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 reagent in the test for starch?

Answer 2

Iodine

Question 3

What is the test for starch?

Answer 3

1. Add 2cm squared of the sample being tested into a test tube
2. Then add 2 drops of iodine solution and shake/stir
3. If starch is present, a colour change from yellow to blue-black should occur

Question 4

What temperature is this test conducted at?

Answer 4

Room temperature

Question 5

What is the reagent in the test for proteins?

Answer 5

Biuret

Question 6

What is the test for proteins?

Answer 6

1. Add protein sample being tested to test tube
2. Add biuret to protein sample and mix gently
3. If protein is present, a colour change form blue to purple will occur

Question 7

What will happen if proteins are absent from the sample?

Answer 7

If there are no proteins, the blue colour will remain

Question 8

What is the reagent for the test for lipids?

Answer 8

Ethanol

Question 9

What is the test for lipids?

Answer 9

1. Add 2cm cubed of the sample being tested and add 5cm cubed ethanol
2. Shake the tube thoroughly to dissolve any lipid in the sample
3. Add 5cm cubed of water and shake gently
4. If lipids are present a white, milky emulsion will form

Question 10

Why does a cloudy appearance in the test?

Answer 10

A cloudy colour appears because light appears through this emulsion is refracted as it passes from oil droplets to water droplets

Question 11

Why is there a cloudy colour?

Answer 11

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

Question 12

What is a reducing sugar?

Answer 12

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

Question 13

What is a reduction reaction?

Answer 13

A chemical reaction involving the gain of electrons or hydrogens

Question 14

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

Answer 14

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

Question 15

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

Answer 15

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

Question 16

What is a test for reducing sugars?

Answer 16

1. Grind up sample being tested, if not already liquid
2. Add 2cm cubed of the sample being tested to the 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 solution change from blue to brick red

Question 17

What are non - reducing sugars?

Answer 17

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

Question 18

What is an example of a non - reducing sugar?

Answer 18

Sucrose

Question 19

What is another reason non - reducing sugars are non - reducing?

Answer 19

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

Question 20

How do you detect a non - reducing sugar?

Answer 20

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

Question 21

What is the test for non - reducing sugar?

Answer 21

1. Grind sample up if not already liquid
2. Add 2cm cubed of sample and 2cm cubed of Benedict’s reagent to a test tube
3. Conduct Benedict’s test and after a negative result, add dilute hydrochloric acid
4. Heat test tube and bring to gentle boil
5. Allow solution to cool, then add sodium hydrogen - carbonate solution to neutralise the solution
6. Restest the solution by adding Benedict’s reagent and heat the solution
7. A positive test will show a solution colour change from blue to brick - red