Separation techniques

Question 1

define:

solution

Answer 1

a solute in a solvent
e.g. salt water

Question 2

What is meant by ‘soluble’

Answer 2

a substance that can dissolve in a solvent

Question 3

define :

solute

Answer 3

a substance that is dissolved in a solvent

e.g salt

Question 4

define:

solvent

Answer 4

a liquid in which chemicals dissolve to make a solution

e.g. water or ethanol

Question 5

define:

non-aqueous solution

Answer 5

solution where the solute is dissolved in a solvent that isn’t water

e.g. ethanol

Question 6

define:

aqueous solution

Answer 6

solution where the solute is dissolved in water

Question 7

chromotography:

what is refererred to as the:

• STATIONARY phase

-MOBILE phase

Answer 7

• STATIONARY phase (stays still) = the paper

-MOBILE phase (moves) = the solvent

NOTE:
So why not just say paper and solvent?

-Because not all chromatography uses paper.

-Not all mobile phases are the same solvent.

-Exams want you to show you understand the function, not just the material.

Question 8

What is the pencil line?

Answer 8

The line drawn in pencil near the bottom of the chromatography paper where the sample is placed. (Pencil is used because it does not dissolve (not soluble) in the solvent.)

Question 9

Why is pencil used instead of pen?

Answer 9

Pen ink would dissolve as it is soluble in water and move with the solvent, ruining the results.

Question 10

What is the solvent front?

Answer 10

The furthest point the solvent reaches on the (chromatography) paper

Question 11

MEMORISE (GAP FILL)

Chromatography :

separates coloured …… which are …… in a solvent

-the solvent carries different ……. compounds different …….

-distance carried depends on the ….. of the colour particles

-the more/less soluble a compound , the further it travels with the …..

Answer 11

separates coloured COMPOUNDS which are SOLUBLE in a solvent

-the solvent carries different COLOURED compounds different DISTANCES

-distance carried depends on the SOLUBILITY of the colour particles

-the MORE soluble a compound , the further it travels with the SOLVENT

NOTE:
It depends on solubility:
-If a colour is very soluble, it likes the solvent.
-If it’s less soluble, it sticks more to the paper.

More soluble → goes further

Less soluble → stays nearer the start

Question 12

What does Rf stand for ?

Answer 12

Retention factor

Question 13

True or False:

The Rf value is never greater than 10

Answer 13

FALSE: (true but number should be 1 as the dye can’t travel further than the solvent)

the Rf value is never greater than 1

Question 14

What is the formula used to calculate Rf value?

Answer 14

Rf =
distance moved by sample
——————————-distance moved by solvent

Question 15

What is the unit for Rf value?

Answer 15

Rf values don’t have units as they cancel

• ensure that they are the SAME units

Question 16

What does it mean if 2 compounds have the same Rf value ( using same solvent) ?

what would happen if the solvent changed?

Answer 16

the compounds are the same

• ! Rf values are the same for a specific compound in a particular substance / solvent

-If the solvent changed, the Rf value will be DIFFERENT

NOTE: A specific compound gives the same Rf value as long as the same solvent is used, so Rf values can be used to identify substances.

Question 17

Suggest a reason why a lid would be needed if the solvent used was ETHANOL

Answer 17

If ethanol is used as a solvent, a lid would be needed as it EVAPOURATES EASILY

• (at a lower temperature than water)

Question 18

Why do you need a pencil line?

Answer 18

This marks where inks were placed at the start

• pencil is insoluble in most solvents and won’t dissolve or move with the solvent (doesn’t affect results)

Question 19

What does it mean if there are multiple dots?

Answer 19

Th ink is a mixture of different substances (compounds)

Question 20

What does it mean if the mixture (ink) doesn’t separate ?

Answer 20

substance is insoluble in the solvent

Question 21

What does CHROMOTOGRAPHY separate?

Answer 21

dissolved substances from a mixture

Question 22

What does FILTRATION separate?

Answer 22

an insoluble solid from a liquid (mixture)

Question 23

What does DISTILLATION separate?

Answer 23

a solute from a solution

Question 24

What does EVAPOURATION separate?

Answer 24

a dissolved solute from a solution