Chemistry GCSE OCR - C1 Carbon Chemistry

(N.B. Things highlighted in green are the number of atoms like H2O. Things highlighted in red are 2 lots of the atom. This is used when balancing equations)

Atoms make up everything in the universe. These can join up with other atoms to create molecules. Molecules with different types of atoms in (such as Carbon Dioxide CO2) are called compounds.

Atoms have a positive charged nucleus and orbiting electrons with a negative charge. They move around the nucleus in layers called shells.

Atoms form bonds to make molecules/compounds and the electrons are involved in making these bonds. The atom may lose or gain one or more electrons and this gives a charge (positive if it loses, negative if it gains)

Charged atoms are ions. A positive will meet a negative and join together, making a ionic bond.

In a covalent bond, both the atoms share a pair of electrons.

This is how many atoms there are in a substance. In this example, Methane.

CH4 - This is the molecular formula. It shows the number and type of atoms in a molecule.

You may see an image of what the atom looks like. This is a displayed formula.

The lines are the covalent bonds and the letters are atoms. (CH4)2 If it has brackets in, it means there are however many outside the brackets, lots. In this case 2 lots of CH4.

Equations are the changes in chemicals, so when reactants turn into products. You are normally told in an exam what happens. E.g. Methane burns in oxygen, giving you carbon dioxide and water. All you do is write the equation- what happened!

methane + oxygen → carbon dioxide + water

Chemical equations can be shown in shorthand compared to word equations.

CH4 + O2 → CO2 +H2O

You will need to balance equations - Do them one atom at a time

Find an element that doesn't balance and pencil in a number - try 2 as it may work first time. It may create another imbalance so sort that one out. Eventually you will get it so don't panic

Emulsifiers are additives which make oils and water mix together.

Additives will; make food look appetising with colouring, bring out flavours with enhancers, preserve food, help oil and water blend together like in ice cream.

You can mix water and oil to make an emulsion. They are made up with droplets of one liquid, suspended in another (like when oil floats on top of water). Emulsifiers will stop the two liquids from seperating. Emulsifiers are molecules with one part that is attracted to oil and the other part attracted to water, letting them 'mix'. The part in the water is hydrophilic, the part in the oil is hydrophobic (or lipophilic).

When you cook food the chemical structure of the substance changes and they are irreversible (they won't go back). There are lots of reasons why you should cook food...

• Better taste, texture or smell.
• Some foods are easier to digest than when they are raw
• The high temperatures can kill off microbes that cause disease (like salmonella)
• Some foods are poisonous when edible like kidney beans.

When you cook proteins, the molecules change shape. The energy breaks some of the chemical bonds and allows the molecule to take a different shape. This gives it more of a solid texture (like in an egg, its whites are gooey but when it is cooked it solidifies) and its irreversible. This is called denaturing

When you cook starchy food like potato, the cells have rigid cell walls made of cellulose, stuff humans can't digest. Cooking them ruptures the cell walls. It also makes starch grains swell and spread out, which makes the potato softer.

Esters are 'responsible' for the smell of the perfumes. They can be natural or artificial. A lot of products use artificial esters because the natural ester may be near extinct.

To make an artificial ester you need a carboxylic acid (like ethanoic acid) and an alcohol (like ethanol). You heat them both together. An acidic catalyst can be used.

Acid + Alcohol → Ester + Water

These chemicals need to have other properties besides smelling nice though

• Easily evaporates - else the particles won't reach your nose
• Non-toxic - it could seep through the skin and poison you
• Doesn't react with water - it would react with sweat
• Doesn't irritate - it could aggrevate or burn the skin, you'd be out in rashes...
• Insoluble - it would end up washing off if you got wet.

This links in with the perfume bit nicely....

Companies are always developing new products to sell to us but if they pose potential health risks they need to be tested thoroughly. Some tests are carried out on animals, imagine Rover the Bulldog smelling of Impulse.....

Obviuosly, testing on animals may be deemed as being cruel by some people. It's a controversial subject.

• Some people think its better to test on animals first to check if its safe
• Others claim its cruel to cause suffering to animals to test cosmetics - especially if the tests are inconclusive (in this case - poison to the animal and humans)

Animal testing has been banned in the EU but the odd test is allowed.

SOLIDS

• Strong forces of attraction between particles. Each particle is in a fixed position and in regular latice arrangement
• The particles don't move at all, so solids keep a definite shape and volume
• The particles vibrate when heated, making them expand when heated

LIQUIDS

• There is some force of attraction between particles. They are free to move around but they sometimes to stick together
• Liquids don't keep a definite shape, but will keep the same volume
• The hotter the liquid, the more the particles vibrate - like solids

GASES

• There is no force of attraction and only interact when they collide
• They don't have a definite shape or volume and fill a container
• When heated they expand or the pressure increases