Biochemical Tests

Question 1

What is a reagent?

Answer 1

A compound/mixture added to a system to start or test a chemical reaction

Question 2

What is the test for starch?

Answer 2

1. Place sample of starch into test tube
2. Then add two drops of iodine solution
3. Stir
4. If starch is present, a colour change from orange to blue/black should occur

Question 3

What is the reagent in the test for starch?

Answer 3

Iodine

Question 4

What temperature should the test for starch be?

Answer 4

Room temperature

Question 5

What will happen if proteins are absent from the sample?

Answer 5

If there are no proteins, the colour will remain blue

Question 5

What is the reagent for the test for proteins?

Answer 5

Biuret

Question 6

What is the test for proteins?

Answer 6

1. Add sample of protein to test tube
2. Add biuret to protein sample and mix
3. If protein is present, a colour change from blue to purple wil occur

Question 7

What is the reagent for the test for lipids?

Answer 7

Ethanol

Question 8

What is the test for lipids?

Answer 8

1. Add lipid sample and ethanol to test ube
2. Shake the tube thoroughly to dissolve and lipid in the sample
3. Add water and shake gently again
4. If lipids are present, a white milky emulsion will form

Question 9

Why is there a cloudy appearance in the test?

Answer 9

A cloudy appearance occurs because the light shown through this emulsion is refracted as it passees from oil droplets to water droplets

Question 10

What is a reduction reaction?

Answer 10

A chemical reaction involving the gain of electrons or hydrogens

Question 10

Why is there a cloudy appearance?

Answer 10

The cloudy appearance is due to the lipid in the sample being finely dispersed in the water to form an emulsion

Question 10

What is a reducing sugar?

Answer 10

A sugar that can donate electrons to (or reduce) another chemical

Question 11

What show a higher concentration of reducing sugar in a test for reducing sugars?

Answer 11

If the solution is more red, like the colour of red is deep or darker, there is a higher concentration of reducing sugars

Question 11

What happens when a reducing sugar is heated with Benedict’s reagent?

Answer 11

When a reducing sugar is heated with Benedict’s reagent it forms an insoluble red precipate of copper oxide

Question 12

What is the test for reducing sugars?

Answer 12

1. Grind up sample being tested, if not already liquid
2. Add sample of reducing sugar to test tube
3. Add equal volume of Benedict’s reagent
4. Heat the mixture to a gentle boil
5. A positive test should show a soluti

Question 13

What are non - reducing sugars?

Answer 13

A sugar that serves as a reducing agent due to its free aldehyde or ketone functional groups in its molecular structure

Question 14

What is an example of non - reducing sugars?

Answer 14

Sucrose

Question 15

What is another reason non - reducing sugars are non - reducing? (colour)

Answer 15

This is because they do not change the colour of Benedict’s reagent when heated

Question 16

How do you detect a non - reducing sugar?

Answer 16

To detect a non - reducing sugar, it must be hydrolysed into its monosaccharide components

Question 17

What is the test for non - reducing sugars?

Answer 17

1. Grind up the sugar sample if not already liquid​
2. Add liquidated sample and Benedict’s reagent to a test tube​
3. Conduct Benedict’s test, once you receive a negative result, add dilute hydrochloric acid ​
4. Heat test tube and bring to a gentle boil​
5. Allow solution to cool, then add sodium hydrogen carbonate sodium to neutralise the solution​
6. Retest the solution by adding Benedict’s reagent and heat the solution​
7. A positive test should show show a colour change from blue to brick red