C1f COOKING Cooking is a chemical change. Eggs, fish and meat are sources of protein. When protein molecules are cooked, they change shape. This is called denaturing. Potatoes contain starch. It is difficult to digest. When potato is cooked, the cell walls break and it gets softer. The starch grains are released and absorb water so they swell up Changes in cooking Appearance and texture changes. These are irreversible. KEY WORDS: Chemical change Denaturing Protein Thermal decomposition Baking powder is sodium hydrogen carbonate When sodium hydrogencarbonate is heated it breaks down to form carbon dioxide. This is a thermal decomposition reaction. The carbon dioxide expands making the cake rise. Carbon dioxide will turn limewater cloudy Sodium hydrogencarbonate  Sodium carbonate +Water+Carbon Dioxide 2NaHCO 3  Na 2 CO 3 +H2OH2O+CO 2

C1f FOOD ADDITIVES KEY WORDS: Immiscible Emulsifier Hydrophobic hydrophilic EMULSIFIERS Oil and water do not mix. An emulsifier is a substance that is added to help oil and water mix and not separate into layers Oil droplet Emulsifier molecule Water Examples of food containing emulsifiers 1.Mayonnaise 2.Milk 3.Ice cream 4.Cosmetics – face cream, lipstick etc 5.Paint Examples of emulsifiers Egg yolk and mustard Emulsifiers have 2 parts Hydrophobic tail – is attracted to oil Hydrophilic head – is attracted to water. The oil and water are held together so they can’t separate Emulsion Oil and water mixed oil water

C1g SMELLS Properties of perfumes Evaporates easily (volatile) so that the particles reach the nose Non-toxic so that it doesn’t make the user ill Doesn’t react with water so that it doesn’t react with sweat Doesn’t irritate the skin so that it doesn’t cause harm Doesn’t dissolve in water so that it doesn’t wash off too easily ESTERS Have pleasant smells Acid + alcohol  ester + water The acid and the alcohol have to be warmed and a catalyst of concentrated sulfuric acid is added Nail varnish doesn’t dissolve in water because… the attraction between particles in nail varnish and water are weaker than the attractions between the nail varnish. A solution is a mixture of a solvent and a solute Solvent = liquid that does the dissolving Solute = solid that is dissolved Soluble = if it can dissolve in a particular solvent Insoluble = if it can’t dissolve in a particular solvent Testing on animals Advantage: Ensure the are safe to use Disadvantage: It’s expensive to look after the animals Some people believe it’s morally wrong

C1h PAINTS AND PIGMENTS KEY WORDS: Phosphorescent Thermochromic Oxidised Emulsion Colloid dispersed PHOSPHORESCENT These pigments absorb energy in the light and release it in the dark. Used for warning signs and clock faces THERMOCHROMIC These pigments change colour when heated or cooled. Used for strip thermometers and also mugs, baby spoons, kettles to warn that something is hot. PAINTS contain: Pigment – coloured substance Solvent – thins paint so it spreads easily Binding medium - sticks the pigment to the surface A colloid is a mixture in which one substance is spread or dispersed evenly in another substance. The particles in a colloid don’t separate because they are too small. Paints are colloids. When paint dries, the solvent evaporates. When oil paint dries, the oil is also oxidised by the oxygen in the air. This makes the shiny surface. They are safer than using radioactive substances which can cause cancer.