Food Tests OCR Unit 2 Module 1

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What is the test for starch?
Add a solution of Iodine to the sample.
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What is a positive test for Starch?
If the Iodine solution changes colour from yellow-brown to blue-black.
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What does the term 'reducing sugar' mean?
The molecule can react with other molecules by giving electrons to them.
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How do you test for reducing sugar and what is a postive test?
Heat with benedict's solution. The solution will change colour from blue to an orange-red precipitate will form if positive.
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How do you test for non-reducing sugars?
1. Make sure there are no reducing sugars (benedicts solution), 2. Boil sample with HCl, 3. This hydrolyses any sucrose present, splitting sucrose to give glucose and fructose, 4. Cool the solution and neutralise it, 5. Carry out reducing sugars test
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How do you test for Protein and what is a postive result?
Add biurets reagent to a sample. Biurets is blue and contains sodium hydroxide and copper sulphate. These chemicals react with the peptide bonds in proteins causing a colour change from blue to lilac.
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How do you test for the presence of lipids and what is a positive result?
Test using the ethanol emulsion test - mix samples with ethanol which dissolves any lipid present, pour the liquid (alcohol and dissolved fat) into water in clean test tube. If a lipid is present a cloudy white emulsion will form near the top.
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What is meant by chemical reduction?
Adding electrons to another molecule or particle. (gain of electrons)
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Why would a solution of amino acids give a negative test with biurets reagent?
They have no peptide bonds so there will be no colour change.
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What is a precipitate?
When a substance comes out of solution and forms solid particles dispersed in the solution.
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Other cards in this set

Card 2

Front

What is a positive test for Starch?

Back

If the Iodine solution changes colour from yellow-brown to blue-black.

Card 3

Front

What does the term 'reducing sugar' mean?

Back

Preview of the front of card 3

Card 4

Front

How do you test for reducing sugar and what is a postive test?

Back

Preview of the front of card 4

Card 5

Front

How do you test for non-reducing sugars?

Back

Preview of the front of card 5
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