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CHEMISTRY (AS) > Alcohols > Flashcards

Alcohols Flashcards

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1
Q

What is the alcohol functional group?

A

⦾ -OH group

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2
Q

What is the general formula for alcohols?

A

⦾ CnH2n+1

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3
Q

What does whether an alcohol is primary, secondary or tertairy depend on?

A

⦾ Which C -OH bonded to

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4
Q

Which C is the -OH bonded to in primary alcohols?

A

⦾ C with 1 alkyl group

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5
Q

Which C is the -OH bonded to in secondary alcohols?

A

⦾ C with 2 alkyl groups

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6
Q

Which C is the -OH bonded to in tertiary alcohols?

A

⦾ C with 3 alkyl groups

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7
Q

Draw out the general structure (with R groups) for primary, secondary and tertiary alcohols?

A

⦾ pg. 226

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8
Q

What are the 2 main methods for producing alcohols?

A

⦾ Hydration of alkenes

⦾ Fermentation

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9
Q

What are the reaction conditions for the hydration of alkenes to produce alcohol?

A 
⦾ Steam
⦾ Acid catalyst - solid phosphoric (V) acid 
⦾ Aqueous cond.
⦾ 300C
⦾ High pressures (60atm)
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10
Q

What is the equation (+ conditions) for the industrial hydration of ethene to produce alcohol?

A

⦾ CH2=CH2(g) + H2O(g) + H3PO4 + 300C + 6atm → CH3CH2OH(g)

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11
Q

What is the reaction yield?

A

⦾ Low - 5%

⦾ BUT - recycle unreacted ethene - ~95%

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12
Q

Draw out the reaction mechanism for the reaction of steam with ethene?

A

1 ⦾ Pair of e- from C=C bonds with H+ from acid
2 ⦾ Lone e- pair from water bonds to carbocation
3 ⦾ Water loses a H+
4 ⦾ Alcohol formed

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13
Q

Explain fermentation?

A

⦾ Yeast
⦾ Enzymes break down starch from crops into sugars
⦾ Sugars fermented to form alcohol

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14
Q

Is fermentation exothermic or endothermic?

A

⦾ Exothermic

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15
Q

What are the reaction conditions for the fermentation of yeast?

A

⦾ Anaerobic conditions

⦾ Optimum temp - 30C - 40C

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16
Q

What is the equation for the reaction of glucose to ethanol?

A

C6H12O6(aq) → 2C2H5OH(aq) + 2CO2(aq)

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17
Q

When the solution reaches about 15% ethanol, the yeast…

A

⦾ …dies,

18
Q

Which method/equipment can be used to increase the concentration of ethanol?

A

⦾ Fractional distillation - purify ethanol

19
Q

Compare the advantages and disadvantages of the 2 main ethanol production methods?

A

Hydration of Ethene:
⦾ ROR - V. fast
⦾ Quality of product - Pure
⦾ Raw material - Ethene from oil - finite resource
⦾ Process/Costs - Continous - expensive equipment needed - low labor costs

Fermentation:
⦾ ROR - V. slow
⦾ Quality of product - V. impure - needs more processing
⦾ Raw material - Sugars - renewable
⦾ Processes/Costs - Batch process - cheap equipment needed - high labor costs

20
Q

Define biofuel?

A

⦾ Fuel made from recently dead biological material

21
Q

What are the advantages of biofuel?

A

1 ⦾ More sustainable than crude oil - renewable

2 ⦾ Carbon neutral - Burnt crop releases same amount taken in when growing.

22
Q

What are the disadvantages of biofuel?

A

1 ⦾ Ethical “Food vs Fuel” - land of crops burnt not fed
2 ⦾ Environmental Deforestation - land clearing removes trees that take in CO2 and are burnt
3 ⦾ Fertilisers added to soils may pollute waterways or releas NO2 (GHG)
4 ⦾ Switching from FFs to biofuel - most cars unable to run.

23
Q

Write and explain the equations for whether is a carbon neutral fuel?

