the tests of biological molecules (the emulsion test - for lipids (if you…
the tests of biological molecules
Benedicts test - for sugars
REDUCING SUGARS: add benedicts reagent to a sample adn then eat in a water bath until boiling.
POSITIVE: will form a coloured precipitate
NEGATIVE: will stay blue
NON- REDUCING SUGARS: break sample down into monosccharides. you have to get a new sample and add dilute hydrochloric acid. heat n water bath. finally, neutralise it with sodium hydrogencarbonate. carry out benedicts test.
POSITIVE: form coloured precipitate
NEGATIVE: with stay blue - sugar isnt present.
example of a non- reducing sugar is sucrose
the emulsion test - for lipids
if you want to find out if there is any fat in food you can use the emulsion test - this test is for LIPIDS
there are 3 steps: put test substance with ethanol in a test tube. shake for 2 minutes. pour into water.
POSITIVE: any lipids will show a milky white colour.
the biuret test - for proteins
two steps: you add sodium hydroxide solution. you then add copper sulfate solution.
protein is present if it turns PURPLE
no protein if it stays blue.
the iodine test for starch
add iodine dissolved in potassium iodide solution to the test sample.
POSITIVE: changes from browny-orange to dark blue-black.