Identification of organic molecules Flashcards
How do you test for an alkene?
Add bromine water
What is the positive result for testing for alkenes with bromine water?
The bromine water goes colourless
How do you test for a carbonyl?
Add 2,4-DNPH (Brady’s)
What is the positive result for testing for a carbonyl with Brady’s?
Yellow/orange precipitate
How do you use Brady’s to identify individual carbonyl compounds?
The compounds formed from this reaction, known as derivatives, can be filtered, purified and dried, and their melting point measured.
This melting point can then be matched to the recorded data book value of a certain carbonyl.
What 3 reagents can be used to oxidise aldehydes but not ketones?
Fehling’s solution
Benedict’s solution
Tollen’s reagent
What is the positive colour change for oxidisation with Fehling’s solution and Benedict’s solution?
If an aldehyde is present, it will change from a blue solution to a red precipitate
What is the positive colour change for oxidisation with Tollen’s reagent?
If an aldehyde is present, it will change from a colourless solution to a silver mirror
What will acidified potassium dichromate oxidise?
Primary alcohols, secondary alcohols and aldehydes
What is the colour change for oxidation with acidified potassium dichromate?
Orange to green
What causes the colour change in oxidation with acidified potassium dichromate?
Reduction of dichromate ions
What causes the colour change in oxidation with Fehling’s and Benedict’s?
Conversion of a copper (II) complex to copper (I) oxide
What causes the colour change in oxidation with Tollen’s?
Conversion of silver complex to metallic silver
What is Tollen’s also known as?
Ammoniacal silver nitrate
What does the iodoform reaction test for?
Carbonyls with a CH3CO group, and alcohol precursors
What aldehydes will give a positive iodoform test?
Only ethanal
What ketones will give a positive iodoform test?
All ketones with the carbonyl group on the second carbon (methyl ketones)
What alcohols will give a positive iodoform test?
As oxidising conditions are used, all alcohols that can be oxidised to ethanal or a methyl ketone will give a positive result
What is the positive result for the iodoform test?
Pale yellow precipitate
How do you test for a carboxylic acid?
Add sodium carbonate
What is the positive result for testing for carboxylic acids with sodium carbonate?
Evolution of carbon dioxide
How do you test for acyl chlorides?
Add water
What is the positive result for testing for acyl chlorides with water?
Evolution of hydrogen chloride
How do you test for phenols or phenylamines?
Add bromine water
What is the positive result for testing for phenols and phenylamines with bromine water?
Bromine water colour disappears and white precipitate forms
How do you test for just phenols?
Add to sodium carbonate solution
What is the positive result for testing for phenols using a sodium carbonate solution?
Phenol will dissolve without the evolution of carbon dioxide
How do you test for carbon dioxide?
Bubble with limewater (aqueous calcium hydroxide)
What is the positive result for testing for CO2 with limewater?
Solution goes cloudy and a white precipitate forms
How do you test for H2?
Squeaky pop test- put a lit splint near the products
