CHROMATOGRAPHY AND SPECTROSCOPY Flashcards
Test for alkenes
React with bromine water and shake
bromine water will go colourless as addition takes place
Test and further test for haloalkanes
Add dilute nitric acid to react with other anions other than halides to prevent false positive results
add silver nitrate
colour of precipitate shows which halide ion is present
AgCl - white precipitate
AgBr - cream precipitate
AgI - yellow precipitate
FURTHER TEST BY ADDING AMMONIA
Dilute ammonia dissolves AgCl
Conc ammonia dissolves AgBr
AgI is insoluble in ammonia
first test for phenols
Phenols react with strong bases
if phenol is present solid dissolves to form a colourless salt
If phenol is absent no visible reaction occurs
Second test for phenols
Test the sample with a weaker base such as a carbonate
carbonates only react with strong acids so wont react with phenol
effervescence seen when phenol not present
Test for carboxylic acids
React with a carbonate to produce carbon dioxide and water
(Sodium Carbonate solid or solution)
when CO2 bubbled through limewater it turns cloudy
Testing for carbonyl group
2,4 DNP dissolved in Conc H2SO4 and methanol and added to sample
if ketone or aldehyde is present a bright orange precipitate is observed
precipitate melting point can be compared with a known library so can help identify which aldehyde or ketone was in sample
How to distinguish between aldehyde and ketone and how is reagent made
tollens reagent is made by adding
- NaOH to silver nitrate (pale brown precipitate)
- add few drops of ammonia until precipitate dissolves
add aldehyde/ketone to tollens reagent and place in hot water bath
if aldehyde is present, tollens reduced to silver which coats test tube, silvery mirror
How to test for different types of alcohols
acidified K2CR2O7 oxidises primary and secondary but not tertiary alcohols
this is reduced from orange to green,
primary and secondary alcohols show same colour change, so distil products and test for aldehyde or ketone
What is mobile phase in TLC
a liquid solvent
What is stationary phase in TLC
silicon dioxide or aluminium oxide
Steps of TLC
