CHEMISTRY REVISION GUIDE for IGCSE Coordinated Science This revision guide is designed to help you study for the chem chemis istry try part part of the the IGCS IGCSE E Coor Coordi dina nate ted d Scie Scienc nce e cour course se..
Some very useful websites to help you further your underst understandin anding g include: include: http://www.docbrown.info/ - whilst not the prettiest site this contains a lot of very useful and nicely nicely expla explaine ined d info informa rmatio tion. n. http://www.bbc.co.uk/schools/gcsebitesize/scienc e/ - well presented with many clear diagrams, animations and quizzes. Can occasionally lack depth. http://www.chemguide.co.uk/ - whilst mostly tar targete geted d at A-Le A-Leve vels ls this this site site cont contai ains ns very very deta detail iled ed information suitable for those looking to deepen thei theirr know knowle ledg dge e and and hit hit the the high highes estt grad grades es.. •
The The guide ide contains ins everyth rythin ing g tha that the syll yllabu abus say says you need eed you need eed to know, ow, and and nothi othin ng extra tra.
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The material that is only covered in the supplementary part of the course (which can be ignored by core cand candid idat ates es)) is high highli ligh ghte ted d in dash dashed ed box boxes: es:
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Whils ilst this gui guide is intended to help elp with with your revisio sion, it should not be your only revision. It is intended as a star starti ting ng poin pointt but but onl only a starting ting poin oint . You should make sure that you also read your text books and use the internet to supplement your study in conjunction with your your sylla syllabus bus docume document. nt.
Finally, ly, remember revisi visio on is not jus just readin ading g but shoul ould be an acti active ve proc proces esss and and could ould invo involv lve: e: Making Making notes notes Cond Conden ensi sing ng clas classs note notess Drawing Drawing Mind-map Mind-mapss Prac Practi tici cing ng past past exam exam ques questi tion onss Making Making flashcar flashcards ds The golden rule is that what makes you think makes akes you learn. • • • •
Whils ilst this guid guide e does contain the the entir tire sylla yllab bus, it jus just has the bare minimum and is not in itself sufficient for those candidates aim aiming for the high ighest est gra grades. If that hat is you, you should make sure you read around a range of sour source cess to get get a deep deeper er know knowle ledg dge e and and unde underrstan standi ding ng..
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Happy studying, Mr Field.
C3: PETROCHEMICALS – Refining Crude Oil Hydrocarbons Hydrocarbons are compounds of hydrogen and carbon only. The carbons are linked together with hydrogen atoms attached to them. They carbons can be arranged in straight c hains (1), branched chains (2) or even rings (3).
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Refining Oil – Fractional Distillation Oil is a mixture of hundreds of hydrocarbons. This mixture has to be separated into its useful components using fractional distillation. Very hot crude oil is pumped into the fractionating column where the hydrocarbons separate out by their boiling points, rising through the column until they get cold enough to condense. The compounds that condense at a particular temperature are called a FRACTION. fuel gas, 1-4 carbons
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Bubble Caps: the gaseous fractions bubble up through these until they get cool enough when they then condense.
petrol, 5-9 carbons naptha, 6-11 carbons kerosene, 11-18 carbons
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diesel, 15-21 carbons fuel oil, 20-27 carbons Greases and wax, 25-30 carbons
ALKANES The simplest hydrocarbons are the alkanes, they are saturated hydrocarbons which means they only contain single bonds. They are unreactive and make good fuels and solvents.
HOTTER As you move down the column, the fractions have longer carbon chains. This increases the attractive forces molecules which leads to: Higher boiling points Higher viscosity Lower flammability Fuel Gas – used for fuel, and to make other chemicals Naptha – used mostly to make other useful compounds Kerosene – fuel for aeroplanes Fuel oil – fuel for large ships Bitumen – used to surface roads •
bitumen, 35+ carbons FORMULAS between Molecular formula: tells you all the atoms present in a molecule. Quick to write but little information.
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ALKENES These are unsaturated which means they contain at least one double bond. They are very valuable as a starting point for making lots of other compounds....more on the next page!
Graphical formula: drawing showing how all the atoms in a molecule are connected – takes longer but tells you much more information.
C13: COLLOIDS Colloids A colloid is a mixture of one very fine particles of one phase of matter evenly spread throughout another. There are three major types of colloid: Sol – fine particles of solid suspended in a liquid, for example blood (red blood cells suspended in water) or paint (pigment particles suspended in water) Gel – small droplets of liquid trapped in a solid matrix, for example strawberry jelly (water trapped in solid gelatine) Emulsion – fine droplets of one liquid suspended in another, for example mayonnaise (oil droplets suspended in vinegar) or milk (fat droplets suspended in water)
Emulsifiers An emulsifier is a substance used to help make an emulsion by allowing the two liquids to mix without dissolving. For example you can’t make mayonnaise without egg yolk, the lecithin in the egg yolk is an emulsifier and allows the particles of oil to stay suspended in the vinegar. W ithout egg yolk the oil and vinegar would separate out straight away. Emulsifiers work in a similar way to detergents. They are large molecules with one end able to dissolve in one type of substance and the other end able to dissolve in another type. So for example, in an oil/water emulsion, one end of the emulsifier can dissolve in water and the other in oil allowing small droplets of oil to be suspended in the water (or vice versa).
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Diagram shows droplets of oi ue suspen e in water (red)
This box is blank because there’s just not that much in this unit!
Colloids and Light Colloids are always opaque (not transparent), light can’t travel through them. The reason for this is that as photons of light hit the suspended particles they bounce off in a random direction rather than passing straight through, this is called scattering. You can see this effect when you bend a plastic ruler too much. Normally light passes straight through it but when you bend it just enough, you cause small areas of plastic molecules to rearrange themselves whilst others stay as they were. When light hits these areas it bounces off rather than passing straight through so the ruler appears white rather than transparent. Longer (redder) wavelengths of light get scatt ered less than shorter (bluer) ones. This is what causes the colours of a sunset – the bluer colours of sunlight get scattered by dust suspended in the air whereas the redder colours are able to pass straight through.