tests for aldehydes

Question 1

what are the tests for aldehydes

Answer 1

silver mirror test
fehlings
acidified potassium permanganate

Question 2

method for fehlings test

Answer 2

add equal parts fehlings 1 and 2 in a test tube
note and record colour
add a few drops of ethanal
place in beaker of hot water
record colour change

Question 3

what colour change is observed in fehlings

Answer 3

royal blue to prick red precipitate

Question 4

explain the colour change of fehlings

Answer 4

royal blue to brick red precipitate

Cu2+ —> Cu+
reduced

ethanal oxidised to ethanoic acid

Question 5

explain the method of acidified potassium permanganate aldehyde test

Answer 5

1/4 fill a test tube with KmNO4/H+
add a few drops of ethanal
place test tube in a beaker of hot water
record colour change

Question 6

explain the method of the silver mirror test

Answer 6

mix silver nitrate
dilute ammonia
dilute NaOH
add a few drops of ethanal
place test tube in hot breaker
record colour change

Question 7

mnemonic device for silver mirror test reagents

Answer 7

silly nuns drink silly hot alcohol
silver nitrate
dilute sodium hydroxide
ammonia

Question 8

colour change of the silver mirror test

Answer 8

colourless —> silver precipitate

Question 9

colour change of KmNO4 test for aldehydes

Answer 9

purple —> colourlesss

Question 10

explain the colour change of the silver mirror test

Answer 10

colourless —> silver precipitate

Ag+ reduced to Ag

Question 11

explain the colour change for KmNO4/H+

Answer 11

Purple –> colourless

Mn7+ reduced to Mn2+