F324 - Analysis

Question 0

How does a liquid stationary phase seperate?

Answer 0

By relative solubility.

Question 1

How does a solid stationary phase seperate?

Answer 1

By adsorption

Question 2

What can be a mobile phase?

Answer 2

Liquid or gas.

Question 3

What can a stationary phase be?

Answer 3

A solid, liquid, or solid on a solid support.

Question 4

Describe how chromatography works.

Answer 4

Different components have different affinities for a stationary phase and for a mobile phase.

The stationary phase interacts with the components in the mixture, slowing them down.
The greater the interaction the more the components are slowed down.

This allows different components to flow over the stationary phase at different speeds, separating the components.

Question 5

What are the two types of chromatography?

Answer 5

Thin layer - the stationary phase is a solid, and the mobile phase is liquid.

Gas - the stationary phase is liquid or solid on a solid support, and the mobile phase is gas.

Question 6

What is adsorption?

Answer 6

The process by which a solid holds molecules of a gas or liquid or solute as a thing film on the surface of a solid or more rarely a liquid.

Question 7

What is a chromatogram?

Answer 7

A visible record showing the result of separation o the components of a mixture by chromatography.

Question 8

What is Rt?

Answer 8

Distance moved by component/

Distance moved by solvent front

Question 9

Describe thin layer chromatography.

Answer 9

Stationary phase is a thin later of an adsorbent such as silica gel coated on a sheet of glass or plastic. This is the TLC plate.

The mobile phase is a liquid solvent which moves vertically up the TLC plate.

Question 10

How do you produce a chromatogram?

Answer 10

A small sample of the mixture is dissolved.

A small spot of the sample is placed on the TLC plate a short distance from one end.

The sample spot is left to dry and the TLC plate is place in a jar containing a shallow layer of solvent below the sample spot.
The jar is sealed to slow down the evaporation of solvent from the TLC plate.

As the solvent rises it meets the sample and the mixture is swept upwards with the solvent.
Separation is achieved by adsorption, as some bind to to adsorbent strongly and some weakly, they travel different distances up the TLC plate as a result.

Question 11

Describe adsorption and relative solubility.

Answer 11

Huh

Question 12

Describe limitations of thin layer chromatography.

Answer 12

Similar compounds have very similar Rf values.

Only works for known compounds, unknown compounds have no Rf for comparison.

A suitable solvent can be hard to find, if the components are very soluble they will be washed up with the solvent front.
If they are insoluble they will hardly move.

Question 13

What is retention time?

Answer 13

In gas chromatography, the time for a component to pass from the column inlet to the detector.
Compared to known times of other compounds.

Question 14

When Is gas chromatography used?

Answer 14

To separate volatile components in a mixture.

Useful for compounds with a low boiling point and evaporate easily.

Question 15

Describe where gas chromatography takes place and it’s phases.

Answer 15

In a gas chromatograph.

The stationary phase is a thin layer of a liquid or solid, coated on by inside of some capillary tubing, which is inert solid support. Wound into a coil.
The tubing is the chromatography column.
The liquid for the stationary phase is often a long alkane with a high boiling point.

The mobile phase is a carrier inert gas which moves through the column, such as helium or nitrogen.

Question 16

Describe how a gas chromatogram is produced.

Answer 16

The mixture is injected into the gas chromatograph, where it is vaporised.

The mobile carrier carries it through the tube and over the stationary phase.

The components constantly dissolve in the stationary phase, evaporate into the mobile phase and then re dissolve as they travel through the tube.

Each component leaves the column at a different time and is detected as it leaves the column, a computer processes the results to display a gas chromatogram.

Question 17

What are limitations of gas chromatography?

Answer 17

Thousands of chemicals could have the same retention time, so does not identify all components.

Unknown compounds have no reference retention times for comparison.

Question 18

Dat combining thing yeah?

Answer 18

Gas chromatography is often combined with mass spectrometry.

GC can separate components without identifying them.
MS can provide structural information without separating them.

Question 19

State uses of GC-MS.

Answer 19

Forensics - drug identification.

Environmental analysis - monitoring pollutants and pesticides.

Airport security - explosives

Space probes - detect elements on other planets.

Question 20

What is chemical shift?

Answer 20

A scale that compares the frequency of an NMR adsorption with the frequency of the reference peak of TMS at 0ppm.

Question 21

Why do different parts of the mixture travel different distances in TLC?

Answer 21

Depends on attraction to the stationary phase - adsorption.

A strongly attracted substance will move slowly.

Question 22

Why are different retention times recorded for Gas chromatography?

Answer 22

The solubility determines how long the component spends dissolved in the stationary phase and how long it spends moving along the tube in he mobile phase.
A high solubility will take more time dissolved and longer to travel through to the detector.

Question 23

On a gas chromatogram what shows the amount of each substance?

Answer 23

The area under the curve.

Question 24

How do you find the retention time on a gas chromotogram?

Answer 24

Measure from zero to the centre of the peak.

Question 25

Stuff on page 85

TMS and CDCL3 for NMR

Answer 25

Nop