Biochemical Tests

Question 1

What are qualitative and quantitative measures? (2)

Answer 1

• Qualitative - observable characteristics e.g. colour, gender, race
• Quantitative - Numerical measurements e.g. length, mass, force

Question 2

What two things do you need to test for in carbohydrates? (2)

Answer 2

• Starch
• Sugars (reducing and non-reducing)

Question 3

How do you test for starch? (1)

Answer 3

• Add iodine to the sample

Question 4

If starch is present what will be the colour change? (1)

Answer 4

Yellow/brown to blue/black

Question 5

Is testing for starch a qualitative or quantitative measure? (1)

Answer 5

Qualitative because you only observe if there is a colour change

Question 6

Examples of reducing sugars (2)

Answer 6

• All monosaccharides
• Some disaccharides (maltose and lactose)

Question 7

How do you test for reducing sugars? (2)

Answer 7

• Add excess Benedict’s reagent to the sample
• Heat the test tube in a water bath above 80C (boiling)

Question 8

What is the colour change observed if reducing sugars are present? (1)

Answer 8

• Blue to yellow-green-orange to brick red

Blue = no reducing sugars
Brick red = high reducing sugars

Question 9

Give an example of a non-reducing sugar (1)

Answer 9

Some disaccharides (e.g. sucrose)

Question 10

How do you test for non-reducing sugars? ()

Answer 10

• Add dilute hydrochloric acid (HCI) to the sample
• Heat in a water bath (to break bonds and produce monosaccharides)
• Add an alkali (e.g. NAOH) to neutralise the acid
• Add excess Benedict’s reagent to the sample
• Heat in a water bath above 80C (boiling)

Question 11

What is the colour change observed for a non-reducing sugar? (1)

Answer 11

• Blue to yellow-green-orange to brick red

Blue = no reducing sugars
Brick red = high reducing sugars

Question 12

What are some possible hazards when testing for sugars? (4)

Answer 12

• Benedict’s reagent is an irritant
• HCL is a corrosive
  NAOH is a corrosive
• Boiling water can cause burns

Question 13

State how you could measure sugars qualitatively and quantitatively (3)

Answer 13

• Qualitative - Observe the colour change from blue to brick red
• Quantitative:
  a) filter the solution and weigh the precipitate
  b) remove the precipitate and use a colorimeter to measure the absorbance of the Benedict’s reagent

Question 14

What test do you do to test for lipids? (1)

Answer 14

Emulsion test

Question 15

How do you test for lipids? (3)

Answer 15

• Add ethanol to the sample
• Shake test tube to ensure any lipids dissolve in the tube
• Add water and shake

Question 16

What should be the observable colour change if lipids are present? (1)

Answer 16

Clear to milky white

Question 17

State the qualitative and quantitative measure of lipids (2)

Answer 17

• Qualitative - observable colour change from clear to milky white
• Quantitative - none

Question 18

What hazards are there when testing for lipids? (1)

Answer 18

Ethanol is flammable

Question 19

What do you test for in proteins? (1)

Answer 19

For the presence of amino acids

Question 20

How do you test for amino acids? (2)

Answer 20

• Add excess Biuret’s reagent to the sample
• Shake thoroughly at room temperature

Question 21

What observable colour change is there if amino acids are present? (1)

Answer 21

Blue to purple

Question 22

What hazards are then when testing for amino acids? (1)

Answer 22

Biuret’s reagents is an irritant

Question 23

What is the quantitative and qualitative measures of testing for amino acids? (2)

Answer 23

• Qualitative - observable colour change from blue to purple
• Quantitative - Use chromatography to identify and separate out the different amino acids by mass

Question 24

What do you need to remember when talking about how to carry out a test? (1)

Answer 24

The specific equipment used.
e.g. add 2 drops of the reagent to a test tube with the sample