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breathable polymers

Nylon is tough, lightweight, keeps water and keeps ultra violet light out but does not let water vapour through. This means that sweat condenses and makes the wearer wet and cold inside their jacket.

GORE-TEX has all the properties of nylon but is also breathable, so it is worn by many active outdoor people. Water vapour from sweat can pass through the membrane but rainwater cannot.

GORE-TEX material is waterproof yet breathable;

it is made from a PTFE (polytetrafluoroethene/ polyurethane membrane

The holes in PTFE are too small for water too pass through but are big enough for water vapour to pass through.

PTFE is too fragile on its own and so it is laminated onto nylon to produce a stronger fabric,

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disposal of polymers

Scientists are developing new types of polymers;

Polymers that dissolve & biodegradable polymers

Research into new polymers is important because there are enviromental and economic issues with the use of existing polymers

-disposal of non-biodegradable polymers means landfill sites get filled quickly

-landfill means wasting land that could be valuable for other purposes

-disposal by burning waste plastics makes toxic gases.

- disposal by burning or using landfill sites wastes the crude oil used to make the polymers,

- it is difficult to sort out different polymers so recycling is difficult

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Stretchy polymers and rigid polymers

Atoms in polymers are held together by strong covalent bonds

The properties of plastics can be related to simple models of their structure.

- plastics that have weak intermolecular forces between polymer molecules have low melting points and can be stretched easily as the polymer molecules can slide over each other.

- plastics that have strong forces between the polymer molecules (covalent bonds or cross-linking bridges) have high melting points, cannot be stretched and are rigid.

intermolecular forces are weak forces of attraction between molecules and are not as strong as covalent bonds within molecules.

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Proteins and carbohydrates

Protein molecules in eggs and meat permanently change shape when eggs and meat are cooked.

This changing of shape is called 'denaturing'

The texture of egg or meat changes when it is cooked because the shapes of the protein molecules change permanently.

Potato is a carbohydrate which is easier to digest if it is cooked because;

-the starch grains swell up and spread out

- the cell walls rupture resulting in the loss of their rigid structure and a softer texture is produced.

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Baking powder

Baking powder is sodium hydrogencarbonate

When it is heated it breaks down (decomposes) to give carbon dioxide.

The word equation for the decomposition of sodium hydrogen carbonate is;

sodium hydrogencarbonate = sodium carbonate + carbon dioxide +water

The balanced symbol equation for the decomposition of sodium hydrogencarbonate is;

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Emulsifiers are molecules that have a water-loving (hydrophilic) part and an oil- or fat-loving (hydrophobic) part.

The oil- or fat-loving part (the hyrdrophobic end) goes into the fat droplet

Emulsifiers help to keep oil and water from seperating;

the hydrophilic end bonds to the water molecules

The hydrophobic end bonds with the oil or fat molecules

The hydrophilic end is attracted to the water molecules which surround the oil, keeping them together.

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Alcohols react with acids to make an ester and water

alcohol + acid = ester + water

Esters are used to make perfumes

An ester can be made using a simple experiment

- the acid is added to the alcohol and heated for some time.

- The condenser stops the gas from escaping and helps to cool it down again, so that it can react more.

- the condenser allows the reation to go on for longer.

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Perfume properties&solutions

A perfume must have certain properties, it must;

-evaporate easily so that the perfume particles can reach the nose.

-be non-toxic so it does not poison you

-not react with water so the perfume does not react with perspiration

-not irritate the skin so the perfume can be put directly onto the skin.

-be insoluble in water so it cannot be washed off easily.

A solution is a mixture of solvent and solute that does not seperate out.

Esters can be used as solvents.

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The volatility, or ease of evaporation of perfumes can be explained in terms of kinectic theory.

-In order to evaporate, particles of a liquid need sufficient kinetic energy to overcome the forces of attraction to other molecules in the liquid.

- only weak attractions exist between particles of the liquid perfume so it is easy to overcome these attractions as they have sufficient kinetic energy.

Water will not dissolve nail vanish colours;

-the attraction between the water molecules is stronger than the attraction between the water molecules and the nail varnish molecules,

-the attraction between the nail varnish molecules is stronger than the attraction between water molecules and the nail varnish molecules.

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Paint is a colloid where the particles are mixed and dispersed with particles of a liquid (binding medium) but are not dissolved.

The components of a colloid will not seperate because the particles are scattered or dispersed throughout the mixture and are sufficiently small so as not to settle at the bottom.

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Paint drying

Most paints dry because ;

-paints are apllied as a thin layer

-the solvent evaporates

Emulsion paints are water-based paints that dry when the solvent evaporates.

Oil paints dry because;

-the solvent evaporates

-the oil is oxidised by atmospheric oxygen.

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Thermochromic pigments

Thermochromic pigments change colour at different temperatures, Thermochromic pigments are used;

-as thermometers because they change colour when the temperature of a body or the temperature of a fridge rises.

-in the manafacture of some cups- the colour changes to show when they are ot.

-in electric kettles to keep users safe when boiling water

-in babies' spoons and bath toys, to warn if the spoon or toy is too hot to give to a baby.

Thermochromic pigments can be added to acrylic paints to make even more colour changes. If a blue thermochromic pigment which turns colourless when hot is added to yellow acrylic paint, the paint will appear green when cool and yellow when hot.

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Phosphorescent pigments

Phosphorescent pigments glow in the dark because;

-they absorb and store energy

-they release the energy as light over a period of time

Phosphorescent pigments are much safer then the older, alternative radioactive paints.

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