Required practicals 🥼🧪

Question 1

What does paper chromatography allow us to do?

Answer 1

• paper chromatography, allows us to separate different substances based on their different solubilities.

Question 2

Describe a method you would do to carry out paper chromatography [5]

Hint: draw, pipette, place, solvent, dry

Answer 2

• draw a pencil line across chromatography paper (about 1 cm above the bottom)
• use a pipette, or capillary tube, to add small spots of each ink (A,B, C and D) to the line on the paper, as well as unknown ink (U) (equally spread across the paper)
• place the paper into a container with a suitable solvent (e.g. water) in the bottom - making sure the pencil line is above the water line
• and allow the solvent to move through the paper, but remove the chromatogram before it reaches the top
• then allow the chromatogram to dry, and measure the distance travelled by each spot and by the solvent

Question 3

With chromatography, is there a limit to how many substances we can test?

Answer 3

• no, with chromatography this can be done with several colours; there has to be enough space on the paper.

Question 4

What is the stationary phase in paper chromotography ?

Answer 4

• In paper chromatography, the stationary stage is called the paper- because it doesn’t move.

Question 5

What is the mobile phase in paper chromatography?

Answer 5

• In paper chromatography, the mobile phase is the solvent- since it does move.

Question 6

In chromatography, what’s the difference between the stationary 🆚️ mobile phase?

Answer 6

• the stationary stage is called the paper- because it doesn’t move
• ; the mobile phase is the solvent- since it does move.

Question 7

In paper chromatography, how do we know if a colour is a single substance?

Answer 7

• there will be only one spot

Question 8

How do we know in paper chromatography, that a colour is a mixture of two different substances?

Answer 8

• the colour will separate into two different spots.

Question 9

Why does paper chromatography work? [3]

Answer 9

• paper chromatography works, because each chemical in the mixture will be attracted to the stationary phase (the paper), to a different extent.
• and chemicals that are strongly attracted to the stationary phase (the paper) will not move very far.
• chemicals that are weakly attracted, will move further up the paper.

Question 10

What will a pure chemcial produce, 🆚 chemicals in a mixture?

Answer 10

• a pure chemical produces singles spot in all solvents
• ; a chemical in a mixture may separate into different spots, based on the solvent.

Question 11

In paper chromatography, why do we draw our starting line in pencil instead of pen ?

Hint: ⬆️

Answer 11

• We draw our starting line in pencil, since if it was in pen: the pen ink would move up the paper with the solvent.

Question 12

What is the calculation for Rf value ?

Answer 12

Rf value= distance moved by substance ➗ distance moved by solvent