Alcohols

Question 1

Predict and explain the relative boiling point of hexan-1-ol and heptane: (4)

Answer 1

• similar strenght VdW forces betw/ molecules bcs similar no. of electrons
• hexan-1-ol also has H bonding betw/ molecules
• so will require more energy to overcome the IMF betw/ neighbouring molecules of hexan-1-ol
• so higher M.P.

Question 2

Cyclohexene is prepared by the dehydration of cyclohexanol using concentrated phosphoric acid as a catalyst. The structure of concentrated phosphoric acid is shown.
‘’’’’‘OH
O= P - OH
‘’’’’‘OH
Identify the factors that influence the boiling points of each of the compounds in this reaction mixture. State how and explain why cyclohexene can be separated from the reaction mixture. (6)

Answer 2

• cyclohexene : van der Waals’ (between molecules)
• cyclohexanol : hydrogen bonds (between molecules)
• phosphoric acid: hydrogen bonds (between molecules)
• idea that cyclohexene has weakest forces
• separated by (simple / fractional) distillation

Question 3

Naming alcohols

Answer 3

If there are two or more -OH groups then di, tri are used.
Add the ‘e’ on to the stem name though
eg. propane-1,2,3-triol

Question 4

the functional group of alcohols:

Answer 4

C-O-H

Question 5

if there are 2 or more alcohols:

Answer 5

di, tri, tetra…
add ‘e’ onto the stem name though! eg. ethane-1,2-diol

Question 6

Functional group of aldehyde:

Answer 6

C=O
I
H

Aldehydes always have a C=O on the first C so don’t need a number l

Question 7

Thermometer placement during distillation:

Answer 7

The bulb of the thermometer should be at
the T junction connecting to the
condenser to measure the correct boiling
point.
BECAUSE we are measuring temp of vapour not the solution.

Question 8

Partial oxidation of Primary alcohols:

Answer 8

Reaction: primary alcohol -> aldehyde
Reagent: potassium dichromate (VI) solution and dilute sulfuric acid.
Conditions: (use a limited amount of dichromate) warm gently and distil out the aldehyde as it forms:

Question 8

Ethanol from ethene dis/advantages:

Answer 8

Advantages:
* faster reaction
* purer product
* continuous process (which means cheaper manpower)
Disadvantages:
* high technology equipment needed (expensive initial costs)
* ethene is non-renewable resource (will become more expensive when raw materials run out)
* high energy costs for pumping to produce high pressures

Question 8

Fermentation to prod. ethanol dis/advantages:

Answer 8

Advantages
* sugar is a renewable resource
* production uses low level technology / cheap
equipment

Disadvantages
* batch process which is slow and gives high production
costs
* ethanol made is not pure and needs purifying by
fractional distillation
* depletes land used for growing food crops

Question 9

Essential Conditions to prod. ethanol from ethene:

Answer 9

• high temperature 300 °C
• high pressure 70 atm
• strong acidic catalyst of concentrated H3PO4

Question 10

Oxidation of 2ndary alcohols forms:

Answer 10

Ketones
functional group: C=O but NOT at a terminal end else its an aldehyde

Question 11

Observation when a 2ndary alcohol is reduced to to form a ketone:

Answer 11

Observation: the orange dichromate ion (Cr2O72-) reduces to the green Cr^3+ ion

Question 12

The prescence of carboxylic acid can be detected by:

Answer 12

• Na2CO3
• fizz and produce bubbles (effervescence)

Question 13

why is making alkenes through dehydration of alcohols important?

Answer 13

Producing alkenes from alcohols provides a possible route to polymers without using monomers derived from oil.

Question 14

Why can’t tertiary alcohols be oxidised?

Answer 14

no H atom bonded to C containing -OH group

Question 15

test to distinguish between ketone and carboxylic acid and observation: (3)

Answer 15

• NaHCO3
• ketone : no visible change
• carboxylic acid: effervescence / fizzing

Question 16

test to distinguish between ketone and aldehyde and observations (3):

Answer 16

• Fehling’s solution
• ketone: no visible change
• aldehyde: red solid forms