Tests for substances

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  • Created by: avbuck
  • Created on: 06-01-14 16:27
What is the test for the presence of sugars? (Hard)
Benedicts reagent
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Give an example of a reducing sugar.
Glucose
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What is the test for the presence of a reducing sugar?
1. Add an equal volume of blue benedicts reagent to the solution being tested. 2. Heat in a boiling water bath.
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What is the colour of the solution if a reducing sugar is present?
Gradually turns from blue to green to yellow to orange then red precipitate forms.
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Give an example of a non-reducing sugar.
Sucrose.
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What is the test for the presence of a non-reducing sugar?
1. Break the non-reducing sugar down into its monosaccharides by heating with HCl. 2. Benedicts reagent needs alkaline conditions so neutralise the solution by slowing adding alkali until any fizzing stops. 3. Add benedicts reagent. 4. Heat as before
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What is the colour of the solution if a non-reducing sugar is present?
Solution will turn from blue to red.
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Why is it possible to estimate the approximate level of a reducing sugar in a sample?
Because the benedicts test is a qualitative and semi-quantative test (getting approx. quantity of a sub) The diagram (pg11) shows the relationship between the concentration of a reducing sugar and the colour of the solution and precipitate formed.
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What is the test for starch?
Add orange-brown iodine solution. (typical)
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What is the colour of the solution if starch is present?
Goes from orange-brown to a blue-black colour.
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What is the test for proteins?
The biuret test. Add a few drops of biuret reagent.
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What is the colour of the solution if protein is present?
If no protein is present, the solution remains blue. If protein is present, a purple colour is formed.
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Other cards in this set

Card 2

Front

Give an example of a reducing sugar.

Back

Glucose

Card 3

Front

What is the test for the presence of a reducing sugar?

Back

Preview of the front of card 3

Card 4

Front

What is the colour of the solution if a reducing sugar is present?

Back

Preview of the front of card 4

Card 5

Front

Give an example of a non-reducing sugar.

Back

Preview of the front of card 5
View more cards

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