RP food tests

Question 1

equipment list

Answer 1

-food sample
-test tube
-water bath
-thermometer
-pipettes
-benedict’s solution
-iodine solution
-ethanol/sudan III solution
-distilled water
-biuret reagent
-measuring cylinder

Question 2

method (starch)

Answer 2

1. put 5cm³ of the food sample in a test tube
2. add a few drops of the iodine solution to the sample using a pipette and gently shake
3. if starch is present, the solution turns from brown/orange to blue/black

Question 3

method (reducing sugars)

Answer 3

1. add 5cm³ of the food sample to a test tube
2. add a few drops of benedict’s solution
3. place in a hot water bath at (80°C) for about 5 minutes
4. if reducing sugars are present, the solution will change from blue to green, yellow or brick-red

Question 4

what does the colour change for sugars depend on?

Answer 4

the amount of sugar in the food

Question 5

method (preparing sample)

Answer 5

1. grind a piece of food using a pestle and mortar
2. transfer to a beaker and add some distilled water
3. stir the mixture
4. filter using a funnel lined with filter paper

Question 6

method (protein)

Answer 6

1. add the sample to a test tube
2. add 2cm³ of biuret reagent and gently shake
3. if protein is present, the solution will change from blue to purple

Question 7

method (lipids sudan III)

Answer 7

1. add food sample to test tube
2. add a few drops of sudan III solution and gently shake
3. if the sample contains lipids, the mixture will separate into two layers and the top layer will be bright red

Question 8

method (lipids ethanol)

Answer 8

1. put some of the food sample in a test tube
2. add a few drops of distilled water
3. add a few drops of ethanol and gently shake
4. if lipids are present, a white emulsion is formed on the surface

Question 9

list the colour changes & reagents

Answer 9

protein-biuret, blue to purple
sugars-benedict’s, blue to green/yellow/brick red
starch-iodine, orange to blue/black
lipids-sudan III/ethanol, red layer/white emulsion

Question 10

risks

Answer 10

1. tie hair back, googgles
2. handle biuret with care (copper sulfate-poisonous, sodium hydroxide-corrosive)
3. keep ethanol/Sudan III away from flames as flammable
4. iodine is irritant

Question 11

what is biuret reagent made from?

Answer 11

potassium hydroxide and copper (II) sulfate