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Chemistry > Alcohols > Flashcards

Alcohols Flashcards

1
Q

What is the general formula for alcohols ?

A

CnH2nOH

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2
Q

What intermolecular forces do alcohols have ?

A

Dipole-dipole
Hydrogen bonding
Van der waals

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3
Q

Why do alcholds have hydrogen bonding ?

A

The slightly negative oxygen bonds with the slightly positive hydrogen.

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4
Q

What characteristics of alcohols does hydrogen bonding give ?

A

Hey can dissolve in water therefore they are good solvents.

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5
Q

What makes alcohols good solvents that can dissolve in water ?

A

Hydrogen bonding between the slightly negative oxygen and slight positive hydrogen.

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6
Q

Which is the strongest type of intermolecular bonding in alcohols.

A

Hydrogen
Dipole dipole
Van der waals

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7
Q

What is ethanol used for ?

A

Biofuel, feedstock reactant, solvents, alcoholic drinks.

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8
Q

What are the 2 main methods to produce ethanol ?

A

Fermentation

Hydration of Ethene

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9
Q

Write the equation for fermentation.

A

C6H12O6 - 2C2H5OH + 2CO2

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10
Q

What is the fermentation reaction performed by ?

A

Yeast

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11
Q

Describe the process of fermentation.

A

Yeast is a fungus that respites aerobically and produces alcohol when doing this. The yeast metabolises the glucose to make ethanol and carbon dioxide. The ethanol produced is separated from the water mixture by fractional distillation at around 78 degrees Celsius and is collected by a condenser.

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12
Q

What and why is yeast used in fermentation.

A

It is a fungus which respites anaerobically and produces yeast by metabolising the glucose to make ethanol and carbon dioxide.

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13
Q

At what temperature is ethanol separated from water in a fractionation column ?

A

78 degrees Celsius

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14
Q

What are the required conditions for fermentation ?

A

25-50 degrees Celsius
No oxygen
Ph 6-8

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15
Q

Why does temperature of fermentation have to be controlled and how is this done ?

A

Yeast is a biological life so can be killed if the term pasture is not ideal.
This is controlled in a water bath.

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16
Q

Why can no oxygen be present in fermentation ?

A

If there is no oxygen present, only water and carbon dioxide will be produced but not alcohol due to yeast respiring aerobically.
The presence of oxygen will oxidise ethanol to Ethanoic acid.

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17
Q

How can ethanoic acid be produced from ethanol ?

A

Oxidise ethanol

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18
Q

What are the advantages of fermentation ?

A

Low energy process
Uses renewable plant material
Simple equipment

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19
Q

What are the disadvantages of fermentation ?

A

Slow (few days)
Produces impure ethanol
Bath process meaning it is not constantly producing ethanol.

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20
Q

What is the catalyst for the industrial production of alcohols when there is an electrophillic addition with sulphuric acid.

A

Phosphoric acid

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21
Q

Write the equation for the hydration of ethene

A

C2H4 +H2O - CH3CH2OH

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22
Q

What is the catalyst for hydration of ethene ?

A

Phosphoric acid

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23
Q

What are the conditions for hydration of ethene to produce ethanol ?

A

High temperature - above 100 degrees Celsius

High pressure

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24
Q

What are the advantages of hydration of ethene ?

A

Highly pure alcohol
Continuous system
Fast

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25
Q

What are the disadvantages of hydration of ethene ?

A

Ethene is obtained from cracking crude oil
Expensive
Complex chemical equipment
Non-renewable fossil fuel sources.

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26
Q

Give a use of methanol ?

A

Antifreeze - liquid to stop car engines freezing.

Solvent

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27
Q

Why is methanol not used as drinking Alcohol ?

A

It would be toxic to drink and could cause blindness as well as comas

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28
Q

What is a biofuel ?

A

Fuel produced from renewable biological sources.

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29
Q

What is bioethanol ?

A

Ethanol produced by natural fermentation of carbohydrates from sugar cane or wheat crops.

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30
Q

What are the advantages of bioethanol ?

A

Renewable

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31
Q

What are the disadvantages of bioethanol ?

A

Need a lot of land to grip sugar sources which should be used for crops for LEDCs.
Need to make vehicles compatible

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32
Q

Why does bioethanol claim to be a carbon-neutral fuel ?

A

Releases same amount of carbon dioxide when burnt as was taken in by plants when they grew.

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33
Q

Write the equation to show how glucose is produced as plant photosynthesise

A

6CO2 +6H2O - C6H12O + 6O2

34
Q

Write the equation to show the carbon dioxide reased by fermentation of ethanol

A

C6H12O - 2C2H5OH +2CO2

35
Q

Write the equation for burning ethanol as a fuel.

A

2C2H5OH +6O2 -4CO2 +6H2O

36
Q

Why may bioethanol not be carbon neutral ?

A

Transportation and energy used for machinery is not considered.

37
Q

What is the ideal temperature for fermentation ?

A

25-42 degrees

38
Q

Why are alcohols not produced by nucleophilic substitution in industry ?

A

Yield is very low as rate of reaction is slow.

39
Q

What is the specific pressure used for hydration of ethene ?

A

50atm - 100atm

40
Q

What is meant by the term hydration ?

A

Reacting a substance with water or stream to add O H atoms.

41
Q

Why are tertiary alcohols hard to oxidise.

A

There is no hydrogen atoms on one of the carbons.

42
Q

What is dehydration ?

A

Removal of water

43
Q

In what conditions are alcohols dehydrated ?

