Chemistry Revision notes C4, C5, C6 OCR 21st Century Science

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  • Created on: 23-01-13 22:24
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CHEMISTRY REVISION
Periodic table
All the elements on the Earth are on the Periodic Table.
They are arranged according to patterns in their properties e.g. The masses of their atoms
The relative atomic mass is the mass of an atom in relation to hydrogen e.g. Helium has an
atomic mass of 4 which means it has 4x the mass of hydrogen
Each period starts with a metal and ends with a non-metal
Alkali metals
The alkali metals (Group 1 in the periodic table) are Lithium, Sodium,
Potassium, Rubidium, Caesium and Francium. This is in order of reactivity from
the least to most reactive.
Alkali metals are different from other metals as they are not very dense and
can be cut easily and they produce an alkali reaction with water.
They oxidise in the air and in water they make hydrogen and hydroxide.
They are kept in oil to make sure that it does not react with oxygen in the air
They all have low densities
The more reactive the metal the less melting and boiling point they have
which is why melting and boiling point of alkali metals do down the higher the
period number.
Their surfaces shiny when freshly cut but tarnish rapidly in moist air due to reaction with
oxygen
React with water to form hydrogen and an alkaline solution of a hydroxide with the formula
MOH (M represents Li, Na, K etc.)
React vigorously with chlorine to form colorless, crystalline salts with the formula MCl (M
represents Li, Na, K etc.)
4 Alkali metal + Oxygen2 2 Alkali metal2Oxygen
Example: 4Li+O2 2Li20
2 Alkali metal+2H20 2Alkali metal0H + H2
Example: 2Na+2H20 2NaOH + H2

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Anyone using a corrosive substance should wear gloves and eye protection, such as goggles
or a face shield.
Anyone using an irritant substance should wear eye protection such as goggles, and they
should take care to wash any spills off their skin immediately.
Anyone who uses a toxic chemical needs to take great care. They should wear gloves and
eye protection, and they may wear a mask over their mouth and nose, or handle the chemical
in a fume cupboard.…read more

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Melting point 63 degrees
Boiling point 760 degrees
When reacting with oxygen it makes Potassium oxide.
When burning it creates a lilac pink flame
When reacting with water it produces Potassium Hydroxide + Hydrogen and makes little
sparks. The water doesn't change colour. The reaction is more vigorous than the Lithium and
Sodium.
When reacting with Chlorine it produces Potassium Chloride (low sodium salt) and makes a
lilac pink flame and a white (potassium chloride) residue.…read more

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Cl2 + 2NaBr 2NaCl + Br2. As chlorine is more reactive than bromine it displaces bromine to
make sodium chloride and bromine is left on its own.
Iodine however cannot displace Bromide as it is not as reactive so I2 + 2NaCl ---àNo reaction
Chlorine is more reactive then iodine as we can use iodine as a disinfectant but chlorine
cannot be used on our skin.…read more

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Ionic Bonding:
Transferring electrons.
A shell with just one electron wants to get rid of it.
o Atoms in groups 1,2 and 3 all have just 1,2 or 3 electrons which they want to get rid
of.
o When they do, ions really want to bond.
A shell with 1, 2 or 3 too little electrons really want to gain some.…read more

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In aqueous solutions as well as the ions from the solute there are H+ ions and OH- ions.
Sometimes it's easier to discharge the ions from the water instead of the ones from the
solute. This means hydrogen could be produced from the cathode and oxygen at the
anode.
o In molten salts there is only one source of ions. Positive metal cations are reduced (they
gain electrons) to atoms at the cathode. Negative anions are oxidised (they lose
electrons) to atoms at the anode.…read more

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Then you need to repeat the whole experiment a few times, making sure you
get approximately that same answer each time.
o Single indicators are used for titrations:
Universal indicator is used to estimate the pH of a solution because it can turn a
variety of colours. Each colour indicates a narrow range of pH values. It is made
from a mixture of different indicators. The colour gradually changes red in acidic
solution to violet in alkaline solutions.…read more

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Iron I
Tin Think
Lead Love
Copper Can
Silver Stop
Gold Global
Platinum Peace
o The further apart the metals are in the reactivity series, the higher the temperature
change in the displacement reaction.…read more

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The earth's lithosphere is made of a mixture of minerals.
o Made of a mixture of minerals often containing silicon, oxygen and aluminium.
o Different rocks contain different elements.
Silicon dioxide forms a giant covalent structure.
o Giant covalent structures contain no charged ions.
o They are very hard, high melting points; they never conduct electricity and are
usually insoluble.
Some minerals are expensive, and the rarer the more valuable.
Chemicals in the Biosphere: (anything that's alive)
Living things all share the same building blocks.…read more

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Metallic bonds are strong so it takes a lot of energy to break them.
Synthesising Compounds:
Seven Stages involved in chemical synthesis. When making these chemicals in chemical
synthesis you have to choose the right process.
o Choosing the reaction:
Neutralisation for a salt?
Thermal decomposition ­ make a compound into simpler substances.
Precipitation ­ An insoluble liquid is formed when two solutions are mixed.…read more

Comments

lisa linsdell

Comprehensive revision notes for these three topics. Contains a neat little memory aid for the reactivity series and redox reactions, Do watch out for the odd spelling and grammar errors, e.g larger surface area not higher surface area. Overall, a good aid for revision

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