Alcohols

Question 1

What is the alcohol functional group?

Answer 1

⦾ -OH group

Question 2

What is the general formula for alcohols?

Answer 2

⦾ CnH2n+1

Question 3

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

Answer 3

⦾ Which C -OH bonded to

Question 4

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

Answer 4

⦾ C with 1 alkyl group

Question 5

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

Answer 5

⦾ C with 2 alkyl groups

Question 6

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

Answer 6

⦾ C with 3 alkyl groups

Question 7

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

Answer 7

⦾ pg. 226

Question 8

What are the 2 main methods for producing alcohols?

Answer 8

⦾ Hydration of alkenes

⦾ Fermentation

Question 9

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

Answer 9

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

Question 10

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

Answer 10

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

Question 11

What is the reaction yield?

Answer 11

⦾ Low - 5%

⦾ BUT - recycle unreacted ethene - ~95%

Question 12

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

Answer 12

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

Question 13

Explain fermentation?

Answer 13

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

Question 14

Is fermentation exothermic or endothermic?

Answer 14

⦾ Exothermic

Question 15

What are the reaction conditions for the fermentation of yeast?

Answer 15

⦾ Anaerobic conditions

⦾ Optimum temp - 30C - 40C

Question 16

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

Answer 16

C6H12O6(aq) → 2C2H5OH(aq) + 2CO2(aq)

Question 17

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

Answer 17

⦾ …dies,

Question 18

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

Answer 18

⦾ Fractional distillation - purify ethanol

Question 19

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

Answer 19

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

Question 20

Define biofuel?

Answer 20

⦾ Fuel made from recently dead biological material

Question 21

What are the advantages of biofuel?

Answer 21

1 ⦾ More sustainable than crude oil - renewable

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

Question 22

What are the disadvantages of biofuel?

Answer 22

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.

Question 23

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

Answer 23

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

Question 24

Do these equation support that carbon is a neutral fuel?

Answer 24

⦾ All species in equations cancel each other out

⦾ CO2 neither take in/out of environment

Question 25

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

Answer 25

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

Question 26

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

Answer 26

⦾ Primary | ⦾ Secondary

Question 27

Explain the full oxidation of primary alcohols? | Include equations

Answer 27

⦾ 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

Question 28

Explain the full oxidation of secondary alcohols? | Include equations

Answer 28

⦾ Heat in presence of acidified potassium dichromate | ⦾ Produce ketones

Question 29

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

Answer 29

⦾ K2Cr2O7 - Potassium dichromate

Question 30

What is the colour change when an alcohol is oxidised?

Answer 30

⦾ Orange to Green

Question 31

What ion is reduced the reaction? (include colours)

Answer 31

⦾ Orange dichromate (VI) ion Cr2O7 2- | ⦾ Reduced to green Chromium ion, Cr3+

Question 32

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 ________ ____?

Answer 32

⦾ 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

Question 33

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

Answer 33

``` ⦾ 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 ```

Question 34

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

Answer 34

⦾ Reflux with acidified dichromate(VI) to produce ketone | ⦾ Ketones not easily oxidised so prolonged refluxing won't produce anything more.

Question 35

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

Answer 35

⦾ Fehling's/Benedicts solution | ⦾ Tollen's reagent

Question 36

What is Fehling's/Benedicts solution?

Answer 36

⦾ Deep blue Cu+ complex | ⦾ Alkaline solutions of Cu(II)sulfate

Question 37

What is Tollen's reagent?

Answer 37

⦾ Colourless | ⦾ [Ag(NH3)2]+ complex

Question 38

Which is easily oxidised from ketones and aldehydes?

Answer 38

⦾ Aldehydes

Question 39

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

Answer 39

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

Question 40

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

Answer 40

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