GCSE Chemistry OCR Gateway Higher Tier C4, C5 and C6 Complete Notes

Chemistry OCR Gateway Higher Tier C4, C5 and C6 Complete Notes

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  • Created on: 14-06-12 14:38
Preview of GCSE Chemistry OCR Gateway Higher Tier C4, C5 and C6 Complete Notes

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Chemistry C4-Chemical Economics
The pH scale and universal indicator:
Example
pH
strong alkali 14 drain cleaner
13 bleach
12 soapy water
11 ammonia
10 milk of
magnesia
9 baking powder
8 sea water
neutral 7 pure water
6 saliva
5 black coffee
4 acid rain
3 vinegar
2 lemon juice
1 stomach acid
strong acid 0 battery acid
An indicator is just a dye that changes colour
o The dye in indicator changes colour depending on the pH
o Universal indicator is a very useful combination of dyes which gives the colours shown
above.
o It is useful for estimating the pH of a solution
An acid is a substance with a pH of less than 7. Acids form H+ ions in water.
A base is a substance with a pH greater than 7.
An alkali is a base that dissolves in water. Alkalis form OH- ions in water.
Neutralisation reaction:
o Acid + base -> salt + water
o H+ + OH- -> H2O
Industrial use of sulphuric acid:
o Sulphuric acid is used in car batteries
o In the manufacturing industry to make fertilisers and detergents

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It can also be used to clean metal surfaces. As a metal surface is usually covered with a
layer of insoluble metal oxide. Sulphuric acid reacts with these, forming soluble metal
salts which wash away.…read more

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Liquid: you lose a bit of the filter paper as it always stays wet
Solid: some will get left behind on the filter paper
Transferring liquids- some liquid will also get left behind on the inside surface on
the old container. (the beakers are always left wet even when you have
transferred the liquid).
Fertilisers:
o Fertilisers provide plants with the essential elements for growth:
The three main essential elements in fertilisers are nitrogen, phosphorus and
potassium.…read more

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The reaction is reversible- not all nitrogen and hydrogen will convert into
ammonia
The nitrogen and hydrogen which don't react are recycled and passed through
again so none is wasted.
o Industrial Conditions:
Pressure= 200 atmospheres
Temperature = 450oC
Catalyst= Iron
o Because the reaction is reversible, compromises have to be made:
Higher pressures favour the forward reaction- so the pressure is set as high as
possible to give the best % yield- without making the plant too expensive to
build.…read more

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High temperatures usually work the best when washing clothes. As the high
temperatures melt greasy dirt deposits, so your detergent can break up and
remove the stain more easily.
But some natural fabrics shrink and some artificial fabrics quickly lose their shape
if they're washed at too high a temperature.
Some dyes will also run at high temperatures. Brightly coloured clothes can
quickly fade.
Biological detergents have enzymes in them.…read more

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Dry-cleaning can also be used for clothes that have a stain that won't dissolve in
water or detergent. Paints, varnishes and other organic chemicals often dissolve
in an organic dry-cleaning solvent.
Dry cleaning works as the solvent is strongly attached to the oily molecules in the
stain. The intermolecular bonds between the stain molecules break and are
replaced by bonds with the solvent. The stain dissolves.…read more

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This also makes graphite slippery and so it's an ideal lubricating material.
Graphite has got a high melting point as the covalent bonds need loads of
energy to break.
Since only three out of each carbon's four bonds are used in bonds, there are
lots of spare electrons. This means that graphite conducts electricity- it is used
for electrodes in electrolysis.…read more

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Bromide ions will produce a cream precipitate
Iodide ions will produce a pale yellow precipitate
Eg/
AgNO3 + NaI -> Agl + NaNO3
o Clean water:
o Some communities in developing countries can't get safe water to drink
o They may have to walk for miles to fetch water from sources where it may be
contaminated
o Dirty water can carry dangerous microbes which can cause serious diseases
o Giving a community a clean water source can save lives
o Distilling sea water:
o In…read more

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Divide by the AR of 44.8/56=0.8 19.2/16=1.2
the element
4. Multiply by 10 8 12
Divide by 4 2 3
Empirical formula: Fe2O3
Electrolysis:
o Electrolysis is the breaking down of a substance using electricity
o Electrons are taken away from ions at the positive electrode (anode) and passed by an
external circuit to the negative electrode (cathode) where they're given to other ions in
the electrolyte.…read more

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Question: Find the mass of lead liberated if 5 amps flows for 20 minutes during the
electrolysis of lead (II) chloride (PbCl2)
1. Write out the balanced half-equation for each electrode
Pb2+ + 2e- -> Pb 2Cl- -> Cl2 + 2e-
2. Calculate the number of faradays
First calculate amps X seconds= 5 x 20 x 60 = 6000 coulombs
Number of faradays= 6000/96000= 0.0625 F
3.…read more

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