ks4 useful products from organic sources organic chemistry

© Boardworks Ltd 2003

KS4 Useful Products from

Organic Sources

ORGANIC CHEMISTRY


Crude oil

• Crude oil is a mixturemixture. It contains hundreds of different compounds. Some are small but most are large.

• Nearly all of these compounds contain carbon and hydrogen only.only.

• They are called hydrocarbons.

Hydrocarbons are molecules that contain carbon and hydrogen onlyonly.


The importance of oil

• These hydrocarbons are vital to our way of life.

• We use them as highly portable fuels for many forms of transport.

• We also use them as raw materials from which a huge range of useful everyday substances are made.


• Although we can get useful substances from oil, crude oil itself has no uses.

• In order to make crude oil into useful substances we first have to separate the mixture into molecules of similar size.

• This is done in an oil refineryoil refinery.

Making oil useful


What is crude oil?

• Crude oil is a mixture of different sized hydrocarbons. The exact composition depends upon where the oil comes from but typically it contains a lot of big molecules.

Fuel gas PetrolNaphtha KerosineDiesel Fuel Oil and bitumen

Small molecules

Medium molecules

Big molecules


Fractional Distillation

• Crude oil is split into fractions containing similar sized molecules using fractional distillationfractional distillation..

• The oil is heated until it vaporises.• It then passes up a tall tower that is

hot at the bottom but cool at the top.• As the vapour passes up this tower

the molecules cool and condense back to liquid.

cool

hot


Copy the column and arrange the fractions in the right order next to the arrows.

Fraction Boiling Range(oC)

Kerosine 150 - 240

Diesel 220 – 275

Petrol 40 - 175

Bitumen >350

Fuel gas Below 40

Lubricating oil 250-350

cool

hot

Fuel gas

Petroleum

Kerosine

Diesel

Lub. Oil

Bitumen



The boiling points of molecules

We have already said that, in general, the bigger the molecule the higher the boiling point.

0

50

100

150

200

250

300

350

0 5 10 15 20

No. Carbon atoms

B.Pt

(oC)


Here are the boiling ranges of some fractions obtained from distillation of petroleum.1. Using the previous graph, estimate the size range of the molecules present in each fraction.

Fraction Boiling Range

(oC)

Number of carbons

Fuel gas Below 40Petrol 40 - 175Kerosine 150 - 240Diesel 220 - 275

1-55-109-14

13-17


The flammability of molecules

• When hydrocarbons burn they are reacting with oxygen in the air.

• In general, the smaller the molecule the better it will mix and then react with the air.


• Flash points are (roughly) the temperature below which you cannot ignite the substance.

• Here is some flash points data for oil fractions. Link the molecule to the flash point.

Substance Flash PointKerosine <23Petrol 85 - 150Fuel Oil 23 - 61


The viscosity of molecules

• When we pour a liquid the molecules have to pass each other. The easier they do this, the runnier the liquid is.

• The molecules in fuel oil and bitumen may contain up to 400 carbon atoms in long chain structures.

• These chains easily become entangled reducing the runniness of the liquid and so those made up of big molecules tend to be viscous (treacly) not runny.


• In contrast, small molecules are more spherical and tend not to get tangled.

• They are therefore likely to have a low viscosity (be runny).

Bigger molecules

Higher viscosity

“Treacly”

Smaller molecules

Lower viscosity

“Runny”

The viscosity of molecules


Here are the viscosities of 5 hydrocarbons. The higher the value the less runny the hydrocarbon is. Draw arrows joining the hydrocarbon with the appropriate value.

Hydrocarbon Viscosity (cP)Pentane - C5H12 0.40

Hexane - C6H12 0.52

Heptane - C7H16 0.24

Octane - C8H18 0.92

Decane - C10H22 0.70


The colour of molecules

• Small hydrocarbon molecules are gases or transparent liquids.

• As the molecules get larger the colour becomes increasingly yellow through to the brown/black colour of bitumen used on roads and roof repairs.

Increasing size of molecules


The composition of fractions?

• We already know that each petroleum fraction consist of hydrocarbon molecules falling within a particular size range.

• The proportions of the different hydrocarbons present in oil can vary greatly across the world.

• It is therefore not surprising that the exact nature of the fractions collected will vary both in amount and detailed composition.

• Nonetheless most crude oil will give rise to some quantity of each type of fraction.


Using viscosity data for crude oil from different areas of the world, arrange the oils putting those with the smallest molecules first.

Crude Order Viscosity (cSt)

Saudi Arabia 47.7UK (Brent) 6.13

Norway (Gulifaks) 16.5Alaskan 31.5

Malaysian 3.431

234

5


Fuel gas

Petrol / gasoline

NaphthaParaffin / Kerosine

Diesel fuel

Fuel and lubricating oilBitumen

Burned in the refinery to fuel the distillation process, sold as LPG, purified and sold as bottled camping gas

Fuel for cars and motorcycles, also used to make chemicals.

Used to make chemicals.

Fuel for greenhouse heaters and jet engines, manufacture of chemicals.

Fuel for lorries, trains.

Fuel for the heating systems of large buildings, fuel for ships, lubricating oil.

Roofing, and road surfaces.

Uses of each fraction


Burning hydrocarbons

The apparatus below is used to test the products of combustion of a hydrocarbon.

any hydrocarbon + oxygen water + carbon dioxide

Suctionpump

Candle wax is thehydrocarbon here

ice-water

Liquid collectedcan be tested withanhydrous cobalt chloridepaper (bluepink).

Lime water


Which is a correct statement about crude oil?

A. A mixture of carbohydrates.B. Formed by the decay of dead sea

creatures.C. Consist of a mixture of very large

molecules.D. Is purified in an oil rig.


Which is a correct statement about fractionaldistillation?A. Oil is separated into fractions with the same

size molecule.B. Oil is separated into fractions with the same

density.C. Oil is separated into fractions with similar

size molecules.D. Oil is separated into alkanes and alkenes.


Which is a correct order for these fractions working down from the top of the column?

A. Fuel gas, kerosine, petrol, diesel, bitumen.B. Fuel gas, diesel, kerosine, petrol, bitumen.C. Fuel gas, petrol, diesel, kerosine, bitumen.D. Fuel gas, petrol, kerosine, diesel, bitumen.


Which of these is a true statement about the changes that occur as hydrocarbon molecules get larger?

A.Boiling point decreases.B.Viscosity increases.C.Flammability increases.D.Transparency increases.

ks4 useful products from organic sources organic chemistry

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