Organic Analysis Flashcards
Give a test that can be used to identify an aldehyde?
- use Tollen’s reagent, and warm gently
- if an aldehyde is present, silver mirror will form
Give a test to identify the presence of primary and secondary alcohols
- add acidified potassium dichromate
- turns from orange to green if present
Why will tertiary alcohols not turn orange in the presence of potassium dichromate?
As it is not able to be oxidised
What does Fehling’s reagent test for? How is it carried out?
- the presence of aldehydes
- add Fehling’s reagent and warm gently
- if present, solution will turn from blue to brick red
What is a test for alkenes?
- add bromine water
- if present, orange turns to colourless
What is a test for a carboxylic acid?
- add sodium carbonate
- CO2 is produced
- gas is collected and tested with lime water
- will turn cloudy if CO2 (positive for COOH)
How does IR radiation show the functional groups present in a compound?
- IR radiation is passed through a sample
- different types of bond absorb different amounts of IR radiation
- these varying amounts of absorbance are measured and recorded and allow for certain bonds/functional groups to be identified
How is the test for an aldehyde carried out using Tollens’ reagent?
- Mix aqueous silver nitrate with aqueous sodium hydroxide.
- add concentrated ammonia solution until ppt. dissolves
- add few drops of solution, heat
- silver mirror will form
Describe the test and positive result for a haloalkane
warm with silver nitrate solution in ethanol
Cl- white ppt
Br- cream ppt
I- yellow ppt
Describe a test for any alcohol
add Mg, effervescence will form
Why do aldehydes give a positive result for Tollens’? For Fehling’s?
- as the reduce Ag+ to Ag, as they themselves are oxidised
- Cu2+ is reduced to Cu+, aldehydes are oxidised
