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A2 Chemistry Unit 2 > Chromatography > Flashcards

Flashcards in Chromatography Deck (17)
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1

What is the definition of retention time

Time taken from injection until a component reaches the detector

2

What is the stationary phase of paper chromatography

Water absorbed

3

What is the mobile phase of paper chromatography

Liquid solvent

4

What should you do if the components of a paper chromatogram are colourless

Spray with a locating agent
Eg ninhydrin

5

What is the Rf equation

Distance moved by spot
———————————
Distance moved by solvent

6

When is two way paper chromatography used

To separate substances with similar Rf values

7

What is the stationary phase of thin layer chromatography

Layer of adsorbent particles
Eg aluminium or silica (TLC plate)

8

What does it mean when a substance is adsorbed

When it adheres to the surface

9

What is the mobile phase of thin layer chromatography

Liquid solvent

10

What is the stationary phase of gas liquid chromatography

High bp liquid or oil
Held on finely divided inert solid eg alumina/silica

11

What is the mobile phase of gas liquid chromatography

Pure inert carrier gas
Eg N2

12

How does gas liquid chromatography work

Gaseous sample mixed w inert gas
Components separate - partition themselves between mobile and stationary phase
More soluble in stationary phase - stay in coiled column longer
Components come out at different times

13

How do you work out the relative concentration of a component in gas liquid chromatography

Area under peak
————————
Total areas for all peaks

14

What is the method for running a paper/TLC chromatogram

1. Prepare concentrated solution of mixture
2. Mark origin line in pencil at bottom
X in middle of line
3. Apply conc. solution to middle of X
Using capillary tube
Allow solvent to evaporate
4. Place paper/TLC in solvent
Allow to run until solvent close to top
5. Mark solvent front
Allow to dry
6. Develop using developing agent

15

Describe the method for analysing paper/TLC chromatography

1. Mark centre of each spot
2. Distance from centre of spot to origin
3. Distance from solvent front to origin
4. Calculate Rf value

16

Describe the method for two way paper chromatography

1. Prepare a concentrated solution of mixture
2. Mark origin line in pencil near the bottom and another at 90° to this near edge of paper
3. Apply concentrated solution at intersection
Allow solvent to evaporate
4. Place in solvent
Run until solvent close to top of paper
5. Rotate through 90°
Run in different solvent
6. Develop using developing agent

17

Describe the method of analysing two way paper chromatography

1. Mark centre of each spot
2. Measure distance from centre of spot to origin
3. Measure the distance of the solvent front from the origin
4. Calculate Rf
5. Repeat for second solvent
And a second Rf value