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Chemistry > Alcohols > Flashcards

Alcohols Flashcards

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1
Q

What is the general formula of alcohols?

A

CnH2n+1OH

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2
Q

Why do alcohols have a higher melting and boiling point than alkanes of similar chain length? (1)

A

Because alcohols have an OH group they have hydrogen bonding between molecule so higher melting and boiling point

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3
Q

Why do short alcohol molecules dissolve well in polar solvents but longer alcohol molecules dissolve better in non-polar solvents? (1)

A

Because hydrogen bonds form about the OH group but not about the non-polar alkyl chain of the molecule

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4
Q

What are some of the uses of ethanol? (5)

A

As an intermediate in the synthesis of other organic chemicals
As a solvent in cosmetics and perfumes
In the manufacture of drugs, detergents and inks
The alcohol found in alcoholic drinks
Biofuel

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5
Q

What is the name of the reaction that is used to produce ethanol from crude oil?

A

Hydration of ethene

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6
Q

What conditions are needed for hydration? (4)

A

Concentrated phosphoric (H3PO4) catalyst
Steam
450 degrees Celsius temperature
50-100 atm pressure

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7
Q

Hydration occurs via which mechanism?

A

Electrophilic addition

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8
Q

What is the reaction called which produces ethanol by fermentation?

A

Anaerobic respiration/fermentation

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9
Q

What are the conditions needed for fermentation? (3)

A

Yeast enzymes
Temp - 35 degrees Celsius
No oxygen

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10
Q

Why should no oxygen be present when producing ethanol from fermentation? (1)

A

Because the ethanol formed may oxidise to ethanoic acid

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11
Q

What are the advantages of hydration of ethene to produce ethanol? (5)

A

Large scale production method
High purity product made
Readily available raw material
High rate of reaction
Continuous production method

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12
Q

What are the disadvantages of hydration of ethene? (3)

A

High temperature and pressure needed which increases costs
Expensive and high tech equipment needed
Crude oil is non-renewable

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13
Q

What are the advantages of fermentation? (4)

A

Uses renewable resources
Low tech method so suitable for developing countries as little expensive equipment needed
Low costs
Low temperature needed

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14
Q

What are the disadvantages of fermentation? (5)

A

Slow rate of reaction
Impure ethanol made needs distilling
Causes food prices to rise if crops are used to produce alcohol instead of food
Batch production method so less efficient
Low atom economy

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15
Q

What are biofuels?

A

A fuel produced from renewable plant material

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16
Q

What are the advantages of biofuels? (5)

A

Can be considered to be carbon neutral
Come from renewable raw materials
Helps to conserve crude oil supplies
Provide employment for farmers to grow crops
Companies with no oil reserves can still generate their own fuel

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17
Q

What are the disadvantages of biofuels? (4)

A

There are many other carbon costs in their production meaning they are not carbon neutral
Food prices rise as crops used for biofuels therefore an increase market price
Supply of biofuels dependent on crop harvest so less reliable
Biofuels cannot be made on a scale to meet global demands for fuels

18
Q

What is the most common oxidising agent for alcohols?

A

Acidified potassium dichromate

19
Q

What are primary alcohols oxidised to and what are the conditions needed? (4)

A

Aldehydes
Dilute H2SO4
Potassium dichromate
Distillation

20
Q

What is the observation when primary alcohols are oxidised to aldehydes under distillation?

A

Orange to green

21
Q

Outline the process of distillation (6)

A

Turn the water supply on to the condenser
Heat the flask
Ethanol will vaporise
Use a thermometer to maintain the temperature at the boiling point of ethanal
The ethanol vapours condense back into a liquid in the condenser
The ethanol is collected in a cooled container to avoid it vaporising

22
Q

How do primary alcohols produce carboxylic acids? (4)

A

Oxidation
Conc H2SO4
Potassium dichromate
Reflux

23
Q

What is the observation when primary alcohols are oxidised to carboxylic acid under reflux?

A

Changes from orange to green

24
Q

Outline the process of reflux (5)

A

Connect the condenser vertically and turn the water supply on
Heat the flask
Ethanal will form by oxidation and will vaporise
The ethanal will condense on the side of the condenser and fall back into the reaction container
The ethanal will oxidise again to form ethanoic acid

25
Q

Why is reflux used to oxidise an alcohol into a carboxylic acid?

A

Reflux doesn’t allow any reactant vapour to escape

26
Q

What are secondary alcohols oxidised to and what are the conditions? (4)

A

Ketones
Conc H2SO4
Acidified potassium dichromate
Reflux

27
Q

What is the observation when secondary alcohols are oxidised to ketones under reflux?

A

Changes from orange to green

28
Q

Why is reflux used to oxidise an alcohol into a ketone and why? (2)

A

No risk of oxidising the ketone further in error
Because carbon-carbon bond would have to break

29
Q

What are the conditions of silver mirror test?

A

Warm gently

30
Q

What is the observation of silver mirror test with aldehydes? (2)

A

Aldehydes - Silver mirror forms
Ketones - NVC

31
Q

Conditions of Fehling’s test and observations (3)

A

Warm gently
Aldehydes - Blue solution to brick red precipitate
Ketones - NVC

32
Q

Test for carboxylic acids and the conditions required and the observation? (3)

A

Sodium Carbonate
Condition - room temperature
Observation - effervescence

33
Q

Name of mechanism to form alkenes from alcohols and conditions (2)

A

Elimination
Hot, concentrated H2SO4

34
Q

What intermolecular forces does propanal have

A

Dipole-Dipole

35
Q

Suggest one advantage and one disadvantage for industry of carrying out the fermentation of glucose to produce ethanol at 35 degrees Celsius and not 25 degrees Celsius (2)

A

Advantage - ethanol produced at a faster rate
Disadvantage - more energy required in the reaction

36
Q

Fermentation of glucose to produce ethanol would result in ethanol being contaminated by ethanoic acid
How does this contamination occur? (1)

A

Oxidation occurs

37
Q

Write an equation for the fermentation of glucose to produce ethanol (1)

A

C6H12O6 —> 2C2H5OH + 2CO2

38
Q

Explain how using ethanol in petrol engines could be considered to be carbon neutral (1)

A

CO2 released in fermentation and combustion = CO2 absorbed when growing

39
Q

Explain why using ethanol in petrol engines could not be considered to be carbon neutral (1)

A

Other ‘carbon costs’ associated with it e.g. transport

40
Q

What is an elimination reaction (1)

A

Removal of a smaller molecule from a larger one

41
Q

What is in Tollen’s reagent and how does this react with the substance to be tested (2)

A

Silver nitrate in NH3 - oxidises aldehydes but not ketones
Complex silver (I) reduced to Ag

42
Q

What is in Fehling’s solution and how does this react with the substance to be tested (2)

A

Blue copper (II) complex ions - gentle oxidising agent
Reduced to Cu+ ions

Chemistry (28 decks)

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