Organic Chemistry - Alkanes and Alkenes

Question 1

What does saturated mean?

Answer 1

There are no double or triple bonds.

• Alkanes are saturated.

Question 2

What does unsaturated mean?

Answer 2

Contains a double/triple/etc bond.

• Alkenes are unsaturated.

Question 3

What is general formula for Alkanes?

Answer 3

C_nH_2n+2

Question 4

What is the general formula for Alkenes?

Answer 4

C_nH_2n

Question 5

What are isomers?

Answer 5

Molecules with the same molecular formula, but different structural formulae.

Question 6

What happens when methane reacts with bromine in the presence of UV light?

Answer 6

bromomethane is formed

Question 7

What does homologous series mean?

Answer 7

A homologous series is “family” of organic compounds which:

• contain the same functional group therefore similar chemical properties
• differ from one another by CH₂
• because they get larger they have a trend in physical properties (like the fractions in crude oil)

Question 8

How to test for an Alkenes?

Answer 8

Add ethene to bromine water, shake it, and it will become colourless. Addition reaction.

Question 9

How can polymers be made?

Answer 9

• addition polymerisation
• condensation polymerisation

Question 10

What is addition polymerisation?

Answer 10

The joining together or many small molecules called monomers.

Question 11

What is condensation polymerisation?

Answer 11

• Two different monomers are added to create a polymer, which also produces a small molecule, which is normally water, but sometimes HCl.

Question 12

What’s an example of condensation polymerisation?

Answer 12

• The making of nylon.

Question 13

How can ethanol be produced?

Answer 13

• fermentation
• production from ethene

Question 14

Uses of polypropene

Answer 14

• ropes
• crates

Question 15

Uses of polyethene

Answer 15

• plastic bags
• plastic bottles

Question 16

Uses of polychloroethene

Answer 16

• drainpipes
• replacement windows

Question 17

What are the problems associated with disposing of polymers?

Answer 17

• Polymers or plastics cannot be broken down due to their many strong covalent bonds they are inert (unreactive).
• The methods of disposal are landfill or incineration.

Question 18

What does biodegradable mean?

Answer 18

Something which can decompose in the ground and is broken down by living organisms/bacteria.

Question 19

What happens during the hydration of ethene?

Answer 19

• Ethene and steam are passed over phosphoric acid (acts as a catalyst) to create ethanol.
• Temperature is about 300ºC.
• Pressure is at about 60-70 atmospheres.
• C₂H₄ + H₂O → C₂H₅OH.

Question 20

What happens during the manufacture of ethanol using fermentation?

Answer 20

• A sugar (e.g. glucose) in converted into ethanol using yeast.
• The temperature is about 30ºC.
• The pressure is normal.

Question 21

What are the advantages of producing ethanol by hydration?

Answer 21

• Quite chea__p because ethene (which comes from crude oil) is not very expensive and not much is wasted.
• The rate of reaction is very fast.
• The product made is of a very high quality (pure).
• Low labour costs.

Question 22

What are the disadvantages of producing ethanol using hydration?

Answer 22

• Ethene comes from crude oil, which is a finite resource and therefore will run out.
• The process is done at a high temperature and high pressure and it is a continuous process, so the equipment needed is expensive.

Question 23

What are the advantages of fermentation to produce ethanol?

Answer 23

• Sugar and yeast are both renewable resources.
• Equipment needed is quite basic and quite cheap.

Question 24

What are the disadvantages of fermentation to produce ethanol?

Answer 24

• The ethanol is impure (and not very concentrated) and needs to be distilled and purified.
• The rate of reaction is very slow.
• It is done as a batch process and therefore labour costs are quite expensive.

Question 25

What happens during the dehydration of ethanol?

Answer 25

• The water is removed from ethanol to produce ethene in a dehydration reaction.
• Ethanol vapour is passed over a hot catalyst of aluminium oxide (Al₂O₃) which provides a large surface area for the reaction.
• C₂H₅OH → C₂H₄ + H₂O

Question 26

What is made during the complete combusion of alkanes?

Answer 26

Complete combusion occurs when there is plenty of oxygen to burn with the alkane.

• alkane + oxygen → carbon dioxide + water (+ energy)
• CH₄ + 2O₂ → CO₂ + 2H₂O

Question 27

What is made during the incomplete combustion of alkanes?

Answer 27

Incomplete combustion occurs when there is not enough oxygen to burn with the alkane.

• alkane + oxygen → carbon + carbon monoxide + carbon dioxide + water (+ energy)
• the symbol equation depends on how much oxygen is present

Question 28

What would the repeat unit for poly(ethene) look like?

Answer 28

Question 29

What would the repeat unit for poly(propene) look like?

Answer 29

Question 30

What would the repeat unit for poly(chloroethene) look like?

Answer 30

Question 31

Complete the chemical equation for the reaction between ethene and bromine water

C₂H₄ + Br₂ →

Answer 31

C₂H₄Br₂

Question 32

Why is the second method a safer way to measure the boiling points of organic compounds?

Answer 32

Organic compounds are flammable, so the second method reduces the risk of fire.

Question 33

What is a raw material which can be used as a source of C₆H₁₂O₆?

Answer 33

Cane sugar / sugar beet.