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Unit 2.1.1. OCR
Biochemical Tests For Molecules
Benedict's Test for Sugars
Sugar Monosaccharides + disaccharides.
Classified as reducing or non-reducing.
Test for sugars Benedict's Test
All Monosaccharides (e.g. glucose) + some disaccharides (e.g.
1. Add Benedict's reagent (blue) to a sample.
2. Heat but don't boil.
Positive form a coloured precipitate (solid particles suspended n the
Blue to green to yellow to orange to brick red
The higher the concentration, the further along the colour changes.
This can show the amount of reducing sugar in a solution.
More accurate filter solution + weigh precipitate.
To test for a N-RS, E.g. sucrose, they have to be broken down into
1. Carry out the reducing sugar test if negative use this test.
2. Boil solution with dilute hydrochloric acid.
3. Neutralise with sodium hydrogencarbonate.
4. Carry out Benedict's test for reducing sugars again.
5. If positive form a coloured precipitate.
Iodine Test for Starch
NOTE: always say "iodine in potassium iodine solution" not just "iodine".
Add iodine dissolved in potassium iodine solution to sample.
Starch Present Colour change from browny-orange to blue-black.
No Starch Stays browny-orange.
Biuret Test for Proteins
1. Add sodium hydroxide solution turns alkaline.
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Unit 2.1.1. OCR
2. Add copper(II) sulfate solution.
Protein Present purple layer forms.
No Protein Stays blue
Emulsion Test for Lipids
1. Add ethanol.
3. Pour into water.
Lipid present turns milky the more lipid, the more noticeable.
No lipid solution stays clear.
A machine used to determine the concentration of a glucose
Measures strength of a coloured solution - sees how much light
passes through it.…read more