7.2 Reactions of alkenes and alcohols (Triple)

Question 1

What bond do alkenes have?

Answer 1

At least one double covalent bond

Question 2

What is the general formula of alkenes

Answer 2

C_nH_2n

Question 3

What are alkenes?

Answer 3

An unsaturated hydrocarbon with the functional group C=C.

Question 4

What are the first four alkenes?

Answer 4

• Ethene (C₂H₄)
• Propene (C₃H₆)
• Butene (C₄H₈)
• Pentene (C₅H₁₀)

Question 5

Why are alkenes described as unsaturated?

Answer 5

Alkenes contain two fewer hydrogen atoms than the alkane with the same amount of carbons.

Question 6

What happens to molecules with the same functional group?

Answer 6

They react in similar ways

Question 7

What are the addition reactions with alkenes? (4)

Answer 7

• (Incomplete) combustion (w/ oxygen)
• Hydrogenation (w/ hydrogen)
• Hydration (w/ water)
• Reaction with halogens

Question 8

What do alkenes produce when reacting with oxygen in combustion? (3) Why?

Answer 8

• Water and carbon dioxide (like other hydrocarbons)
• Burn with a smokey flame; because they produce burnt carbon particles due to incomplete combustion.

Question 9

What conditions are needed to react alkenes with hydrogen in hydrogenation? (2)

Answer 9

• Nickel catalyst
• ~150ºC

Question 10

What do alkenes produce when reacting with hydrogen in hydrogenation? Why?

Answer 10

Alkanes; because the addition of hydrogen atoms across the carbon-carbon double bond causes the double bond to convert into a carbon-carbon single bond.

Question 11

How do alkenes react with hydrogen, water and halogens?

Answer 11

By the addition of hydrogen atoms which causes the carbon-carbon double bond to convert into a carbon-carbon single bond.

Question 12

What conditions are needed to react alkenes (ethene) with water in hydration? (4)

Answer 12

• Steam
• ~300ºC
• 70 atm
• Catalyst (e.g. phosphoric acid)

Question 13

What type of reaction is the hydration reaction of alkenes and water?

Answer 13

Reversible

Question 14

What is an advantage of making ethanol by hydrating ethene?

Answer 14

Produces a high yield of ethanol: can be increased by passing back any unreacted ethene and steam through the catalyst.

Question 15

What do the first four alkenes produce when reacting with chlorine? (4)

Answer 15

• Dichloroethane
• Dichloropropane
• Dichlorobutane
• Dichloropentane

Question 16

What do the first four alkenes produce when reacting with bromine? (4)

Answer 16

• Dibromoethane
• Dibromopropane
• Dibromobutane
• Dibromopentane

Question 17

What do the first four alkenes produce when reacting with iodine? (4)

Answer 17

• Diiodoethane
• Diiodopropane
• Diiodobutane
• Diiodopentane

Question 18

What are the main uses of alcohol? (3)

Answer 18

• Fuels
• Solvents
• Alcoholic drinks

Question 19

What is the functional group for alcohols?

Answer 19

-OH

Question 20

What are the first four alcohols?

Answer 20

• Methanol (CH₃OH)
• Ethanol (C₂H₅OH)
• Propanol (C₃H₇OH)
• Butanol (C₄H₉OH)

Question 21

What are the disadvantages of making ethanol by hydrating ethene?

Answer 21

• The reaction requires a lot of energy due to high temperatures
• The ethene comes from crude oil and is non-renewable.

Question 22

What are ways to make ethanol? (2)

Answer 22

• Hydration of ethene
• Fermentation of sugar

Question 23

Describe the process of fermentation to produce ethanol. (2)

Answer 23

1) Sugar solution (e.g. glucose) mixed with yeast.
2) Yeast converts sugar solution into solution of ethanol and produces carbon dioxide.

Question 24

What conditions are needed to ferment sugar (e.g. glucose) to produce ethanol? (2)

Answer 24

• ~30ºC
• Anaerobic conditions

Question 25

What are the advantages of producing ethanol using fermentation?

Answer 25

• Low temperature means lower amount of energy required.
• Sugar used from plants so is renewable.

Question 26

What is the disadvantage of producing ethanol using fermentation?

Answer 26

Energy needed to purify ethanol by distillation as it is an aqueous solution.

Question 27

What occurs when alcohol is added to water?

Answer 27

Alcohols are soluble in water and produce a neutral solution.

Question 28

Describe the trends in solubility of alcohols in water.

Answer 28

As the number of carbon atoms increases, the solubility decreases.

Question 29

What occurs when alcohol is reacts with sodium? (2)

Answer 29

• Effervescence
• Produces hydrogen and:
  (a) sodium methoxide
  (b) sodium ethoxide
  (c) sodium propoxide
  (d) sodium butoxide

Question 30

What occurs when alcohol is reacts with oxidising agents? (1)

Answer 30

Produce carboxylic acid (e.g. methanol acid) and water.

Question 31

What occurs when alcohol is reacts with oxygen (combusted)? (1)

Answer 31

Produces carbon dioxide and water

Question 32

What are the first four carboxylic acids?

Answer 32

• Methanoic acid (HCOOH)
• Ethanoic acid (CH₃COOH)
• Propananoic acid (C₂H₅COOH)
• Butananoic acid (C₃H₇COOH)

Question 33

What occurs when carboxylic acid is dissolved in water? (2)

Answer 33

• They become weak acids
• They ionise to produce an ester and H⁺

Question 34

Explain why carboxylic acids are weak acids in terms of ionisation and pH?

Answer 34

Carboxylic acids are considered weak acids as:

• They only partially ionise [they contain less hydrogen ions than strong solution of the same concentration]
• They have a higher pH than a strong acid of the same concentration.

Question 35

What occurs when carboxylic acid is reacts with metal carbonate? (1)

Answer 35

• Produce and ester (e.g. ethyl ethanoate), carbon dioxide and water

Question 36

What occurs when carboxylic acid is reacts with an alcohol? (1)

Answer 36

• Produce ester (e.g. ethyl ethanoate) and water

Question 37

Why are esters useful?

Answer 37

• They often have a pleasant smell so are used in foods.

Question 38

What conditions are needed to react carboxylic acids with alcohol? (2)

Answer 38

• Catalyst (e.g. sulphuric acid)