Higher Chemistry- unit 3- chemical analysis

Question 1

what is chromatography

Answer 1

the term used to separate and identify components within a mixture

Question 2

how does chromatography work

Answer 2

it uses the differences in size and polarity of the molecules to separate them.

Question 3

how do you figure out the RF value

Answer 3

how far the spot has travelled/how far the water travelled

Question 4

what is the stationary phase in chromatography

Answer 4

the medium (an adsorbent material). the different components can be held to the stationary phase by Van der Waals attractions. the stronger the attractions formed between the component and the medium, the more the component is held up and therefore it travels more slowly through the medium. As different components move at different speeds through the medium, they are separated from each other

Question 5

what is the mobile phase in chromatography

Answer 5

usually a liquid or gas is used to carry the mixture through the adsorbent stationary phase. because this moves through the medium it is therefore known as the mobile phase

Question 6

why does chromatography work

Answer 6

• different molecules experience different types and strengths of intermolecular forces as the mobile phase carries them through the stationary phase. the strengths and types of force depend on the differences in polarity and size of the molecule being separated
• molecules that form stronger intermolecular forces with mobile phase than the stationary phase will move quicker than other molecules that form stronger intermolecular bonds with the stationary phase
• like dissolves like e.g. if the mobile phase is polar and the stationary phase is non polar expect any polar molecules to move further and faster than any non-polar molecules.

Question 7

what is the mobile phase in paper chromatography

Answer 7

liquid solvent

Question 8

what is the mobile phase in thin-layer chromatography

Answer 8

liquid solvent

Question 9

what is the mobile phase in gas-liquid chromatography

Answer 9

unreactive gas

Question 10

what is the stationary phase in paper chromatography

Answer 10

paper

Question 11

what is the stationary phase in thin-layer chromatography

Answer 11

silica coating on a plastic film

Question 12

what is the stationary phase in gas-liquid chromatography

Answer 12

non volatile liquid sticking to an unreactive solid

Question 13

what are the 3 types of chromatography

Answer 13

• paper chromatography
• thin layer chromatography
• gas liquid chromatography

Question 14

what is the retention time in chromatography

Answer 14

the time taken for a particular component to travel through the apparatus.

Question 15

what is a standard solution

Answer 15

a solution of accurately known concentration

Question 16

how do you prepare a standard solution

Answer 16

1. calculate mass of the solute you require to make your solution mass=n x GFM
2. accurately weigh solute into a small clean beaker
3. dissolve solute using a minimum volume of distilled water (no more than a 1/4 of the total volume of solution
4. use a funnel to pour the solution into your standard flask
5. using distilled water (no more than 1/4 of the total volume of solution) rinse your beaker and pour these washings into the standard flask. repeat once more
6. using distilled water make up to the mark on your standard flask
7. stopper and invert to mix thoroughly

Question 17

how do you figure out a colour change

Answer 17

it goes from the colour of the thing in the flask–> colour of thing in burette

Question 18

what are mistakes during a titration

Answer 18

• misjudging end point

- human errors

Question 19

what is volumetric analysis

Answer 19

involves using a solution of accurately known concentration in a quantitative reaction to determine the concentration of another substance.

Question 20

how is the volume of reactant solution required to complete the reaction determined

Answer 20

by titration

Question 21

what is the end point

Answer 21

the point at which the reaction is just complete

Question 22

what is an indicator

Answer 22

a substance which changes colour at the end-point