AQA A level Organic Chemistry I

This question is about the preparation of 2,3,3-trimethylbut-1-ene.

The preparation is done by heating the alcohol with concentrated phosphoric acid, that acts as a catalyst. The figure below shows the apparatus used.

The distillate is collected in the range 77–82 °C (a) Explain why the water should enter the condenser at the bottom and not at the top(2)

it ensures the condenser is filled with water (1)

condenser is cooler (1)

In Europe, some of the glucose from crops is fermented to produce ethanol.

Use of a carbon-neutral fuel leads to no net emissions of carbon dioxide to the

atmosphere.

The ethanol produced by fermentation of glucose may be regarded as a

carbon-neutral fuel.

Justify this statement. Include the relevant chemical equations in your

answer. (4)

6CO₂ + 6H₂O → C₆H₁₂O₆ + 6O₂ (1)

C₆H₁₂O₆ → 2C₂H₅OH + 2CO₂ (1)

2C₂H₅OH+6O₂ → 4CO₂+6H₂O (1)

formation of C₆H₁₂O₆ takes in 6CO₂ and fermentation and combustion of ethanol gives out 6CO₂ (1)

Coffee beans from South America are exported to Europe in an outer layer

called silverskin.

The waste silverskin can be fermented to produce a solution containing

propanone, ethanol and butan-1-ol.

Suggest why ethanol produced in Europe using silverskin from South

America is less likely to be carbon-neutral than ethanol produced from

crops grown in Europe. (1)

transport (from South America to Europe) produces CO₂ / has C emissions / has larger C footprint (1)

Butan-1-ol can be manufactured by reacting steam with but-1-ene in the

presence of the catalyst, concentrated sulfuric acid.

In the first part of this process, but-1-ene reacts with concentrated sulfuric acid to

form compounds W and X

There is a very low yield of butan-1-ol from but-1-ene in this manufacturing process. Explain why (2)

formed from less stable carbocation (1)

formed from primary rather than secondary carbocation (1)

This question is about the preparation of hexan-2-ol.

Hexan-2-ol does not mix with water and has a boiling point of 140 ^oC

Hexan-2-ol can be prepared from hex-1-ene using this method.

a Measure out 11.0 cm³ of hex-1-ene into a boiling tube in an ice bath.

b Carefully add 5 cm³ of concentrated phosphoric acid to the hex-1-ene.

c After 5 minutes add 10 cm³ of distilled water to the mixture and transfer the

boiling tube contents to a separating funnel.

d Shake the mixture and allow it to settle.

e Discard the lower (aqueous) layer.

f Add a fresh 10 cm³ sample of distilled water and repeat steps d and e.

g Transfer the remaining liquid to a beaker.

h Add 2 g of anhydrous magnesium sulfate and allow to stand for 5 minutes.

i Filter the mixture under reduced pressure.

j Distil the filtrate and collect the distillate that boils in the range 130–160 ^oC

It is important to wear eye protection and a lab coat when completing this

experiment.

Suggest, with a reason, one other appropriate safety precaution for this

experiment. (2)

Wear gloves (1)

concentrated phosphoric acid is corrosive (1)

This question is about the preparation of hexan-2-ol.

Hexan-2-ol does not mix with water and has a boiling point of 140 ^oC

Hexan-2-ol can be prepared from hex-1-ene using this method.

a Measure out 11.0 cm³ of hex-1-ene into a boiling tube in an ice bath.

b Carefully add 5 cm³ of concentrated phosphoric acid to the hex-1-ene.

c After 5 minutes add 10 cm³ of distilled water to the mixture and transfer the

boiling tube contents to a separating funnel.

d Shake the mixture and allow it to settle.

e Discard the lower (aqueous) layer.

f Add a fresh 10 cm³ sample of distilled water and repeat steps d and e.

g Transfer the remaining liquid to a beaker.

h Add 2 g of anhydrous magnesium sulfate and allow to stand for 5 minutes.

i Filter the mixture under reduced pressure.

j Distil the filtrate and collect the distillate that boils in the range 130–160 ^oC

Give a reason for adding the distilled water in steps c and f (1)

to remove (water) soluble impurities (1)

This question is about the preparation of hexan-2-ol.

Hexan-2-ol does not mix with water and has a boiling point of 140 ^oC

Hexan-2-ol can be prepared from hex-1-ene using this method.

a Measure out 11.0 cm³ of hex-1-ene into a boiling tube in an ice bath.

b Carefully add 5 cm³ of concentrated phosphoric acid to the hex-1-ene.

c After 5 minutes add 10 cm³ of distilled water to the mixture and transfer the

boiling tube contents to a separating funnel.

d Shake the mixture and allow it to settle.

e Discard the lower (aqueous) layer.

f Add a fresh 10 cm³ sample of distilled water and repeat steps d and e.

g Transfer the remaining liquid to a beaker.

h Add 2 g of anhydrous magnesium sulfate and allow to stand for 5 minutes.

i Filter the mixture under reduced pressure.

j Distil the filtrate and collect the distillate that boils in the range 130–160 ^oC

Give a reason for adding anhydrous magnesium sulfate in step h. (1)

To remove water / absorb water / dry the liquid (1)