Required Practical 3 - Uuse qualitative reagents to test for a range of carbohydrates, lipids and proteins.

Question 1

Food Tests Practical

Answer 1

• Take the food sample and grind with distilled water using a mortar and pestle
• Transfer the paste to a beaker and add more distilled water
• Stir the mixture so the food chemicals dissolve in the water
• Filter the solution to get rid of solid bits of food

Question 2

How do you test for carbohydrates / strach

Answer 2

Place 2cm3 of the food sample into the test tube and a few drops of iodine solution

Question 3

What colour will the iodine solution change into if starch is present

Answer 3

Browny-orange to blue-black

Question 4

How do you test for sugars

Answer 4

Place 2cm3 of the food sample into the test tube , then add 10 drops of benedict solution

Question 5

If sugars are present using benedicts’s solution, the mixture turns

Answer 5

Blue to green/Orange/brick red (depending on how much sugar )

Question 6

What does green solution mean when testing for sugar

Answer 6

There is a small amount of sugar

Question 7

What does yellow solution mean when testing for sugars

Answer 7

More sugar is present

Question 8

What does a brick red colour mean when testing for sugar

Answer 8

A lot of sugar is present

Question 9

What type of sugars work for the Benedict’s test

Answer 9

reducing sugars eg glucose

Question 10

How do you test for proteins

Answer 10

Place 2cm3 of the food sample into the test tube and add 2cm3 of biuret solution

Question 11

If protein is present what colour will the solution turn into from

Answer 11

Blue to purple

Question 12

How do you test for lipids?

Answer 12

Prepare 2cm3 of the food sample but you don’t need to filter it , then add a few drops of distilled water and ethanol

Question 13

If lipids are present what will happen to the solution?

Answer 13

A white cloudy emulsion will form

Question 14

What do you make sure of when testing with ethanol

Answer 14

No naked flames are present as ethanol is flammable

Question 15

Why don’t you filter the lipid sample like the rest

Answer 15

Lipid molecules can stick to filter paper

Question 16

Other way of testing for lipids

Answer 16

Prepare 2cm3 of food sample and add 3 drops of Sudan 111 stain solution

Question 17

How would you know if lipids are present (Sudan 111 solution)

Answer 17

The mixture will separate in. 2 layers and the top layer will be bright red