Alcohols

Question 1

Primary, secondary, tertiary alcohol

Answer 1

1° - carbon carrying -OH only attached to one alkyl group

Question 2

How can alcohols form alkenes

Answer 2

Dehydration reaction- eliminate water
-heated with conc sulfuric acid catalyst
+ allows produce alkene from renewable resource (alcohol from fermentation)
+polymers without oil

Question 3

How to produce alkene from alcohol

Answer 3

Distillation-
-add conc H2SO4 + H3PO4 to round bottom flask containing cyclohexanol, add carborundum boiling chipe, swirl
-gently heat water bath
-chemicals evaporate, into condenser, turn to liquid
-collect in cooled flask
Separation-
-will contain impurities
-separating funnel, add water to dissolve soluble impurities
-allow mixture settle into layers, drain aqueous lower layer, leave impure cyclohexene
Purification-
-drain into round bottom flask
-add anhydrous CaCl2 add bung, leave to dry
-distil ahain

Question 4

Hydration to form alcohol conditions

Answer 4

-react ethane with steam to produce ethanol
-300°C
-60atm
H3PO4 catalyst

Question 5

Hydration properties

Answer 5

• non renewable
• continuous process
• not carbon neutral
• fast
• pure product (100%)

Question 6

Fermentation conditions

Answer 6

Sugar from plant material (glucose) converted to ethanol and CO2 by fermentation

• 35°C (optimum temp for yeast)
• yeast catalyst
• atmospheric

Question 7

Fermentation properties

Answer 7

• renewable- sugar
• batch process
• carbon neutral
• slow
• impure product (15%): fractional distillation needed

Question 8

Biofuel

Answer 8

A fuel made from biological material that’s recently died

Question 9

How is fermentation carbon neutral?

Answer 9

The CO2 released when the fuel is burnt is equal to the CO2 absorbed by plants

Question 10

Advantages and drawbacks of biofuels over fossil fuels

Answer 10

+renewable (won’t run out) so more sustainable
+carbon neutral
-petrol car engines must be modified to use fuels with high ethanol conc
-less land to grow food (crops take up space) so harder to feed

Question 11

Equations to support carbon neutral

Answer 11

Photosynthesis-
6CO2 + 6H2O —> C6H12O6 + 6O2
Fermentation-
C6H12O6 —> 2C2H5OH + 2CO2
combustion of ethanol-
2C2H5OH + 6O2 —> 4CO2 + 6H2O

Question 12

How is it not completely carbon neutral?

Answer 12

Fossil fuels burnt to power machinery used to make fertiliser, harvesting crops, refine + transport bio ethanol
-produces carbon dioxide

Question 13

Oxidising agent

Answer 13

[o]= acidified potassium dichromate

Question 14

What are alcohols oxidised to?

Answer 14

Primary alcohol - aldehyde - carboxylic acid (p-a= distillation, p-c= reflux)
Secondary alcohol - ketone (reflux)
Tertiary alcohol- not easily oxidised

Question 15

How can you tell if it’s been oxidised

Answer 15

Orange dichromate ion reduced to green chromium ion
Primary + secondary- will change from orange solution to green solution
Tertiary- will remain orange solution

Question 16

What are aldehydes

Answer 16

• H and one alkyl group attached to carbonyl C atom
  -al
  -C=O
  |
  H
  -C in -CHO group always counted as 1st carbon

Question 17

What are ketones

Answer 17

• 2 alkyl groups attached to carbonyl C atom
• one
• C=O in middle of carbon chain

Question 18

What are carboxylic acids

Answer 18

-COOH group at end of carbon chain
-oic acid
-C=O
|
O-H
-C in COOH counted as 1st

Question 19

How can aldehydes and ketones be distinguished

Answer 19

-Weak oxidising agents can be used to distinguish between an aldehyde and a ketone
The aldehyde will be oxidised to a carboxylic acid, but the ketone will not undergo oxidation
-If an aldehyde is warmed with Fehling’s solution, the aldehyde will be oxidised and a colour change will take place: blue- brick red precipitate
-If gently warmed with Tollens’ reagent, an aldehyde will become oxidised- silver mirror