Tests for the presence of substances Flashcards

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1
Q

What is the method for testing for a non-reducing sugar?

A
  • Add HCl, boil and cool the solution
  • Add sodium hydrogencarbonate
  • Add Benedict’s reagent
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2
Q

What is observed in the Benedict’s test for a reducing sugar if a reducing sugar is not present?

A

Solution remains blue

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3
Q

What is observed in the Benedict’s test for a reducing sugar if a reducing sugar is present?

A

A red precipitate is formed

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4
Q

Why is acid used in the Benedict’s test for a non-reducing sugar?

A

It hydrolyses the glycosidic bond

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5
Q

Why is sodium hydrogencarbonate used in Benedict’s test for a non-reducing sugar?

A

Neutralises the solution as Benedict’s reagent doesn’t work in acidic conditions

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6
Q

What is the test used for a reducing sugar?

A

Add an equal amount of benedict’s solution

Place in a water bath for 3 minutes

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7
Q

What is observed in the Benedict’s test for a non-reducing sugar if a non-reducing sugar is present?

A

Brick red precipitate formed

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8
Q

How can starch be tested for?

A

Adding potassium iodide solution

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9
Q

What is observed in a positive starch test?

A

Black/dark purple solution is formed

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10
Q

Describe the method for testing for the presence of proteins

A

Add Biuret’s reagent down the side of the test tube

Shake

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11
Q

What is observed in a positive test for proteins?

A

Purple solution is formed

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12
Q

Describe the method for testing for lipids

A
  • Add ethanol and shake

- Add this solution to water and shake

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13
Q

What is observed in a positive test for lipids?

A

A white emulsion is formed

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