Identification of Organic Molecules Flashcards
What is the first way of determining whether an organic substance is an alkene?
Add bromine water to the substance and it will turn from brown to colourless
What is the second way of determining whether an organic substance is an alkene?
Add acidified potassium manganate (purple) and shake which will decolourise the manganate as a diol is formed
How do you test for a carbonyl group?
Add small amount of 2,4-dinitrophenylhydrazine and a yellow/orange precipitate will slowly form
What is Brady’s reagent?
2,4-dinitrophenylhydrazine dissolved in methanol and conc sulfuric acid
What is the main difference between aldehydes and ketones?
Aldehydes are easily oxidised, whilst ketones aren’t
How do you make Tollens’ reagent?
Dissolve silver nitrate in aqueous ammonia
What happens when an aldehyde is heated in a test tube with Tollens’ reagent?
A silver mirror is formed
What is the ionic equation of the formation of a silver mirror?
Ag(NH3)2 + +e- —-> Ag +2NH3
What is Fehling’s solution?
A blue solution of complexed copper (2) ions dissolved in NaOH
What happens when Fehling’s solution is heated with an aldehyde?
The blue copper(2) ions are reduced to a brick-red precipitate of copper(1) oxide. Cu2+ +e- –> Cu+
What is Benedict’s solution?
The same as Fehling’s solution, however the copper (2) ions are dissolved in sodium carbonate instead of sodium hydroxide
What happens when Benedict’s solution is heated with an aldehyde?
The blue copper (2) ions are reduced to a brick-red precipitate of copper(1) oxide
What happens when you heat an aldehyde with acidified dichromate ions?
A carboxylic acid is formed
When an aldehyde is oxidised by acidified dichromate ions, what is the colour change of the dichromate ions?
Orange to green
If something contains a methyl carbonyl group, what must it be?
Either ethanal or a ketone with at least one methyl group
What happens when carbonyls which contain a methyl carbonyl group are heated with iodine in the presence of an alkali?
If there is a methyl carbonyl group a yellow precipitate of triidomethane will form and an antiseptic smell
How do you test for primary or secondary alcohols?
Warm with potassium dichromate and add dilute sulfuric acid and the substance will change from orange to green
How do you test for a carboxylic acid?
Add some sodium carbonate solution and carbon dioxide will be formed
How do you test for an acyl chloride?
Add substance to water and hydrogen chloride will be formed
What happens when phenol is added to sodium carbonate solution?
It dissolves without the evolution of carbon dioxide
What happens when you add phenol to water, shake and then add a few drops of iron chloride solution?
A purple colour is seen
What happens when you add phenol/phenylamine to brown bromine water and shake?
Bromine colour goes and white precipitate is formed
What is the colour of a dichromate ion?
Orange
