Organic Chemistry

Question 1

Describe the production and extraction of crude oil and natural gas

Answer 1

Crude oil is a fossil fuel formed over millions of years from the remains of sea creatures such as plankton which died are became buried in mud on the seabed. Sediment built up and the high pressure and temperature turned the dead plankton into oil and gas which was trapped under the layers of rock.
It is extracted by drilling through the rock using an oil rig.

Question 2

What is a biomass?

Answer 2

A resource made from living organisms.

Question 3

What is a hydrocarbon

Answer 3

A compound which contains hydrogen and Carbon

Question 4

What is meant by the term homologous series, give two examples

Answer 4

A family of compounds with the same general formula and similar properties
examples are
Alkanes CnH2n+2
Alkenes Cn H2n

Question 5

What does the term saturated mean in the context of organic chemistry

Answer 5

A molecule which contains only single bonds, it has no double covalent bonds
eg the alkanes

Question 6

What is a displayed formula?

Answer 6

It is where all of the atoms are shown with their bonds eg ethane

              H      H
               |        |
     H  _   C _  C _ H
                |       |
               H      H

Question 7

What are the names of the first 6 alkanes in order of carbon atoms

Answer 7

1. methane
2 ethane
3 propane
4 butane
5 pentane
6 hexane

Question 8

What is fractional distillation?

Answer 8

The method used to separate miscible liquids with different boiling points

Question 9

What is meant by a fraction in organic chemistry

Answer 9

A mixture of molecules with similar boiling points

Question 10

Describe how fractional distillation is used to separate different hydrocarbons from crude oil.

Answer 10

1. The oil is heated and vapourised before it passes into the fractioning tower.
2. The fractioning tower is hotter at the bottom than it is at the top.
3. The hydrocarbons cool as they rise up the tower and condense at different heights due to their different boiling points. The lower boiling points condense higher up.
4. The hydrocarbons with large molecules are collected at the bottom of the tower as liquids.
5. Those with smaller molecules condense and are collected nearer the top.
6. The very top of the tower collects liquid petroleum gas (LPG)

Question 11

Identify the different hydrocarbons produced during the fractional distillation of crude oil and give their uses. Work in order to top to bottom.

Answer 11

1. LPG - heating fuel for homes and business not on mains supply and fuel for some cars
2. Petrol - for vehicles
3. Naptha - used for making chemicals
4. Kerosene - Aeroplane fuel jet engines
5. Diesel - vehicles including buses and lorries
6. Lubricating oil - used in engines
7. Heavy fuel oil - used for some central heating systems and ships
8. Bitumen - used for roads and on roofs.

Question 12

Equations for the complete combustion of hydrocarbons made simple

Answer 12

1. The number of molcules of carbon dioxide produced will equal the number of carbon atoms in the hydrocarbon eg methane 1 ethane 2 etc
2. The number of molecules of water will be half the number of hydrogen molecules in the hydrocarbon eg methane 2 ethane 3 etc
3. Now count the number of oxygen molecules on the products side in CO2 and H2O, the number of oxygen molecules on the reactants will half that. eg if there are 4 it will be 2O2
4. If there are an odd number of O2 molecules double the balancing numbers of the hydrocarbon CO2 and H2O so that they are even- you can’t have half an O2!

Question 13

What is meant by flammability?

Answer 13

How easily a substance catches fire. Flammability depends on the size of the molecules. The shorter the hydrocarbon the more flammable it is and it burns with a cleaner flame.

Question 14

What is meant by viscosity?

Answer 14

It is how easily a liquid flows. The lower the viscosity the more runny it is. The shorter hydrocarbons the lower the viscosity.

Question 15

Describe the process of cracking

Answer 15

Cracking is a thermal decomposition reaction which breaks down the longer alkanes into smaller ones which are more in demand. This process also produces alkenes which are unsaturated having a double covalent bond. The alkenes are used to make many other substances such as polymers and medicines.
Catalytic cracking involves heating the alkanes to vapourise them and passing them over a hot catalyst.
Steam cracking involves mixing the vapourised alkanes with steam at a very high temperature.

Question 16

Describe the structure of alkenes and how they are tested.

Answer 16

They are an homogenous series containing a double covalent bond which means they are unsaturated. Ethene is the first in the series because 2 carbon atoms are needed.
Alkenes react with bromine water breaking down the double bond and the reaction mixture goes colourless. This is the test for alkenes.

Question 17

Explain the structure of a polymer and give an example

Answer 17

Polymers are long chain molecules where smaller molecules called monomers are joined together.
An example polythene (polyethene) PVC is another