29 Chromatography and spectroscopy

Question 1

What is gas chromatography (GC) used for?

Answer 1

To separate volatile liquids.

Question 2

What happens in gas chromatography (GC)?

Answer 2

• A small amount of the volatile mixture is injected into the apparatus
• The mobile carrier gas carries the components through the column (inside a thermostatically controlled oven) where it separates into different liquids
• Slower it moves–> greater affinity with stationary phase
• Produces a chromatagram

Question 3

What is the mobile phase of GC?

Answer 3

An inert gas (e.g. nitrogen)

Question 4

Wat is the stationary phase of GC?

Answer 4

Solid/ high boiling point liquid coated on a solid support

Question 5

What do the number of peaks on a GC chromatogram represent?

Answer 5

The number of substances in the mixture.

Question 6

What does the area under each peak represent on a GC chromatogram?

Answer 6

The relative amount of the substance in the mixture

Question 7

What is the test for an alkene?

Answer 7

Add bromine water
Orange –> colourless

Question 8

What is the test for the halogens?

Answer 8

Add silver nitrate and ethanol at 50 degrees
Chloro- white
Bromo- Cream
Iodo- Yellow

Question 9

What is the test for a carbonyl group?

Answer 9

Add 2,4-DNP
Orange precipitate

Question 10

What is the test for an aldehyde group?

Answer 10

Add Tollens reagent + warm
Silver mirror

Question 11

What is the test for a primary/secondary alcohol?

Answer 11

Add K2Cr2O7 + warm
Orange –> Green

Question 12

What is the test for a carboxylic acid?

Answer 12

Add NaCO3 (aq)
Fizzing

Question 13

What is the test for a phenol?

Answer 13

Bromine water
White precipitate

Question 14

What is resonance?

Answer 14

When the nucleus can absorb energy and rapidly flip between the two spin states.

Question 15

What is used in a NMR spectrometer?

Answer 15

A super-conducting electromagnet, cooled by liquid helium.

Question 16

What is chemical shift in NMR?

Answer 16

When the electrons in atoms shift the energy and radio frequency needed for NMR.

Question 17

What is the unit for chemical shift?

Answer 17

ppm

Question 18

What substance is used as a standard reference in NMR?

Answer 18

TMS- has a chemical shift of 0ppm

Question 19

What happens when deuterium oxide is added to a H NMR spectrum reading, and why?

Answer 19

Any O-H or N-H peaks disappear, because the hydrogen gets replaced by a D, meaning it isn’t detected.

Question 20

What do the areas under a proton NMR spectra tell us?

Answer 20

The relative number of each type of proton.

Question 21

What is the splitting rule in proton NMR?

Answer 21

For a proton with n protons attached to an adjacent carbon atom, the number of sub-peaks in a splitting pattern is n+1.

Question 22

What is the chemical environment of a carbon determined by?

Answer 22

The position of the atom within the molecule and symmetry.