AQA C2 Revision notes

Good summary notes for Additional Chemistry

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  • Created on: 06-01-11 19:43
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Atoms, Molecules and Ions.
AN ATOM is the smallest particle of an element. They cannot be split into smaller particles in
chemical reactions. Iron is made of iron atoms (Fe). Sulphur is made of sulphur atoms (S)
A MOLECULE is a small group of atoms joined together.
The atoms may be the same (e.g. O2) or different (e.g. H2O). The chemical formula shows
the number and type of atoms present. Non-metal compounds are made of molecules:
Carbon dioxide contains CO2 molecules
Methane (natural gas) contains CH4 molecules
AN ION is an atom or group of atoms with an electrical charge (+ or -). Metal compounds
such as sodium chloride or copper sulphate contain ions.
Sodium chloride is made of Na+ and Cl- ions
Copper Sulphate is made of Cu2+ and SO42- ions
Note that metals form positive ions while non-metals form negative ions.
A solid is represented by (s). e.g. H2O(s) is ice.
A liquid is represented by (l) e.g. Fe(l) is molten iron.
A gas is represented by (g) e.g. H2O(g) is steam.
A solution in water is represented by (aq). Salt dissolved in water is NaCl(aq).
You should remember that the common gases are diatomic (have 2 atoms in each
molecule). These are Oxygen O2; Hydrogen H2; Nitrogen N2; and Chlorine Cl2.
Elementary Particles
Atoms are made up of smaller particles called protons, neutrons and electrons.
The protons and neutrons cluster together in a small nucleus at the centre of the atom
while the electrons orbit the nucleus.
The main properties of the particles are:
Particle Mass Charge
ELECTRON Very Small -1
Every element has an atomic number, which is the number of protons in the nucleus.
Atoms are neutral, so that the number of electrons is the same as the number of
The mass of an atom is almost entirely made up of protons and neutrons, which have the
same mass as each other (the mass of electrons can be ignored).
These relations can be summarised as:

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Atomic Number Protons Electrons Neutrons Mass Number
Na 11 11 11 12 23
C 6 6 6 6 12
U 92 92 92 146 238
Electronic Structure
The electrons orbit the nucleus in 'shells'. These can hold the following numbers of
the innermost shell can contain up to 2 electrons
the next shell can contain up to 8 electrons
the next shell can contain up to 8 electrons (although this can be expanded up to 18)
Fluorine has atomic number 9.…read more

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They do not conduct electricity
Simple molecular substances are nearly always non-metallic elements or their compounds.
e.g. Water (H2O), Iodine (I2), Carbon dioxide (CO2), Sugar (C12H22O11).
Giant Covalent Substances
In these substances, strong covalent bonds join atoms together in large numbers to make
giant structures. Sand (silicon dioxide) is one example, diamond and graphite (both forms of
carbon) are others are others. Because the bonds between all the atoms are very
1) They have very high melting points.…read more

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Mg(NO3)2 = 24 + (14 + 3x16)x2 = 148
Percentage Calculations
If you need to find the percentage of an element E in a compound, you use tormula
Percentage = Ar of E x No of atoms of A x 100
Mr of compound
e.g.…read more

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What mass of carbon dioxide is obtained by burning 3g of C2H6?
2C2H6 + 7O2 = 4CO2 + 6H2O
Mr: C2H6 = 30, CO2 = 44
Answer = 3 x (4x44) = 0.05 x 176 = 8.8g
Atom Economy
This is given as Formula Mass of all molecules of Useful Product x 100
Formula Mass of all molecules of Reactants
Eg.…read more

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If a reaction is exothermic in one direction, it will be endothermic in the other direction and
the amount of heat given out by the exothermic reaction will be equal to the amount of
heat taken in by the endothermic reaction.
(Blue) (White)
If the hydrated copper sulphate is heated, it turns white as the water is given off.…read more

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Manufacture of Ammonia
1) Ammonia is made from nitrogen and hydrogen. Nitrogen is separated from air, while
hydrogen is obtained by the cracking of oil.
2) The equation for the reaction is:
Nitrogen + Hydrogen Ammonia (exothermic)
N2 + 3H2 2NH3
3) The conditions needed for the reaction are 200 atmospheres pressure, 450oC and an iron
a) The pressure brings the molecules closer together, so that they react faster and
also give a greater yield of ammonia since the forward reaction is encouraged.…read more

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Aluminium Oxide Cracking of Oil
Iron Manufacture of
Vanadium Pentoxide Manufacture of sulphuric acid.
Most of these catalysts are solid substances, used to catalyse reactions between gases.
They do this by
allowing the gas molecules to collect on their surface where they are close enough to react
Catalysts are very valuable in chemical industry, since they can be reused and they provide a
much cheaper way of speeding up a reaction than heating, so providing cheaper goods.…read more

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The rate of this reaction can be measured by seeing how much hydrogen gas is given off in
one minute. This rate can be increased by:
1) Raising the temperature of the reaction.
2) Using more concentrated sulphuric acid.
3) Using powdered zinc rather than lumps.
4) Adding some copper, which acts as a catalyst.
The rate of a reaction can be measured and followed on a graph, e.g.…read more

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Energy changes in reactions
Reactions which give out energy are called Exothermic. They cause the temperature to rise.
Many reactions are exothermic, including all burning (combustion) reactions
e.g. 2Mg + O2 = 2MgO
Reactions which take in energy are called Endothermic. They may cause the temperature to
fall. Thermal decompositions are always endothermic
e.g. CaCO3 = CaO +CO2
Some reactions require an initial input of energy to start the reaction (called the activation
energy) but are exothermic. E.g. the match to light the fire.…read more


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