3.5 Alcohols

Question 1

What are primary, secondary and tertiary alcohols

Answer 1

• primary: 1 other carbon attached to the carbon to which the -OH is bonded
• secondary: 2 other carbons are attached to the carbon the OH is bonded to
  -tertiary: 3 other carbons are bonded to the carbon with the OH bonded

Question 2

What is an aldehyde?

Answer 2

Adds CHO to the end of the molecular formula and adds ‘al’ to the name
R-c=O and -H

Question 3

What is a keytone?

Answer 3

Adds =O to the molecular formula and ‘one to the name

Question 4

What is a carboxylic acid?

Answer 4

Adds COOH to the molecular formula and adds ‘oic acid’ to the name

Question 5

What is a hydroxi?

Answer 5

Name for an alcohol when there is a higher priority group involved

Question 6

What is it when something ends ‘diol’?

Answer 6

Two alcohols groups attached

Question 7

Explain and draw how primary alcohols are oxidised

Answer 7

• oxidised into aldehydes
• further oxidation into carboxylic acid

Question 8

Explain and draw what happens when a secondary alcohol is oxidised

Answer 8

• forms keytone
• can’t be further oxidised

Question 9

Explain what happens when a tertiary alcohol is oxidised

Answer 9

• can not be oxidised
• that involced breaking and C-C bond rather than a C-H bond
• requires more energy

Question 10

What is distillation and reflux definitions

Answer 10

Distillation - using heat and vapours are condensed and collected immediately
Reflux - continuous heating of the sample where the vapours are condensed and return back to the vessel (used to make a carboxylic acid from a primary alcohol)

Question 11

Why are anti bumping granules used during distillation/reflux?

Answer 11

They prevent larger bubbles, which could travel up the equipment during distillation and contaminate the cylinder.
They do this by breaking up larger bubbles into smaller ones

Question 12

Describe what happens during oxidation of a primary alcohol with acidified potassium dicromate

Answer 12

If distilled, Dicromate ion is orange so the solution (containing colourless alcohol) starts as orange.
As alcohol is oxidised, solution changes colour as cromium is produced (which is green).
If refluxed, carboxylic acid should be produced.
Test by adding it to sodium hydrocarbonate and bubbling it through lime water: should turn cloudy
Universal indicator should go yellow

Question 13

What are the key points of eliminations of alcohols

Answer 13

• H+ produced must be from a C adjacent to the C with the O-H
• done is a concentrated solution of sulphuric acid H2SO4 because H+ is needed
• H+ acts as a catalyst because it is regenerated

Question 14

Name the two ways of producing ethanol

Answer 14

Fermentation and industrially (cracking)

Question 15

Describe fermentation

Answer 15

Anaerobic respiration uses enzymes from yeast
Conditions : 35°c, air kept out to prevent aerobic respiration
C6H12O6(aq) —> 2C2H5OH(aq) + CO2(g)

Question 16

Describe producing ethanol industrially

Answer 16

React ethene (made by cracking crude oil) with steam and phosphoric acid

Question 17

Describe the difference between producing ethanol from fermentation or industrially

Answer 17

Industrially : fast, continuous, virtually pure, non renewable source (oil)
Fermentation: slow, batch, aqueous solution of ethanol is produced, renewable (sugar)

Question 18

What is biofuel

Answer 18

Any fuel taken from living or recently living organisms + it is carbon neutral as it takes in carbon in photosynthesis and releases carbon when produced or burnt
Bioethanol is popularly used as fuel in countries that grow a lot of glucose

Question 19

Describe tollens reagent

Answer 19

Contains Ag+ ions which is reduced to silver as oxidation takes place. This only works for an aldehyde as keytones can’t be oxidised

Question 20

Describe fehlings tests

Answer 20

Blue copper ions will oxidise aldehydes creating brick red precipitate