Biochemical Tests

Notes on the biochemical tests for AS Biology x

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Natasha Naeem 12DJH
Chemical Compound Test Positive Result Negative Result
Starch Add a few drops of A blue-black colour No colour change.
iodine/potassium iodide change. Indicates Stays an
solution to the sample. the presence of orange/brown
starch as a yellow.
complex is formed.
Reducing Sugars Add a few mL of A coloured No colour change.
Benedict's reagent to the precipitate is Stays a pale blue
sample. Shake and heat formed. Indicates colour.
for a few minutes at 95°C the presence of a
in a water bath. reducing sugar. A
green precipitate
means relatively
little sugar, a brown
or red precipitate
progressively more
sugar is present.
Non-reducing Sugars Test a sample for reducing A coloured No colour change.
sugars, to see if there are precipitate is Stays a pale blue
any present before formed. A green colour.
hydrolysis. Then, using a precipitate means
separate sample, boil the relatively little
test solution with dilute sugar, a brown or
hydrochloric acid for a few red precipitate
minutes. Neutralise the means
solution by gently adding progressively more
small amounts of solid sugar is present.
sodium hydrogen
carbonate until it stops
fizzing, and then test for
reducing sugars again.
Lipids Vigorously shake some of The lipids will No colour change.
the test sample with 4 mL precipitate in the Remains clear.
of ethanol. Decant the water, forming a
liquid into a second test cloudy white
tube of water, leaving any emulsion.
undissolved substances
Protein Add a few mL of biuret The solution will No colour change.
solution to the sample. turn a lilac purple Stays a blue colour.
Shake. colour.
Biochemical Tests



this was really useful, thanks:)

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