Chapter 29 - Chromatography and Spectroscopy

Question 1

Define polar substances

Answer 1

There is a net dipole on the molecule.

Question 2

Define a stationary phase

Answer 2

A solid or liquid that doesn’t move at all.

Question 3

Define the mobile phase

Answer 3

The phase that moves through the chromatography.

Question 4

Define the retardation factor

Answer 4

The distance travelled by a solute compared to the solvent.

Question 5

Define the retention factor

Answer 5

In gas chromatography, it is the time taken to travel through the column.

Question 6

Define adsorption

Answer 6

How well something can hold onto the surface of another substance.

Question 7

Define absorption

Answer 7

The process by which atoms enter another phase.

Question 8

TLC Polarity

Answer 8

Generally, the stationary phase (silica gel) is polar, and the mobile phase is non polar.
This way, depending on the polarity of the components in the mixture, different compounds will travel different distances up the plate.
The more polar the compound in the mixture, the less it will travel up the plate, because it will be attached to the stationary phase more.

Question 9

Methods of identification for TLC

Answer 9

1. UV light
2. Ninhydrin for Amino acids (because they are colourless)
3. Iodine crystals

Question 10

GC - How are the solutes separated?

Answer 10

1. Based on solubility in the stationary phase and boiling points.
2. The compounds of high solubility and higher b.p, is more likely to travel slower.

Question 11

What are the factors that affect the retention time?

Answer 11

Individual compounds: 
- Solubility in the stationary phase 
- Boiling point of the component. 
All compounds:
- Length of the column 
- Packing material 
- Type of carrier gas
- Flow rate of carrier gas 
- Temperature of column

Question 12

Examples of carrier gas

Answer 12

Helium or neon

Question 13

GC - What are the axes of a chromatogram

Answer 13

X- Axis: Retention time

Y-axis: idk

Question 14

How to read a GC Chromatogram

Answer 14

Each peak is a different component itself.

The area under each peak is the amount of the compound.

Question 15

6 marker:

How to carry out a TLC

Answer 15

1. Take a TLC plate and using a pencil, draw a line 1cm from 1 end of the plate (baseline)
2. Using a capillary tube, add the solution onto the baseline (just a spot)
3. Prepare the chromatography tank, by pouring in some solvent in a depth of 0.5cm.
4. Place the TLC plate into a beaker, make sure that the solvent can’t reach the spot. Cover with the watch glass and wait.
5. Allow to rise till it gets to 1cm of the other end.
6. Remove and mark the solvent front. Allow to dry.
7. Circle any visible spots

Question 16

How to calculate Rf value

Answer 16

Rf = (component)/ solvent.

Question 17

GC- Concentrations of components

Answer 17

1. Prepare standard solutions of known concentrations. 2. Obtain gas chromatogram for each.
2. Plot a calibration curve of peak area against concentration, this is called external calibration.
3. Obtain the gas chromatogram of unknown compounds and use the curve to measure the concentration of those compounds.