A

Concentrated sulphuric acid which refluxes at 180 degrees.

44
Q

What are the products of dehydration of alcohols.

A

Alkenes

Biproduct of water

45
Q

What is the mechanism for a dehydration reaction called ?

A

Elimination

46
Q

Why are alkenes good to use for addition polymerisation ?

A

This allowed production of polymers without using crude oil. The polymers come from a renewable origin.

47
Q

How can you prevent a mixture of products when dehydrating alcohols ?

A

Use only symmetrical and primary alcohols.

48
Q

What is the suffix when naming aldehydes ?

A

al
Methanal
Ethanal

49
Q

Draw the general structure of an aldehyde.

A

In notes

50
Q

Draw the general structure of a ketone.

A

In notes

51
Q

Describe the general structure of an aldehyde.

A

Aldehydes have a CdoublebondO cabronyl group ya the end of their carbon chain.

52
Q

Describe the general structure of Ketones

A

Ketones have a CdoublebondO carbonyl group in the middle of the carbon chain.

53
Q

What is the suffix for naming ketones ?

A

One

Propan-2-one

54
Q

Describes the structure of a carboxylic acid group.

A

They have a CdoublebondO carbonyl group at the end of their carbon chain and a hydroxyl OH group.

55
Q

What are primary alcohols oxidises to and with what reagent ?

A

Aldehydes

Aqueous solution of acidified potassium dichromate VI

56
Q

Write the equation for the oxidisation of primary alcohols

A

RCH2OH+[O] - RCHO +H2O

57
Q

What happens if primary alcohols are reaves with excess oxygen ?

A

A reflux will occur meaning that the aldehyde is further oxidised intro a carboxylic acid.

58
Q

Write the general equation to show how an aldehyde is oxidised into a carboxylic acid ?

A

RCHO + [O] - RCOOH

59
Q

Complete the full equation for oxidising alcohols to carboxylic acids

A

RCH2OH+2[O] - RCOOH +H2O

60
Q

What do secondary alcohols become when they are oxidised ?

A

Ketones

61
Q

What is the reagent when oxidising an alcohol to a ketone ?

A

Aqueous solution of acidified potassium dichromate (VI)

62
Q

What is the general formula for oxidising an alcohol to a ketone ?

A

R1CH(OH)R2 + [o] - R1COR2 +H2O

63
Q

Outline the oxidisation of tertiary alcohols.

A

Tertiary alcohols cannot be oxidised in the same way as primary and secondary alcohols. This because a hydrogen atom is not available on the adjacent carbon atom to the hydroxyl group.

64
Q

Why are tertiary alcohols difficult to oxidise ?

A

Because a hydrogen atom is not available on the adjacent carbon atom to the hydroxyl group.

65
Q

Name the 2 identification tests for aldehydes.

A

Tollen’s silver mirror test

Benedicts/ Fehlings reagent

66
Q

Outline how tollens test is carried out and why it works.

A

Silver nitrate in ammonia (-AgNO3|NH3(am))

Add a few drops of the reagent to the supposed aldehyde solution and boil.
If it turns to a silver mirror, aldehyde is present because when colourless silver ions reduces to solid metallic silver. This occurs when the aldehyde is oxidised.

67
Q

What is in Tollen’s reagent ?

A

Silver nitrate in ammonia

-AgNO3/NH3 (aq)

68
Q

What are the components of benedicts / fehlings reagent ?

A

Complex copper 2 ion solution.

69
Q

How is Benedicts / Fehlings test carried out ? And why does this work ?

A

Add drops of the benedicts reagent to the supposed aldehyde.
If the aldehyde is present, the solution will turn from blue to brick red and form a precipitate. Oxidisation of the aldehyde reduces Copper2 to Copper1 ions.

70
Q

How can you ensure production of a carboxylic acid by oxidising primary alcohols ?

A

Perform a reflux with excess reagent ( aqueous solution of acidified potassium dichromate VI).

71
Q

What is the indicator that a complete oxidisation to create a carboxylic acid has occurred ? What

A

When oxidising is complete, potassium dichromate solution will turn from orange to green.

72
Q

How can carboxylic acids be tested for ?

A

Add sodium carbonate (Na2CO3).
If the solution begins to fizz acid is present because carbon dioxide has been produced and this causes the immediate fizzing.

73
Q

Why must a reaction flask be in cold water when oxidising a primary alcohol to an aldehyde ?

A

Aldehydes have low boiling points so must be kept cool to prevent volatile gases escaping.

74
Q

Why are aldehydes and ketones less volatile than alcohols and carboxylic acids ?

A

Alcohols and carboxylic acids have intermolculae hydrogen bonding which is stronger that the dipole dipole bonding in alcohols and carboxylic acids.

75
Q

Draw the reaction for oxidising a primary alcohol to a aldehyde.

A

In notes

76
Q

Draw the reaction for oxidising a aldehyde to a carboxylic acid.

A

Notes.

77
Q

How does potassium dichromate solution affect a primary alcohol ?

A

Potassium dichromate turns from orange to green

78
Q

How does potassium dichromate solution affect a secondary alcohol ?

A

Turns from orange to green

79
Q

How does potassium dichromate solution affect a aldehyde ?

A

Turns from orange to green.

80
Q

How does an aldehyde affect tollens solution ?

A

Silver mirror created.

81
Q

How does Fehlings solution affect an aldehyde ?

A

Turns from blue to brick red

82
Q

How does sodium carbonate affect an acid.

A

Fizzing.

Chemistry (27 decks)

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