Core Chemistry (C1)

1. Core Chemistry (C1) • Topics: • Emulsifiers • Cooking and Chemical Change • Perfumes • Kinetic Theory • Solutions • Paints and Special Pigments • Polymers • Hydrocarbons; Alkanes and Alkenes • Fractional Distillation • Cracking and Hydrocarbon properties and bonds • Burning fuels

2. Emulsifier Additives make food last longer • Food colours – make the food look more appetising • Flavour enhancers – bring out the taste and smell of food without adding a flavour of their own • Antioxidants – help to preserve food Emulsifiers help oil and water mix(emulsion) When you add some emulsifier to oil and water, the oil forms droplets surrounded by a coating of the emulsifier with the hydrophilic part facing outwards. Other oil droplets get repelled by the hydrophilic part of the emulsifier whilst any water molecules latch on so the emulsion doesn’t separate out. Hydrophilic (likes water, hates oil) Hydrophobic (likes oil, hates water) Key Words: Solution: a mixture of its solute and solvent that does not separate out Solute: the substance being dissolved Solvent: the liquid it’s dissolving in Soluble: it will dissolve Insoluble: it won’t dissolve Solubility: a measure of how much will dissolve

3. Cooking and Chemical Change Some foods need to be cooked e.g. boiling, grilling, frying etc… • Better taste/texture • Easier to digest • Harmful microbes are killed (from high temperatures) • Some foods such as kidney beans contain poison when raw Cooking can cause chemical changes; e.g. Eggs and meat – good sources of protein, protein molecules change shape when heated. The energy from cooking breaks some of the chemical bonds in the protein allowing the molecule to take a different shape. The food also gets a more edible texture. This change is irreversible and is called denaturing. e.g. Potatoes – potatoes are plants meaning each potato is surrounded by a rigid cell wall made of cellulose. Humans cannot digest cellulose. Cooking the potato ruptures the cell walls. It makes the starch grains inside the cell swell up and spread out. These changes make the potato softer and more flexible and also much easier to digest. 2NAHCO₃ Na₂CO₃ + CO₂ + H₂O

4. Perfumes Esters are made by etherification: Acid + Alcohol = Ester + Water Perfumes need certain properties… Easily Evaporates – So the perfume particles can reach the nose Non- Toxic – so it doesn’t poison you Doesn’t react with water – so it doesn’t react with the water in your sweat Doesn’t irritate the skin – so you don’t get a rash/burn Insoluble in water – so it doesn’t wash off every time you get wet to make an ester… Mix 10cm³ of a carboxylic acid e.g. ethanoic acid with 10cm³ of an alcohol such as ethanol. Add 1cm³ of concentrated sulphuric acid to this mixture, warm gently for about 5 minutes. Add the mixture to 150cm³ of sodium carbonate solution(to neutralise the acids) and smell carefully. A fruity smell should be the result.

5. Kinetic Theory – Forces between Particles Solids: strong forces of attraction between the particles. If you heat the solid and give the particles more energy eventually it will melt and become a liquid Liquids: some forces of attraction between the particles. If you heat the liquid eventually it will boil and become a gas Gases: no forces of attraction between the particles. The hotter the gas gets the faster they move, it expands when heated or the pressure increases. Volatity… Perfumes need to be quite volatile so they can evaporate enough to be smelt. The particles in the perfume have very weak forces of attraction between them meaning its easy for the particles to overcome this force and escape. You only need a little heat energy (body temperature) to make the perfume evaporate.

6. Solutions Nail varnish is insoluble in water.. The molecules of nail varnish are strongly attracted to each other. The attraction is stronger than the attraction between the nail varnish molecules and the water molecules The molecules of water are strongly attracted to each other. This attraction is stronger than the attraction between the water molecules and the nail varnish molecules. Nail varnish is soluble in acetone(nail varnish remover) … The attraction between the acetone molecules and the nail varnish molecules is stronger than the attractions holding the two substances together.

