Chromatography

Question 1

Paper chromatography is used for what 2 purposes:
1.
2.

Answer 1

To separate mixtures of soluble substances

To identify substances present in the mixture.

Question 2

The more soluble a solvent is, the _______________________________.

Answer 2

further it travels up the paper

Question 3

What is the mobile phase?

Answer 3

When the solvent moves, carrying different substances with it.

Question 4

What is the stationary phase?

Answer 4

When nothing moves.

Question 5

Why do different substances (the solutes) move at different rates during the mobile phase?

Answer 5

The different dissolved substances in a mixture are attracted to the two phases in different proportions.

Question 6

Explain how paper chromatography separates substances: (3 marks).

______________ moves the ___________ through the paper.

And carries substances at _____________________.

Depending on their _________________________________.

Answer 6

Mobile phase
solvent

different distances

attraction to the solvent and paper

Question 7

A pure substance produces __________ on the chromatogram.

An impure substance produces ______________.

Answer 7

one spot

multiple spots

Question 8

What are 3 things that may go wrong in a chromatography practical?

Answer 8

The solvent line being above the start line.

The start line being drawn with ink.

No lid on the tank.

Question 9

What happens if there is no lid on the tank?

Answer 9

The water inside the tank will escape to surroundings as water vapor.

Question 10

What happens if the solvent line is above the start line?

Answer 10

The colours will dissolve.

Question 11

What happens if the start line is drawn with ink?

Answer 11

The start line will contaminate with other ink spots and make it harder to see results.

Question 12

What is the formula for rF value?

Answer 12

distance travelled by substance/ distance travelled by solvent

Question 13

How can one colour be concluded as a mixture of other colours using chromatography?

Answer 13

If their rF values are the same.

Question 14

Describe how to use paper chromatography to identify how many pigments are in an ink: (6 marks).

1. Draw a ___________________________ near the ________ of the piece of chromatography paper.
2. Place a ________________ on the ______________.
3. _________ the piece of paper into a beaker so that it doesn’t touch the sides.
4. Add a small amount of a suitable ___________ so that the level of the solvent is __________________.
5. Allow the solvent to ___________ on the paper
6. Count the _________________________ on the chromatogram.

Answer 14

horizontal line in pencil
bottom

spot of ink
pencil line

Hang

solvent
below the pencil line

rise up

number of coloured spots