Emulsions include ice cream and mayonnaise Without an emulsifier, the oil and water would separate out into layers

Topic 7 Changes in the Earth and its atmosphere

Structure of the Earth The Earth is made up of many layers Crust: thin and rocky Mantle: flowing rock Core: mixture of nickel and iron (inner core = solid outer core = liquid) The Earth is made up of many layers The Earth is surrounded by the atmosphere

Tectonic plates The crust and mantle are broken up into large pieces (tectonic plates) They move a few centimetres per year due to convection currents in the mantle Earthquakes are caused when plate boundaries meet and push together

The modern atmosphere The Earth’s atmosphere has been the same for about 200 million years

The early atmosphere There are lots of theories One suggests that there was intense volcanic activity about 4.5 billion years ago when the Earth formed This released carbon dioxide, water vapour and nitrogen gas – this formed the first atmosphere The water vapour condensed and fell as rain, this formed the first oceans When life evolved plants released oxygen The amount of oxygen in the atmosphere increased and animals could evolve

Carbon Most of the carbon dioxide from the Earth’s early atmosphere has been taken up by plants, which were eaten by animals, which were turned to sedimentary rocks This means that most of the carbon is ‘locked’ in rocks and in fossil fuels Carbon dioxide also dissolved in oceans Over the past 200 million years the amount of carbon dioxide in the atmosphere has not changed much

The carbon cycle Using fossil fuels is increasing the amount of carbon in the atmosphere again