Tests for functional groups

Question 1

How do you test for halide ions ?

Answer 1

Dissolve the sample in dilute nitric acid and add silver nitrate solution
Then add dilute/concentrated ammonia solution
Observations
White ppt = chloride
Cream ppt = bromide
Yellow ppt = iodide
No ppt = none

Question 2

How do you test for sulfate ions ?

Answer 2

Dissolve the sample in dilute nitric acid or HCl and add Barium chloride solution
Observation:
White ppt = Sulfate ions are present (SO4^2-)
No ppt = no Sulfate ions

Question 3

How do you test for aldehydes ?

Answer 3

Tollen’s reagent-silver mirror forms
Fehling’s/ Benedicts reagent - Blie to brick red ppt
Acidified potassium dichromate - orange to green (also positive for alcohols)

Question 4

How do you test for alkenes ?

Answer 4

Bromine water - orange to colourless

Potassium manganate - kMnO4 - “decolourises” - purple to brown

Question 5

How do you test for alcohols ?

Answer 5

Acidified:
Potassium dichromate-orange to green
Potassium manganate- purple to colourless

(Tertiary alcohols are hard to oxidise)

Question 6

How do you test for carboxylic acids ?

Answer 6

Sodium (hydrogen) carbonate - effervescence

Question 7

how would you identify between a carboxylic acid and an alcohol ?

Answer 7

sodium hydrogen carbonate is positive for carboxylic acids producing effervescence
acidified potassium dichromate is positive for alcohols, orange to green