A 
1 ⦾ Photosynthesis:
6CO2 + 6H2O → C6H12O6 + 6O2
2 ⦾ Fermentation:
C6H12O6 → 2C2H5OH + 2CO2
Ethanol burned
3 ⦾ 2C2H5OH + 6CO2 → 4CO2 + 6H2O
24
Q

Do these equation support that carbon is a neutral fuel?

A

⦾ All species in equations cancel each other out

⦾ CO2 neither take in/out of environment

25
Q

Explain why bioethanol isn’t a completely carbon neutral fuel?

A

⦾ FFs need to be burnt to power machinery to make fertilisers
⦾ Refinining + transport uses FFs

26
Q

Which of the following: primary, seconday and tertiary alcohols can be oxidised to produce products?

A

⦾ Primary

⦾ Secondary

27
Q

Explain the full oxidation of primary alcohols?

Include equations

A

⦾ Heat in presence of acidified potassium dichromate
⦾ Distill to produce aldehydes
ethanol + [O] + K2Cr2O7 → Ethanal + H2O

⦾ Heat further under reflux
⦾ Produce carboxylic acids
Ethanal + [O] → Ethanoic acid + H2O

28
Q

Explain the full oxidation of secondary alcohols?

Include equations

A

⦾ Heat in presence of acidified potassium dichromate

⦾ Produce ketones

29
Q

What is the oxidising agent used in the oxidation of alcohols?

A

⦾ K2Cr2O7 - Potassium dichromate

30
Q

What is the colour change when an alcohol is oxidised?

A

⦾ Orange to Green

31
Q

What ion is reduced the reaction? (include colours)

A

⦾ Orange dichromate (VI) ion Cr2O7 2-

⦾ Reduced to green Chromium ion, Cr3+

32
Q

What are the conditions for the initial oxidation of primary alcohols?
What is its hard to control?
What are the methods to prevent it reacting further into ________ ____?

A

⦾ Gently heat ethanol with potassium dichromate (VI) solution + sulfuric acid in test tube
⦾ “apple” smelling ethanal produced
⦾ Hard to control heat amount
⦾ Aldehyde oxidised more to “vinegar” ethanoic acid
⦾ Get aldehyde out of [O] solution as soon as formed - gently heat excess alcohol with controlled amount of [O] in distillation apparatus
⦾ Aldehyde has lower bp. than alcohol distills off quick

33
Q

What are the reaction conditions for the second part of oxidising alcohols?

A 
⦾ Vigorously [O} alcohol
⦾ Mix with excess [O]
⦾ Heat under reflux
⦾ Vaporised compounds cooled, condense back into reaction mixture 
⦾ Aldehyde stays in reaction mixture 
⦾ Further [O] to carboxylic acid
34
Q

What are the reaction conditions for the oxidation of secondary alcohols?

A

⦾ Reflux with acidified dichromate(VI) to produce ketone

⦾ Ketones not easily oxidised so prolonged refluxing won’t produce anything more.

35
Q

Which 2 solutions can be used to test for aldehydes and ketones?

A

⦾ Fehling’s/Benedicts solution

⦾ Tollen’s reagent

36
Q

What is Fehling’s/Benedicts solution?

A

⦾ Deep blue Cu+ complex

⦾ Alkaline solutions of Cu(II)sulfate

37
Q

What is Tollen’s reagent?

A

⦾ Colourless

⦾ [Ag(NH3)2]+ complex

38
Q

Which is easily oxidised from ketones and aldehydes?

A

⦾ Aldehydes

39
Q

How can Fehling’s solution be used to distinguish between Aldehydes and Ketones?

A

⦾ Warm with aldehyde
⦾ Reduce to brick-red Cu2O prec.
⦾ Stays blue with ketone

40
Q

How can Tollen’s reagent be used to distinguish between Aldehydes and Ketones?

A

⦾ Warm with aldehyde
⦾ Reduced to silver - silver mirror
⦾ Remains colourless with ketone

CHEMISTRY (AS) (24 decks)

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