test substance may be solid or liquid, place on white tile and add IODINE SOLUTION (yellow orange colour)
POSITIVE RESULT = BLUE/BLACK COLOUR
NEGATIVE RESULT = NO COLOUR CHANGE - REMAINS YELLOW/ORANGE
Iodine bind to centre of AMYLOSE HELIX, changing colour from YELLOW to BLUE/BLACK.
1 of 5
test for REDUCING SUGARS
BENEDICT'S TEST for REDUCING SUGARS
solution placed in test tube, then same amount of BENEDICT"S SOLUTION added
HEAT to 80*c in water bath
POSITIVE RESULT - COLOURCHANGE from BLUE to GREEN then YELLOW/ORANGE then RED PRECIPITATE
FINAL COLOUR depends on concentration of reducing sugar - LOW = GREEN
NEGATIVE RESULT - NO CHANGE - REMAINS BLUE
MOST SUGARS REDUCING SUGARS - NOT SUCROSE
when mixed with oxidising agent & heated = redox reaction. Benedict's contains copper sulphate with copper ions, when react ions change to Cu+ to form red precipitate.
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test for PROTEINS
BIURET TEST FOR PROTEINS
solution in test tube, add equal amount of BIURET SOLUTION (copper sulFate & sodium hydroxide) & mix
POSITIVE RESULT - VIOLET/PURPLE COLOUR
NEGATIVE RESULT - NO CHANGE - BLUE OF COPPER SULFATE
3 of 5
test for LIPIDS
ETHANOL EMULSION TEST FOR LIPIDS
crush material in ethanol in test tube, filter into a 2nd test tube with cold water, discard solid residue DONT MIX
POSITIVE RESULT - MILKY EMULSION INDICATES LIPID.
4 of 5
test for NON REDUCING SUGARS
SUCROSE ONLY COMMON NON REDUCING SUGAR
if NEGATIVE RESULT WITH BENEDICT'S TEST:
add dilute hydrochloric acid & boil in water bath (acid=catalyst) cool test tube, add alkali then redo BENEDICTS TEST
POSITIVE = NON REDUCING SUGARS (PROBS SUCROSE) PRESENT IN ORIGINAL TEST SUBSTANCE, BUT NO REDUCING SUGARS
NEGATIVE = NO COLOUR CHANGE- NO NON REDUCING & NO REDUCING SUGARS.
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