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A Level Organic Chemistry > Section 3 Alkenes and Alcohols > Flashcards

Section 3 Alkenes and Alcohols Flashcards

1
Q

What are alkenes?

A

Unsaturated hydrocarbons

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2
Q

What is the generla formula for an alkene?

A

CnH2n

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3
Q

Why are alkenes reactive?

A

They have a high electron density around the double bond.

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4
Q

What type of reaction happens to alkenes?

A

Electrophilic addition

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5
Q

What are electrophiles?

A

Electron-pair acceptors

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6
Q

What is a test for unsaturation?

A

Bromine water - goes from orange to colourless in the presence of an alkene.

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7
Q

What mechanism is the bromine water test?

A

Electrophilic addition

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8
Q

Why does a polar bond form on the Br2 molecule?

A

As the bromine approaches the double bond, the electrons on it are repelled slighty, causing the delta charge.

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9
Q

Why are carbocations with more alkyl groups, more stable?

A

The alkyl groups feed electrons towards the positive charge.

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10
Q

Which carbocation is most likely to form in a reaction?

A

The most stable one.

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11
Q

What are the conditions for an electrophilic addition reaction between alkenes and sulfuric acid?

A
  • cold, conc sulfuric acid
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12
Q

What are the conditions to hydrolise an alkyl hydrogen sulfate into an alcohol?

A
  • cold water
  • warm
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13
Q

What are polymers?

A

Long chain molecules formed when lots of small molecules (monomers) join together.

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14
Q

How are addition polymers formed from alkenes?

A

The double bond of the alkenes are opened up and join to make long chains.

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15
Q

How reactive are polymers and why?

A

Unreactive - the main carbon chain of a polymer is non-polar.

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16
Q

What are the IMFs between polymers?

A

Van der Waals

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17
Q

What determines the strength of IMFs between polymers?

A

The longer the chains, and the closer together they are, the stronger the VdWs.

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18
Q

What are the opposing qualities of long, straight chain and short, branched chain polymers?

A

Long, straight chain - strong, rigid.

Short, branched chain - weak, flexible.

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19
Q

How can you make a polymer more flexible?

A

Add a plasticiser.

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20
Q

How do plasticisers work?

A

They get between the polymer chains and push them apart, reducing the strength of the IMFs.

The polymers can then slide around more and bend easier.

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21
Q

What is the IUPAC name for PVC?

A

polychloroethene

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22
Q

What are the properties of PVC?

A

Long, closely packed chains so hard but brittle at room temperature

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23
Q

What is rigid PVC used for?

A
  • drainpipes
  • windowframes
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24
Q

What is plasticised PVC used for?

A
  • electrical cable insulation
  • flooring tiles
  • clothing
25
Q

What is the IUPAC name for Teflon?

A

Polytetrafluoroethene

26
Q

How can you form alkenes from alcohols?

A

Dehydration

27
Q

What type of reaction is the dehydration of alcohol?

A

Elimination (of water)

28
Q

How is dehydration of alcohols better for the environment?

A

Alcohol is a renewable resource - ethanol can be produced by fermentation of glucose, which can be retrieved from plants

29
Q

What are the conditions for the elimination of water from alcohol?

A
  • heat
  • conc sulfuric or phosphoric acid
30
Q

What is distillation used for?

A

To separate chemicals

31
Q

Why must you distil the mixture at the end of an elimination reaction?

A

It will contain the product, reactant, acid and water.

32
Q

How can alcohols be produced from alkenes?

A

Hydration

33
Q

What type of reaction is the hydration of alkenes?

A

Electrophilic addition

34
Q

What are conditions for electrophilic addition of water to alkenes?

A
  • steam
  • high pressure and temperature
  • acid catalyst (phosphoric acid)
35
Q

How can ethanol be produced industrially?

A

Fermentation

36
Q

What is the equation and conditions for the fermentation of glucose?

A

C6H12O6(aq) —> 2C2H5OH(aq) + 2CO2(g)

  • yeast
  • 30-40oc
37
Q

Why is yeast used in fermentation?

A

It produces an enzyme.

38
Q

Why does the temperature have to be 30-40oc for fermentation?

A

That is the optimum temperature for the enzyme.

39
Q

Give some positives and negatives of fermentation?

A

+ low tech

+ cheap equipment

+ renewable resources

  • purification takes time and money
40
Q

What is biofuel?

A

Fuel made from biological material that’s recently died

41
Q

Gives some advantages and disadvantages of biofuel:

A

+ renewable

+ the carbon dioxide produced is absorbed by plants

  • petrol car engines would have to be modified
  • crops should be prioritised as food over fuel
42
Q

Give 3 equation to show that bioethanol production is carbon neutral:

A

Photosynthesis:

6CO2 + 6H2O —> C6H12O6 + 6O2

Fermentation:

C6H12O6 —> 2C2H5OH + 2CO2

Combustion of Ethanol:

2C2H5OH + 6O2 —> 4CO2 + 6H2O

6 moles of carbon dioxide in and out.

43
Q

Why is it debatable whether bioethanol production is actually carbon neutral?

A

Fossil fuels will need to be burned to power fertilising, harvesting, refining and transporting machinery.

44
Q

What is the oxidising agent used to oxidise alcohols?

A

Acidifed potassium dichromate

45
Q

What are primary alcohols oxidised to?

A

Aldehydes then carboxylic acids

46
Q

What are tertiary alcohols oxidised to?

A

They aren’t

47
Q

What are secondary alcohols oxidised into?

A

Ketones

48
Q

What are the conditions for the oxidation of primary alcohols to aldehydes?

A

Distillation

49
Q

What are the conditions for the oxidation of primary alcohols to carboxylic acids?

A

Reflux

50
Q

What are the conditions for the oxidation of secondary alcohols to ketones?

A

Reflux

51
Q

What will you observe if you add Fehling’s solution to an aldehyde?

A

Blue solution to red precipitate

52
Q

What will you observe if you add Fehling’s solution to an ketone?

A

Nothing - blue solution

53
Q

What happens when Fehling’s solution goes from blue to red?

A

The Cu2+ complex is reduced to brick-red Cu2O.

54
Q

What will you observe if you add Tollen’s reagent to an aldehyde?

A

It will go from a colourless solution to a silver mirror.

55
Q

What will you observe if you add Tollen’s reagent to a ketone?

A

Nothing - colourless solution

56
Q

What happens when Tollen’s reagent goes from colourless to silver?

A

The [Ag(NH3)2]+ is reduced

57
Q

What do you observe when potassium dichromate oxidises a substance?

A

Orange to green

58
Q

What happens to potassium dichromate when it oxidises a substance?

A

The dichromate ion, Cr2O72-, is reduced to the chronium ion, Cr3+.

59
Q

What is a way to oxidise a tertiary alcohol?

A

Burn it

A Level Organic Chemistry (9 decks)

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