Test For Organic functional groups Flashcards
What is bromine water used to test for?
Alkenes, it tests for a double bond (unsaturated means double bonds)
Alkene the solution becomes colour less
Not alkene, nothing happens
Add 2cm^3 of substance add 2cm^3 of bromine water and then shake the tube
What is AgNO3 (silver nitrate) used to test for?
A few things:
Chloroalkane - White PPT
Bromoalkane - Pale cream PPT
Iodoalkane - pale yellow PPT
Add substance to test tube add 1cm^3 of ethanol and AgNO3 and place in a warm water bath
What can sodium hydroxide and a carbonate test for?
Phenols!
You are testing the weak acid nature as it is tricky.
NaOH is a strong base and will react with any acid. Add 2cm^3 of substance then add a small spatula of NaOH solid.
If phenol or acid the solid will dissolve and form a colourless solution of a sodium salt.
Next you need to test with carbonate
2cm^3 of unknown substance then a small spatula of solid carbonate or 2cm^3 of carbonate solution like sodium carbonate.
If it is a phenol nothing will happen
If is is a strong acid it will fizz and bubble
What can sodium carbonate be used to test for?
carboxylic acids
The carboxylic acid will react with the carbonates to form a salt and CO2 and H2O
Add 2cm^3 of substance to be measured
Add one small spatula of solid carbonate or 2cm^3 of sodium carbonate
A carboxylic acid will fizz and the gas will turn limewater cloudy
If it is not a carboxylic acid nothing will happen
How to test for a Carbonyl group?
Using 2,4-DNP this tests for aldehydes and ketones
Dissolve 0.2g of 2,4-DNP into 1cm^3 of sulphuric acid, 2cm^3 of water and 5cm^3 of methanol (this solution is Brady’s reagent)
In a different test tube add 5 drops of unknown substance to 2cm^3 of your solution
Shake the tube
Aldehyde/ketone = bright orange PPT
Not Aldehyde or ketone = nothing happens
What dose Tollens’ reagent test for?
Aldehydes
Put 2cm^3 of 0.1 concentration AgNO3 in a test tube, add 5 drops of 0.8 concentration NaOH (brown PPT forms)
Add drops of dilute ammonia solution until the brown ppt dissolves, put test tube in hot water and add 10 drops of substance
If:
Aldehyde = silver mirror will form
Not aldehyde = nothing will happen
What is acidified dichromate used to test for?
Primary and secondary alcohols
Add 10 drops of alcohol to 2cm^3 of acidified potasium dichromate into a test tube
Warm the mixture in a hot water bath
Watch for a colour change if:
Primary = orange solution will turn green as aldehyde forms
Secondary = orange solution will turn green as ketone is formed
Tertiary = nothing happens
