Analysis 2

Question 1

Explain the relationship between temperature and retention time

Answer 1

Inverse proportionality
The greater the temperature, the greater the energy of the particles and so more likely the gas state so the faster it travels causing a lower retention time

Question 2

Give 2 main uses for GC

Answer 2

1) Separating our mixtures
2) Calculating the amount of proportions of the components in a mixture

The concentrations are proportional to the area under peaks on an adsorption time graph

Question 3

Explain the reaction of OH/NH protons with and without D2O

Answer 3

Peaks are normally broad and so have no splitting and are difficult to identify. When mixed with D2O peaks disappear

Question 4

Explain what retention time tells us about a compound’s solubility

Answer 4

The greater the solubility, the lowers the retention time as it isn’t carried by the gas mobile phase

Question 5

Explain how NMR is used

Answer 5

NMR is a non destructive technique used the analyse radio wave energy requires to flips the signs of certain isotopes in a magnetic field. The energy required dependant on chemical environments can be used to work out the different kinds of isotope atoms

Question 6

Define retention time

Answer 6

The time between injection and detection

It is the equivalent for Rf value for TLC

Question 7

Explain what the splitting tells you in NMR

Answer 7

Remember the n - 1 rule where n represents the splitting shown. This indicates the number of hydrogens or carbons in neighbouring environments.

Question 8

Give 2 main uses for TLC

Answer 8

1) Assess purity of a compound
—> analytical technique
2) Monitor progress of reaction

Question 9

Define the Rf value

Answer 9

Distance travelled by component / distance travellers by solvent front

Question 10

Explain the stationary phase in TLC

Answer 10

Thin piece of inert material on glass

Question 10

Explain what the Rf value shows about the relative adsorption strength of the compound

Answer 10

The higher the spot, the lower the polarity
- Similar polarity = low Rf value
Due to stronger adsorption
- Difference in polarity = High Rf value
Due to lower adsorption

Question 10

Explain how you could predict the number of peaks in a compound

Answer 10

Number of UNIQUE carbon environments.

Look for symmetry to cancel out of these will have repetitive carbon environments

Question 12

Explain what the area under H NMR peaks mean

Answer 12

The integral represents the ratio of protons in each environment

Question 13

Explain the mobile phase in TLC

Answer 13

Organic solvent which moves vertically up the TLC plate

Question 14

Explain the stationary phase in GC

Answer 14

Liquid / solid coating on inside of tube

Question 17

Explain why compounds with similar Rf values can cause issues in analysis

Answer 17

Causes the overlap of component of compound and so unable to distinguish the between compounds and their Rf Values

Question 18

Explain the mobile phase in GC

Answer 18

Inert carrier gas

e.g helium / nitrogen

Question 21

Explain why we use deuteriated solvents in NMR

Answer 21

Deuterium doesn’t have spin and so can be substituted for hydrogens in common solvents.
e.g CDCl3 commonly used

Question 22

Explain why we use TMS in NMR

Answer 22

Tetramethylsyline is used as an internal standard. This is because it’s carbons have a low chemical shift and so most carbon environments appear above it. In addition it produces a strong and distinct singlet