Organic Chemistry - Crude Oil, Alkanes and Alkenes

Question 1

What is meant by the term: homologous series?

Answer 1

A group of substances with:
-The same general formula
-Similar chemical properties because they have the same functional group
-A trend in physical properties

Question 2

What is a functional group:

Answer 2

An atom or group of atoms that determine the chemical properties of a compound

Question 3

What are isomers:

Answer 3

Molecules with the same molecular formula but with a different displayed formula.

Question 4

How can you classify a substitution reaction of organic compounds?

Answer 4

In a substitution reaction an atom or group of atoms is replaced by a different atom or group of atoms.

Question 5

How can you classify an addition reaction of organic compounds?

Answer 5

An addition reaction occurs when an atom or group of atoms is added to a molecule without taking anything away.

Question 6

How can you classify a combustion reaction of organic compounds?

Answer 6

A combustion reaction is a reaction with oxygen. Combustion of hydrocarbons with excess oxygen gives the products water and carbon dioxide, and also releases heat energy (exothermic reaction).

Question 7

What are refinery gases (LPG) used for?

Answer 7

Domestic heating and cooking.

Question 8

What is petrol used for?

Answer 8

Fuel for cars (gasoline)

Question 9

What is kerosene used for?

Answer 9

Fuel for aircrafts.

Question 10

What is diesel used for?

Answer 10

Diesel engines (fuel for trains)

Question 11

What is heavy fuel oil used for?

Answer 11

Ships and power stations.

Question 12

What is bitumen used for?

Answer 12

Surfacing roads.

Question 13

What are the possible products of complete and incomplete combustion of hydrocarbons with oxygen in the air?

Answer 13

Complete combustion happens where there is enough oxygen, producing carbon dioxide and water.

Incomplete combustion happens when there is not enough oxygen, with possible products being carbon monoxide, carbon, carbon dioxide and water.

Question 14

What happens in car engines when the temperature is high enough?

Answer 14

Nitrogen and oxygen from the air react, forming oxides of nitrogen.

Question 15

Explain how the combustion of some impurities in hydrocarbon fuels results in the formation of sulfur dioxide:

Answer 15

Fossil fuels such as coal, gas and oil are derived from crude oil. These fuels are hydrocarbons, but also include impurities such as sulfur. When the fuels are burned, sulfur dioxide is produced which can escape into the atmosphere.

Question 16

How does sulfur dioxide and oxides of nitrogen contribute to acid rain?

Answer 16

If sulfur dioxide reacts with water and oxygen then sulfuric acid is formed. If it reacts with just water, then a weaker acid called sulfurous acid is formed.

In car engines the temperature is high enough for the nitrogen in the air to react with oxygen to produce oxides of nitrogen, in the atmosphere these nitrogen oxides can produce nitric acid.

Question 17

Describe how long chain alkanes are converted to alkenes and shorter-chain alkanes by catalytic cracking:

Answer 17

Cracking involves the thermal decomposition of long-chain alkanes into shorter-chain alkanes and alkenes.

Question 18

What catalysts can be used in cracking longer chain alkanes?

Answer 18

Silica or alumina

Question 19

What temperature is required in catalytic cracking?

Answer 19

600C

Question 20

Explain why cracking is necessary, in terms of the balance between supply and demand for different fractions:

Answer 20

Cracking converts long chain hydrocarbons into short chain hydrocarbons.

Long-chain alkanes are broken down into alkanes and alkenes of shorter length.

Crude oil contains a surplus long chains.

Shorter chain hydrocarbons are in greater demand, e.g. petrol.

Cracking also produces alkenes which are used in making polymers and ethanol.

Question 21

Describe the reactions of alkanes with halogens in the presence of ultraviolet radiation, limited to mono-substitution:

Answer 21

Alkanes react with halogens in the presence of UV light, e.g. sunlight.

A hydrogen atom in the alkane is replaced by a halogen atom.

Question 22

What is the difference between alkenes and alkanes reacting with halogens?

Answer 22

Alkenes will react with halogens without UV light, as they are more reactive than alkanes.

Question 23

Alkenes + Bromine ->

Answer 23

Alkenes + Bromine -> Dibromoalkanes

Question 24

Describe the reaction between ethene and bromine:

Answer 24

Ethene reacts with bromine to produce dibromoethane. The double bond between the two carbon atoms breaks and the bond between the bromine atoms in the bromine molecule breaks. The two bromine atoms separate and the carbon atoms in the alkene are able to form single covalent bonds, with each bromine atom producing the new compound dibromoethane.

Question 25

What kind of reaction is an alkene + bromine reaction known as?

Answer 25

An addition reaction, because the 2 bromine atoms are added into the original structure of the alkene to produce one single product.

Question 26

How can you distinguish between an alkane and an alkane?

Answer 26

We use bromine water. When bromine water is added to an alkane, no colour change is seen. Bromine can not be added into the alkane structure so remains in the solution. The solution will stay orange as bromine will still be present.

When bromine water is added to an alkene, the bromine is added into the structure. Therefore, the bromine is removed from the solution and the orange colour disappears. When bromine water is added to an alkene, a colour change from orange to colourless is observed.