Identification of Functional Groups by Test-Tube Reactions

Question 1

Some simple questions which can be considered are:
Is the compound acidic?
If so, it could be a carboxylic acid
What state is the compound in?

Answer 1

If solid, it could suggest long C-C chains or strong intermolecular forces

If liquid, it could suggest medium C-C chain length, or something polar

If gas, it will likely have very short C-C chain length and is unlikely to be polar

Question 2

Is it soluble in water?

Answer 2

If so, then it suggests that the compound has polar groups and if not, then it suggests that it does not have polar groups present

Question 3

Following this, simple chemical tests can also be done, to determine the functional groups which are present
These are known as

Answer 3

test-tube reactions

Question 4

alkene test

Answer 4

shake with bromine water

turns from orange to colourless

Question 5

halogenoalkane

Answer 5

add aqueous sodium hydroxide and warm gently

acidify with nitric acid (HNO3)

add silver nitrate

AgCl-white
AgBr-cream
AgI- pale yellow

Question 6

alcohol test r- OH

Answer 6

add acidified potassium dichromate solution

orange turns to green with primary and secondary alcohols

no reaction with tertiary

Question 7

Aldehydes R- CHO

Answer 7

Warm with tollens reagent and Fehlings

silver mirror forms

blue solution to red precipitate

Question 8

carboxylic acid

R-COOH

Answer 8

add sodium hydrogen carbonate (NaHCO3

co2 gas is formed