Tests

Question 1

Biuret test for proteins

Answer 1

Biuret solution turns from blue to violet

Question 2

Benedict’s test for reducing sugars

Answer 2

Benedicts reagents turns from aqua-blue to yellow to orange when heated in the presence of reducing sugars

Question 3

Reagent test strips for reducing sugars

Answer 3

Strips change colour depending on level of glucose, can be checked using a chart

Question 4

Emulsion test for lipids

Answer 4

A layer of cloudy white suspension for,s at the top of the solution if lipids present

Question 5

Iodine test for starch

Answer 5

Solution turns from orange brown to deep blue

Question 6

Benedict’s test for non-reducing sugars

Answer 6

• stays blue (no sugar)
• yellow (low amount)
• brick-red (high amount)

Question 7

Rf =

Answer 7

Distance moved by solute / distance moved by solvent

Question 8

What can we seperate using TLC

Answer 8

Amino acids

Question 9

What happens in the mobile phase

Answer 9

The mobile phase (an organic solvent) picks up the amino acids and moves through the stationary phase where they are seperated

Question 10

Why do students wear gloves during chromatography and only handle the edge of the plate

Answer 10

To avoud contaminating the stationary phase

Question 11

Why is a mixture of solvents used in the TLC of amino acids

Answer 11

The different solvents will dissolve both polar and non polar compounds in case the compound is unknown and we don’t know its properties

Question 12

Why do we seal the jar of solvent

Answer 12

So the air inside is saturated with solvent & to prevent evaporation

Question 13

Amino acids react with ninhydrin to form what colour spot

Answer 13

Purple / brown

Question 14

The rate at which amino acids move through the silica gel depends on

Answer 14

The interactions (H bonds) they have with the silica in the stationary phase, and their solubility in the mobile phase

Question 15

How does a colorimeter work

Answer 15

• A colorimeter is a piece of equipment used to quantitively measure the absorbance, or transmission, of light by a colored solution.
• As the glucose concentration in the sample rises, the proportion of Benedict’s reagent decreases, making the glucose solution less tinted and therefore less viable to the absorption of light. This means that the transmission percentage of red light increases as less light is being absorbed.