Module 6 Identifying aldehydes and ketones

what are the 3 types of reactants

tollens reagent, 2,4 DNP, Fehlings solution

what are the results for tollens reagent on aldehyde

precipitate of silver

what are the results for tollens reagent on ketone

no reaction

what is the 2,4 DNP test step 1

add 5cm of solution of 2,4-dinitrophenylhydrazine in excess to clean test tube

what is the 2,4 DNP test step 2

use dropping pipette and add 3 drops of unknown compound and leave to stand

what is the 2,4 DNP test step 3

if no crystals form, add few drops of sulfuric acid

what is the 2,4 DNP test step 4

yellow/orange precipitate indicates presence of aldehyde or ketone

who do you identify aldehyde or ketone by melting point

filter impure yellow/orange solid, recrystallise solid to produce pure sample of crystals, melting point of purified 2,4-dinitrophenylhydrazone is measured and recorded

what is reaction with fehlings solution step 1

use dropper pipette to place about 1cm3 fehlings solution A into test tube

what is reaction with fehlings solution step 2

add equal quantity of fehlings solution B and shake tube gently to mix the solutions

what is reaction with fehlings solution step 3

use dropper pipette to add 0.5cm3 of propanal to test tube

what is reaction with fehlings solution step 4

shake carefully to mix then warm tube and its contents in freshly boiled hot water in 250cm3 beaker

what is reaction with tollens reagent step 1

use dropper pipette to place 1cm3 of 0.1moldm-3 silver nitrate solution in test tube

what is reaction with tollens reagent step 2

use clean dropper pipette to add drop of dilute sodium hydroxide solution which should produce a brown precipitate

what is reaction with tollens reagent step 3

add dilute ammonia solution drop by drop until brown precipitate has dissolved. the colourless solution left is tollens reagent

what is reaction with tollens reagent step 4

use dropper pipette to add 0.5cm3 of propanal to test tube

what is reaction with tollens reagent step 5

shake carefully to mix then warm tube

other ways to identify aldehydes and ketones

by melting point

how to identify aldehydes or ketones by melting point

filter impure yellow/orange solid, recrystallise solid to produce pure sample of crystals, melting point of purified 2,4-dinitrophenylhydrazone is measured and recorded