Science GCSE (P1,B1,C1) chemistry

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  • Mix oil and water to make an emulsion.
  • Emulsions are lots of droplets of one liquid suspended in another.
  • Emulsifiers bind together the 2 liquids to stop them separating in 2 separate liquids.
  • 2 parts: Hydrophilic head which is attracted to water and hydrophobic tail which hates water but likes oil.
  • Head goes in water while tail sticks in the oil to hold them together.
  • Examples: Mayonnaise, ice-cream and low fat spread. 
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Cooking and Chemical Change

  • Irreversible chemical change, so chemical structure in permanently changed.
  • Taste better and better texture when cooked.
  • Easier for the body to digest.
  • Kill off microbes.
  • Some foods are poisonous when raw and must be cooked to get rid of any poisons.
  • Examples: Eggs and meat are full of protein molecules which change shape when you heat them, this breaks some of the bonds to give it an edible texture and let it change shape. Its called denaturing.
  • Examples: Potatoes are plants so have rigid cellulose cell walls, Humans cannot digest cellulose so its difficult for us to get the contents. Cooking breaks this cell wall which also makes the starch grains soften and swell out. Result is potato is softer and easier to digest.
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Thermal Decomposition

  • Substance breaks down into simpler substances when heated.
  • Helped by a catalyst.
  • Only one substance to start with.
  • Baking powder is used in cakes, when it goes through this process, the carbon dioxide produced is what makes it rise.


Sodium hydrogencarbonate - Sodium Carbonate + Carbon dioxide + Water

2NaHCO3 - Na2CO3 + CO2 + H2O

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  • Can be natural or artificial
  • Esters generally smell pleasant so are used for perfumes.
  • Esters are common in nature, like apples and jasmine, these are natural esters.
  • Can be manufactured synthetically to use as perfumes or flavourings.
  • Esters are made by mixing alcohol with a carboxylic acid.

Need to know:

Acid + Alcohol - Ester + Water

Need the following properties:

  • Highly volatile so it evaporates easily
  • Non toxic
  • Doesn't react with water
  • Doesn't irritate the skin
  • Insoluble in water so it doesn't wash off.

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Perfume/Cosmetics testing

  • New cosmetics and perfumes need to be tested so we know they are safe for use on humans.
  • First they are tested with a computer model, then on a mammal, which is controversial as many people believe it is wrong to put animals in potential danger.
  • Animals testing largely banned in the EU.
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Kinetic theory and forces between particles

  • Solids - Very strong forces of attraction between particles, holds them in position (rigid lattice arrangement), Particles vibrate around their positions, the hotter they get the more they vibrate.
  • Liquids - Some force of attraction between particles but although they are free to move past each other they tend to stick. Constantly moving in a random motion. Hotter liquid is, the faster they move.
  • Gases - Almost no forces of attraction between them, they are free to move in straight lines and only interact when they collide. Don't keep any shape but fill a container, when they bounce of container walls it exerts the pressure. Gases expand when heated therefore increasing the pressure.
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  • When a liquid is heated, the heat energy goes to the particles, making them move quicker.
  • Some particles move faster than others.
  • Fast moving particles at the surface will overcome the forces of attraction from the other particles and escape.
  • This is evaporation!
  • Volatility is how easily it evaporates.
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Solutions - What it is

  • Mixture of solvent and solute.
  • When you add a solid (solute) to a liquid (solvent) the bonds holding the solute molecules together sometimes break and the molecules can then mix with the molecules of the liquid. This is dissolving. Whether the bonds break or not depends on how strong the intermolecular forces between the two substances are.
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Solutions - Definitions

  • Solution - Mixture of solvent and solute that doesn't separate out.
  • Solute - Is the substance being dissolved.
  • Solvent - Is the liquid it's being dissolved into.
  • Soluble - It will dissolve.
  • Insoluble - It will not dissolve.
  • Solubility - Measure of how much will dissolve.
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Insoluble and Insolubility

  • Nail varnish doesn't dissolve in water, this is because the nail varnish molecule are more strongly attracted to each other than they are to water molecules. Also vice versa - water molecules are more strongly attracted to each other than they are to the varnish molecules.
  • But it is soluble in nail varnish remover (acetone), this is because the molecules of the acetone are more strongly attracted to the nail varnish than they are to other acetone molecules. 
  • So the solubility of of a substance depends on the solvent used.
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Paints and pigments

  • Pigments give paint their colours. 
  • Binding medium sticks the paint to the surface of whatever your painting. It also hold the paint together.
  • The solvent thins the paint and makes it easier to spread.
  • Paints are colloids - where the solid particles are so tiny they don't settle, they are just suspended in the other substance (dispersed) but not dissolved. So in a paint, that solid is the pigment.
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Different paints - Oil and water based

  • Water based - Emulsion paints where the solvent is water, the binding medium is an acrylic or vinyl acetate polymer.
  • Dries when the solvent evaporates leaving the binding medium and the pigment as a thin solid film. Dries quite quickly.
  • Emulsion paints don't produce harmful fumes so are good for painting indoors.
  • Oil based - This time the binder is oil and the solvent is an organic compound that dissolves oil.
  • Dry in 2 stages: Solvent evaporates then the oil is oxidized by the air before it turns solid. So they take longer to dry.
  • Oil paints are glossy, waterproof and hard wearing, but the solvents used to make them usually produce harmful fumes. They are best for painting things like outside walls or metalwork.
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Thank You..i have an excam cmming up...this litterally covers everything :D THANK UU SOO MUCH 

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