Test for functional groups Flashcards
Why do we need to carry out tests
To be able to distinguish between chemicals
Describe the test between primary, tertiary and secondary alcohols
> Oxidize alcohols using acidified potassium dichromate
Add 10 drops of the alcohol to 2cm3 of the chromate
Warm the mixture in a water bath
Primary and secondary alcohols will turn from orange to green while tertiary alcohols will remain orange/no reaction
Give another test for alcohols
> Sodium metal
Add a small piece of sodium to a pure alcohol and it will fizz as it gives off hydrogen gas
Why does the chromium go from orange to green?
Because its being reduced
How do you test for primary and secondary alcohols
> Fractional distillation setup
Distill an alcohol, if an primary alcohol, it will produce an aldehyde which will turn brick red in Fehling’s
and benedicts solution
Distill an alcohol, if an secondary alcohol, it will produce an Ketone, there will be no reaction in Fehling’s and benedicts solution
Or reflux both alcohols, if a primary alcohol, a carboxylic acid is formed which fizz, or form an effervescence in sodium carbonate
Describe the test for a carboxylic acid
> Add sodium carbonate to 2cm3 of carboxylic acid which will fizz and produce co2.
Bubble through limewater to turn cloudy
describe the test for an aldehyde
> Tollens reagent, forms a silvery mirror
Fehling’s solution, turns from deep blue to brick red precipitate
Describe the test for ketones
> Tollens reagent, no reaction
Fehling’s solution, no reaction
Describe the test for halogenoalkanes
> Heat with aqueous sodium hydroxide
Then acidify with nitric acid then add silver nitrate solution
For chloride, a white precipitate is formed
For bromide, a cream precipitate is formed
For iodide a yellow precipitate is formed
Describe the test for alkenes
> Add 2cm3 of alkene and 2cm3 of bromine water and shake gently
Orange bromine water decolourises
