Test Method Positive Test Results Extra
Primary, Secondary, and tertiary Alcohols 1)      Add potassium dichromate solution

 

·        Primary and secondary alcohols can be oxidised by the Cr2O72-

·        Dichromate ions (Cr2O2-) are orange. On reduction Cr 3+ ions are formed which are green.

·        Primary + secondary remain green

·        Tertiary changes to orange

 

·        Primary alcohols are oxidised to aldehydes and the carboxylic acids

·        Secondary alcohols are oxidised to ketones.

·        Tertiary alcohols cannot be oxidised by the dichromate ions.

 

Primary and Secondary alcohols Using Tollens’ reagent

1)      diamminesilver(I) ion, [Ag(NH3)2]+ (containing silver(i) ions) is added

2)      drop of NaOH gives a precipitate of silver(i) oxide ions

3)      Add dilute NH3 to redissolve precipitate

4)      Few drops of aldehyde (primary) or ketone (secondary) is added

5)      Solution warmed gently in hot water bath for several minutes

·        Aldehyde (primary alcohol): Colourless solution producing silver mirror

·        Ketone (secondary alcohol): No change in the colourless solution

·        Large enough of aldehyde (from oxidation of primary alcohol) or ketone (from secondary alcohol) to be able to test them.
Carbocyclic Acids 1)      Add Sodium hydrogen carbonate

2)      Add limewater

·        Carbon Dioxide gas produced

·        Limewater turns cloudy

Halogenoalkanes 1)      Add Aqueous NaOH

2)      Warm the solution

3)      Acidify with nitric acid

4)      Add aqueous silver nitrate

·        Precipitate of silver halides formed
Alkenes 1)      Mix with bromine water ·        Solution changes from orange to colourless
Aldehyde and Ketones Using Tollens’ reagent

1)      diamminesilver(I) ion, [Ag(NH3)2]+ (containing silver(i) ions) is added

2)      drop of NaOH gives a precipitate of silver(i) oxide ions

3)      Add dilute NH3 to redissolve precipitate

4)      Few drops of aldehyde or ketone is added

5)      Solution warmed gently in hot water bath for several minutes

 

Fehling’s solution or Benedict’s solution

·        Both contain complexed copper(II) ions in an alkaline solution.

·        Fehling’s solution contains copper(II) ions complexed with tartrate ions in sodium hydroxide solution

·        Benedict’s solution contains copper(II) ions complexed with citrate ions in sodium carbonate solution.

1)      A few drops of the aldehyde or ketone are added to the reagent

2)      Mixture is warmed gently in a hot water bath for a few minutes.

 

 

·        Aldehyde: Colourless solution producing silver mirror

·        Ketone: No change in the colourless solution

 

 

 

 

 

 

 

·        Aldehyde: Blue solution -> Dark red ppt (Cu2O ppt)

·        Ketone: No change (blue solution)

 

Metal Halides 1)      Add dilute nitric acid

2)      Add a few drops of silver nitrate

·        Fluoride = no precipitate

·        Chloride = White precipitate (able to dissolve in dil. NH3)

·        Bromide = Cream precipitate (able to dissolve in conc. NH3)

·        Iodide = Yellow precipitate

(insoluble)