A* REVISION NOTES | CHEMISTRY (C1-3)

Hope you find them useful, written from the Chemitry OCR Gateway course but will be useful for all GCSE courses.

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  • Created on: 30-05-09 13:51
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OCR Chemistry for GCSE Revision Notes C1-3
C1a Cooking
Some foods must be cooked: it kills harmful microbes with high temps, improves
the taste/texture, makes it easier to digest
The final product is different because of chemical reactions
Irreversible change, requiring energy, meat and eggs are high in protein, when an
egg is heated, protein molecules change shape ­ denaturing,
Potatoes are carbohydrates containing cellulose which forms cell walls around
starch, so uncooked potatoes are difficult to digest, cooking breaks down the
walls and releases the starch which becomes a gel by absorbing water
Baking powder is a raising agent (contains sodium hydrogencarbonate), this
decomposes when baked to produce CO2 which rises making `bubbles'
Limewater (calcium hydroxide) can be used to test CO2 as it turns cloudy
C1b Food additives
Preservative Reason for use E-numbe Used on...
r
Food colours Look more attractive E100-199 Sweets, soft drinks, jellies
Preservatives Preserve food E200-299 Jams, squashes
Antioxidants Slow down reaction with O2 E300-399 Meat pies, salad cream
Emulsifiers Keep ingredients mixed E400-499 Sauces, jams, salad cream, mayo
Flavour enhancers Improve flavour E600-699 Sweets, meat products
Additives have to be approved of safety, all approved additives have E-numbers
Emulsifiers: oil + water don't mix, adding an emulsifier makes an emulsion
(+shaking), emulsifier molecules have a hydrophilic head which has an ionic charge
and an hydrophobic tail, the heads repel each other due to their charge
Active or intelligent packaging is used to preserve foods, keeping out oxygen and
water helps stop bacteria growing, there are 2 ways of controlling free rad. no.'s
1:Oxygen scavengers: chemicals are placed in packaging that remove oxygen and
so prevent any oxygen reacting with it creating harmful free radicals
2:Antioxidants in the packaging combine with free radicals in the food before
they breakdown the food/packaging
Some film packaging lets oxygen in but ethene (which causes fruit to ripen) out
Cans can heat/cool their contents when opened and widgets in beer cans froth it
C1c Smells
Perfumes can be made from esters which are made by blending together natural oils
or made synthetically, esters are also used as flavouring agents and solvents
Mixtures of esters are very concentrated and are diluted by adding solvents
Perfumes are mainly used in everyday products like polishers and air refreshers
Organic acid + alcohol ester + water, (ethanoic acid + ethanol ethyl ethanoate)
Perfumes: need to evaporate - volatile, be non-toxic, non-irritant, insoluble in water
High volatility ­ weak attraction, high energy
-1-

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OCR Chemistry for GCSE Revision Notes C1-3
Esters can be used as solvents (solution = solvent + solute [that do not separate]),
they dissolve many substances which don't dissolve by water e.g. NVR
C1d Making crude oil useful
Crude oil formed when small sea creatures and plants died and buried, formed in high
temps. and pressures and in absence of air
Oil can be forced through cracks and low b.p. hydrocarbons evaporate forming pitch
Fractions (of similar b.p.…read more

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OCR Chemistry for GCSE Revision Notes C1-3
Exothermic/endothermic ­ give out/take in energy, bond forming is exothermic,
bond breaking is endothermic. Combustion is exothermic in O2
Calorimeter(metal can which measures the heat)
Energy = mass(kg) x s.h.c.(4.2 for water) x temp. change( C)
Energy per gram(J/g) = energy supplied(J) / mass of fuel burned(g)
C2a Paints and pigments
Synthetic dyes introduced a wider variety of colours and are now mainly used
Paints contain coloured pigments, a solvent and a binding medium.…read more

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OCR Chemistry for GCSE Revision Notes C1-3
The crust is rocky, the mantle is cold and rigid nearer the crust but less rigid nearer
the core (where convection currents can move molten rocks), the outer core is
liquid, and the inner core is solid.…read more

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OCR Chemistry for GCSE Revision Notes C1-3
steam cooled to form oceans, and some of the CO2 dissolved into the oceans. 3.
Much later simple plant life converted CO2 by photosynthesis; ammonia was
converted into nitrogen by bacteria which stayed there due to lack of reactivity.
A catalytic converter can be fitted to exhausts to change CO + NO N + 2CO2
C2g Faster or slower (1)
Reactions can be sped up with a higher temp./conc.…read more

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OCR Chemistry for GCSE Revision Notes C1-3
Ionic lattices are held by positive ions which are electrostatically attracted to the ­ve
ions ­ a lot of energy is needed to pull ions apart ­ high m.p.…read more

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OCR Chemistry for GCSE Revision Notes C1-3
Aluminium is from the mineral bauxite in the form of aluminium oxide, aluminium is
extracted from the purified oxide by electrolysis: 2Al2O3 4Al + 3O2
It is dissolved in molten cyrolite because it is insoluble in water and has a high m.p.…read more

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