Identification of Organic groups

Question 1

How can you identify an Alkene group?

Answer 1

React with bromine water - decolourises if a C=C bond is present.
Remains orange if not.

Question 2

How can you identify a Halogenoalkane group?

Answer 2

React with Silver nitrate.
Cl - White ppt
Br - cream ppt
I - Yellow ppt

Add Ammonia to make distinguishing between Cl and Br easier, Cl ppt will dissolve quicker.

Question 3

How can you identify Alcohol groups?

Answer 3

React with acidified Potassium dichromate - Coour change from orange to green in the prescence of Primary or Secondary alcohols

Question 4

How can you identify an Aldehyde group?

Answer 4

Silver mirror with Tollen’s reagent
Brick red ppt with Fehling’s solution
Acidified potassium dichromate makes the solution go green

Question 5

How can you identify a Ketone group?

Answer 5

Positive test result with acidified potassium dichromate - means either aldehyde or ketone
Negative result on Tollen’s or Fehling;s means Ketone

Question 6

How can you identify an Carboxylic acid?

Answer 6

pH will be less than 7
React with a carbonate - effervescence & CO₂ will be formed. Bubble gas produced through limewater, cloudy limewater indicates positive result

Question 7

How can you indentify an Ester group?

Answer 7

They have distinct sweet smells