6.3 Analysis

Question 1

Types of chromatography

Answer 1

TLC - thin layer
GC - gas

Question 2

Describe chromatography

Answer 2

A separation technique to identify chemicals in a mixture with a mobile phase (liquid/gas to carry mixture through system) and stationary phase (solid/solid-supported liquid)

Question 3

How does the mobile phase move components at varying speeds?

Answer 3

Solubility

Question 4

How does the stationary phase absorb components differently?

Answer 4

Affinity

Question 5

What is the stationary phase in TLC?

Answer 5

Typically, silica gel or aluminium oxide

Question 6

How does the solvent move up the plate in TLC?

Answer 6

By capillary action

Question 7

Name the labels on a TLC diagram

Answer 7

Solvent front
Baseline
Distance travelled by component
Distance travelled by solvent

Question 8

What is Rf?

Answer 8

Retardation factor - ranges from 0 to 1 and can be used to identify substances when compared to database values

Question 9

How do you calculate Rf?

Answer 9

Component distance travelled ÷ Solvent distance travelled

Question 10

What is the stationary phase in GC?

Answer 10

A liquid hydrocarbon with a high boiling point coating in a coiled tube kept at constant temperature

Question 11

What is the mobile phase in GC?

Answer 11

An inert carrier gas, such as Helium or Nitrogen

Question 12

What is GC used for?

Answer 12

To separate volatile components in a mixture

Question 13

How are GC results presented?

Answer 13

Forms a graph (absorption y/time x) with peaks

Question 14

How is a GC graph analysed?

Answer 14

The number of peaks is the number of components
The area under a peak is proportional to its concentration
To find the % composition of a component, find the area under its peak as a % of the total area under all peaks

Question 15

What is the equivalent of Rf for GC?

Answer 15

Retention time

Question 16

How does GC differ from TLC?

Answer 16

More sensitive - shows what chemicals are in a mixture and their concentrations
Often connected to a mass spectrometer so components can under further analysis

Question 17

Test for haloalkanes

Answer 17

Aqueous silver nitrate and ethanol
Forms different colour precipitates (Cl, Br, I)

Question 18

Test for alcohols

Answer 18

Acidified potassium dichromate turns from orange to green
Varying results based on 1°, 2°, 3° and distillation or reflux

Question 19

What isotopes are NMR active?

Answer 19

¹H and ¹³C (due to spin)

Question 21

Describe NMR

Answer 21

A non-destructive analytical technique based on ¹H and ¹³C spin alignments

Question 22

What is the reference chemical for NMR and why?

Answer 22

TMS - tetramethylsilane Si(CH3)4
Contains both C and H so can be used for both NMRs
Produces 1 sharp signal as all H’s are in same environment, and only has 1 C
Non-toxic, inert, and volatile (low b.p) so can be easily distilled off

Question 23

Importance of Deuterium in NMR

Answer 23

²H isotope is not NMR active
Solid molecules undergoing NMR need to be dissolved in a deuterated solvent to prevent swamping of graph

Question 24

What solvents are used in NMR?

Answer 24

Deuterated solvents
CDCl3 - heavy trichloromethane
CCl4 is an option but poses environmental risks

Question 25

How do you answer a ¹³C NMR question?

Answer 25

A) n of environments and ratio B) describe functional groups indicated by chemical shift ranges --> downfield means further left, carbons in same env are 'equivalents', describe height of peaks

Question 26

How do you answer a ¹H NMR question?

Answer 26

Make table of: A) functional group B) chemical shift C) H number in environment D) splitting pattern E) H number adjacent

Question 28

D2O shake

Answer 28

Due to broad and wide-ranging -OH and -NH peaks D does not produce peak D2O vigorous shake removes -OH or -NH peak to identify them

Question 29

Why are -OH and -NH peaks broad and wide ranging?

Answer 29

Due to small traces of water forming H bonds with them