Carbonyl Compounds

Question 1

Test for carbonyl compounds

Answer 1

Brady’s reagent / 2,4- dinitrophenylhydrazine ( 2.4-DNPH)

• add a few drops of the unknown sample to 5 cm3 of brady’s reagent
• the presence of a carbonyl compound is indicated by a yellow / orange precipitate

Question 2

How can you test for an aldehyde using fehlings solution

Answer 2

• warm the sample with fehling’s solution

- if an aldehyde is present, the blue solution will form a brick red precipitate

Question 3

How can you test for an aldehyde using tollen’s reagent

Answer 3

• Add tollen’s reagent to the sample and warm in a water bath
• the presence of a silver mirror on the test tube indicates that the sample contains an aldehyde functional group

Question 4

How do ch 3 co - compounds react with alkaline aqueous iodine? (Triodomethane test)

Answer 4

• Iodine is added to the aldehyde or ketone solution
• just enough na oh is added until the iodine is decolorised
• a pale yellow precipitate of triodomethane chi3 is formed