Module 6 Identifying aldehydes and ketones
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17 Terms
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