Chapter 16: Organic Analysis

Question 1

Alkanes

Answer 1

general functional group: CnH2n+2

suffix: -ane
example: ethane

Question 2

Alkenes

Answer 2

general functional group: R-CH=CH-R

suffix: -ene
example: ethene

Question 3

Halogenoalkanes

Answer 3

general functional group: R - X (X= F, Cl, Br or I)

suffix: none
example: chloromethane

Question 4

Alcohols

Answer 4

general functional group: R - OH

suffix: -ol
example: ethanol

Question 5

*Aldehydes

Answer 5

general functional group: R - C=O
I
H
suffix: -al
example: ethanal (CH3CHO)

Question 6

*Ketones

Answer 6

general functional group: R- C -R’
II
O
suffix: -one
example: propanone (CH3COCH3)

Question 7

*Carboxylic Acids

Answer 7

general functional group: R- C =O
I
OH
suffix: -oic acid
example: propanoic acid (CH3COOH)

Question 8

Test for alkenes

Answer 8

Test: shake with bromine water
Result: bromine water decolourises, and orange solution goes colourless
Reaction: addition

Question 9

Testing for alcohols

Answer 9

• Primary alcohol + [O] -> Aldehyde + H2O (distillation)
• Secondary alcohol + [O] -> Ketone + H2O (reflux; acidic conditions)
• Tertiary alcohol + [O] -> no reaction

Test: add warm acidified potassium dichromate (VI)
Result: primary alcohol and secondary alcohol will turn from orange solution to green solution. Tertiary alcohol remains orange.
Reaction: oxidation (not for tertiary alcohol)
(dichromate acts as oxidising agent and will therefore be reduced)

Question 10

Testing for aldehydes

Answer 10

Option 1:
Test: Fehling’s solution (condition: warm)
Result: blue (Cu2+ present) -> green -> brick red precipitate formed (Cu2O)
Reaction: oxidation (carboxylic acid produced)

Option 2:
Test: Tollens’ reagent
Result: silver precipitate (known as silver mirror) formed on sides of test tube
Reaction: oxidation (carboxylic acid produced)

Option 3:
Test: acidified dichromate
Result: colour of solution changes from orange -> green
Reaction: oxidation (carboxylic acid produced)

Question 11

Testing for ketones

Answer 11

NO TEST because ketones cannot be oxidised further

Question 12

Testing for carboxylic acids

Answer 12

Test: solid sodium carbonate or sodium hydrogen carbonate
Result: solid disappears; bubbles of CO2 evolved (effervescence); CO2 turns colourless limewater cloudy
Reaction: neutralisation