Topic 19

Question 1

What is a high resolution mass spectrometer and why is it used instead of a low level one

Answer 1

Measures the Ar to several decimal places so makes it better to use to distinguish between compounds of a similiar Mr

Question 2

Why is NMR used
Define the 2 types

Answer 2

NMR(Nucleur magnetic resonance) spectroscopy is used to help determine the structure of a molecule

C13 NMR- tells us information on how carbon atoms are rearranged
1H NMR- tells us information on how hydrogen is rearranged

Question 3

Explain the movement of nuclei spin before and after an external magnetic field is applied

Does NMR emit radio waves

Answer 3

Nuclei spins in random directions before an external magnetic field is applied

However, when it is applied, they either spin in the same direction or against it

Yes NMR does emit radio waves

Question 4

What does NMR actually measure

Answer 4

Measures the amount of energy absorbed this is because initially

There is more nuclei aligned with the magnetic field so more energy is absorbed

Question 5

Characteristics of TMS and what is it and why is it used as the reference point

Answer 5

TMS has one carbon and 1 hydrogen environment
Produces a large single peak upfield from all other peaks
It is inert, non toxic and volatile

Question 6

What is TLC

Answer 6

Thin layer chromatography allows us to separate and identify compounds

Question 7

What are the stationary and mobile phases of TLC and explain how does it work

Answer 7

1) draw a pencil line 1cm away from bottom of paper and add a drop of mixture on the line
2) Use a stationary phase of Silica/aluminium gel on the glass plate
3. Place in solvent(mobile phase)
4. Allow solvent to move up to near the top of the table. Remove and allow to dry
5. Calculate Rf

Question 8

Calculate Rf value formula

Answer 8

Distance moved by spot/ distance moved by solvent

Question 9

Purpose of Gas Chromatography

Answer 9

Is useful to separate a mixture of liquids that are volatile

Question 10

What is the Gas chromatography mobile and stationary phases

Answer 10

GC is you have a thin column wound up inside in the oven

Column is a solid or viscous liquid(stationary phase)

Sample is injected and carried by an inert gas( mobile phase)

Question 11

What is retention time

Answer 11

Length of time is takes for substance to go from stationary phase to detector

Question 12

Purpose of HPLC(high performance liquid chromatography)

Answer 12

Used instead of Gas Chromatography when a sample has a high boiling point or decomposes in heat

Question 13

What is the mobile and stationary phase of HPLC

Answer 13

Stationary phase- small solid particles( Silica) in a column

Mobile phase - A polar liquid( methanol and water mix)

Question 14

How HPLC works

Answer 14

HPLC solvent is pressurised using a pump to which the sample under test is added and pushed through the column

Question 15

Explain the attraction between component spot with stationary and mobile phase if the RF value is very high in TLC

Answer 15

The attraction between component spot and stationary phase(silica gel plate) is weak

Attractions between component and solvent(mobile phase) is strong

Question 16

Explain what will happen to the RF value if a polar substance is used in TLC which has a non polar solvent

Answer 16

The mobile phase will be weak as polar is not soluble in non polar so RF value is low

Question 17

What are the factors affecting retention time in Gas Chromatography and explain them

Answer 17

Polarity/solubility of the component on the stationary phase- greater attraction means greater retention time

Boiling temperature of the compound- higher boiling temperature compounds spend less time in the gas phase(mobile phase) so have higher retention time