7. Paints and Pigments Pigments – give paints their colour Binding medium – liquid that carries the pigment parts and holds them together Solvent – thins the paint to make it easier to spread Colloids • A colloid consists of really tiny particles of one kind of substance mixed into another substance. • The particles can be bits of solids, droplets of liquids or bubbles of gas. • Colloids don’t separate out because the particles are so small they don’t settle at the bottom. • A paint is a colloid where particles of the pigment (usually a solid) are dispersed through a liquid. Oil paint dries in two different stages: • The solvent evaporates 2) The oil is oxidised by oxygen in the air before it turns to a solid Thermochromic Pigments– change colour when heated Phosphorescent Pigments – glow in the dark

8. Polymers • Plastics are long chain molecules called polymers • They need pressure and a catalyst to be made • The forces between the molecules determine the properties of the plastic; - Weak Forces: if the plastic is made up of long chains that are held together by weak intermolecular forces then the chains will be free to slide over each other. This means that plastic can be stretched easily and will have a low boiling point -Strong Forces: some plastics have stronger between the polymer chains , these might be covalent bonds between the chains or cross-linking bridges. These plastics higher melting points are rigid and can’t be stretched as the crosslink's hold the chains firmly together.

9. Hydrocarbons; Alkanes, Alkenes Alkanes all have C-C single bonds • CnH₂n+₂ alkane formula • Won’t form polymers (no double bonds to open up) • Methane, Ethane, Propane, Butane Alkenes all have C=C double bonds • CnH₂n alkene formula • Can form polymers (double bonds can open up and join onto things) • Ethene, Propene, Butene You can do a test with bromine water: Alkane: saturated compound, no reaction it will stay bright orange. Alkene: an addition reaction takes place, bromine will add to the double bond, the bromine water is decolourised.

10. Fractional Distillation of Crude Oil • Crude oil is a mixture of lots of different hydrocarbons ( chains of different carbon atoms) • The different compounds are separated by fractional distillation. The oil is heated until most of it has turned into gas. The gases enter the fractional distillation column and the bitumen(liquid bit) is drained out at the bottom. • It is hottest at the bottom and gets cooler as you go up. • The longer hydrocarbons have higher boiling points – they turn back into liquids and drain out of the column early on. • The shorter hydrocarbons have lower boiling points – they turn to liquid and drain out of the column much later on. • You end up with the crude oil mixture separated out into different fractions.

11. Cracking and Hydrocarbon Properties and Bonds Hydrocarbon properties change as the chain gets longer… • Size of the boiling point increases • It gets less flammable • More viscous (doesn’t flow as easily) • Less volatile (doesn’t evaporate as easily) There are two important types of bond in crude oil: • The strong covalent bonds between the carbons and hydrogens within each hydrocarbon molecule • The intermolecular forces of attraction between different hydrocarbon molecules in the mixture When the crude oil is heated the molecules are supplied with extra energy. This causes the molecules to move about more. Eventually a molecule might have enough energy to overcome the intermolecular forces that keep it with the other molecules. It then goes off as a gas. The covalent bonds holding each molecule together are much stronger than the intermolecular forces so they don’t break. This is why you don’t end up with lots of small molecules. The intermolecular forces of attraction break a lot more easily in small molecules than they do in big molecules. This is because they are much stronger between big molecules than they are between small molecules. That’s why big molecules have higher boiling points than smaller molecules do. CRACKING: Splitting up long chain hydrocarbons. It turns long alkane molecules into smaller alkane and alkene molecules which are more useful. HOT + A CATYLAST

12. Burning Fuels COMPLETE COMBUSTION HAPPENS WHEN THERE IS PLENTY OF OXYGEN Hydrocarbon + oxygen carbon dioxide + water (+energy) e.g. CH₄+2O₂ 2H₂O + CO₂ (+energy) [make sure it’s balanced] INCOMPLETE COMBUSTION HAPPENS WHEN THERE ISN’T ENOUGH OXYGEN Hydrocarbon + oxygen carbon dioxide + water + carbon monoxide + carbon (+energy) e.g. 4CH₄+2O₂ C + 2CO + CO₂ + 8H₂O (+energy) [make sure it’s balanced]