Topic 19
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What is a high resolution mass spectrometer and why is it used instead of a low level one
Measures the Ar to several decimal places so makes it better to use to distinguish between compounds of a similiar Mr
Why is NMR used Define the 2 types
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
Explain the movement of nuclei spin before and after an external magnetic field is applied Does NMR emit radio waves
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
What does NMR actually measure
Measures the amount of energy absorbed this is because initially There is more nuclei aligned with the magnetic field so more energy is absorbed
Characteristics of TMS and what is it and why is it used as the reference point
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
What is TLC
Thin layer chromatography allows us to separate and identify compounds
What are the stationary and mobile phases of TLC and explain how does it work
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
Calculate Rf value formula
Distance moved by spot/ distance moved by solvent
Purpose of Gas Chromatography
Is useful to separate a mixture of liquids that are volatile
What is the Gas chromatography mobile and stationary phases
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)
What is retention time
Length of time is takes for substance to go from stationary phase to detector
Purpose of HPLC(high performance liquid chromatography)
Used instead of Gas Chromatography when a sample has a high boiling point or decomposes in heat
What is the mobile and stationary phase of HPLC
Stationary phase- small solid particles( Silica) in a column Mobile phase - A polar liquid( methanol and water mix)
How HPLC works
HPLC solvent is pressurised using a pump to which the sample under test is added and pushed through the column
Explain the attraction between component spot with stationary and mobile phase if the RF value is very high in TLC
The attraction between component spot and stationary phase(silica gel plate) is weak Attractions between component and solvent(mobile phase) is strong
Explain what will happen to the RF value if a polar substance is used in TLC which has a non polar solvent
The mobile phase will be weak as polar is not soluble in non polar so RF value is low
What are the factors affecting retention time in Gas Chromatography and explain them
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