Chromatography and Spectroscopy (Carbon-13 and hydrogen)

Question 1

Process of Gas Chromatography:

Answer 1

A small sample of a gaseous mixture is injected into a coiled glass elastic tube - The mixture is carried by the flow of a (noble gas) mobile phase. The mixture passes through a stationary phase (A high boiling point liquid adsorbed onto an inert solid) repeatedly. The mixture is separated due to the differing solubilities. More soluble substances diffuse more slowly across the stationary phase; This process repeats multiple coils, further seperating the substances, The gases are then detected by providing peaks at different Retention time. (Rt) Mixture them evaporate

Question 2

How are substances in a mixture seperated in Gas Chromatography:

Answer 2

The substances are seperated due to their differing solubilities causing them to travel at different speeds through the stationary phase.

Question 3

Thin Layer Chromatography: Uses

Answer 3

Used for colourless chemicals

Tests for water purity

Question 4

Thin Layer Chromatography: Mobile Phase:

Answer 4

Volatile Solvent

Question 5

Thin Layer Chromatography: Stationary Phase:

Answer 5

Silica plate with adsorbed liquid.

Question 6

Gas Chromatography: Uses

Answer 6

Testing for drugs,
Environmental analysis
Astrochemistry

Question 7

Gas Chromatography: +ves

Answer 7

Sensitive - small amounts of sample required

Good seperation of substances

Question 8

Gas Chromatography: Mobile Phase

Answer 8

Inert gases

Question 9

Gas Chromatography: Stationary Phase

Answer 9

High boiling point liquid adsorbed onto inert solid.

Question 10

Gas Chromatography: Calculating Concentration:

Answer 10

Relative abundance is used to calculate the concentration with the use of a calibration curve.

Question 11

Chemical shift range outside of 220pm on a Carbon-13 NMR represents what?:

Answer 11

Solvent, concentrations and substituents.

Question 12

What is the finger print on an IR-spectroscopy:

Answer 12

Before 1500 cm^-1 contains unique peaks used to identify particular molecule.

Question 13

C-13 NMR: Symmetrical carbons in a molecule_________

Answer 13

Symmetrical carbons in a molecule contribute to the same peak.

Question 14

Peak height is determined by what?

Answer 14

Relative abundance

Question 15

What are the labile groups? (proton NMR)

Answer 15

NH and OH, because they can dissociate in solvents. Produce a singlet on spectrum

Question 16

What is TMS?

Answer 16

(Tetramethylsilane) is chemically inert and soluble in most solvents and acts as a reference compound (0 chemical shift)

Question 17

Spin-Spin coupling:

Answer 17

the number of lines in a peak caused by the number of protons in the neighbouring environment.

Question 18

What are the +ve’s of a higher resolution NMR spectrum?

Answer 18

Different chemical shifts provide the different types of proton environments.
Number of peak areas and ‘n+1’ rule show the number of protons in environments.
D20 can be used to identify labile OH and NH groups

Question 19

True or false: Deshielding only affects proton NMR.

Answer 19

False

Question 20

How does deshielding affect NMR?

Answer 20

Deshielding affects both carbon and proton NMR, shifting their peaks to a greater chemical shift within their range.

Question 21

Why does deshielding occur?

Answer 21

An electronegative element attracts the electrons of another atom away from their nucleus. This exposes the nucleus to more of the external magnetic field

Question 22

Qualitative Analysis: Alkene

Answer 22

Add Bromine water and it will be decolourised from orange to colourless

Question 23

Qualitative Analysis: Haloalkane

Answer 23

Add silver nitrate and ethanol in a 50’C water bath

Question 24

Qualitative Analysis: Carbonyl

Answer 24

Add 2,4-dinitrophenylhydrazine ~ Orange precipitation

Question 25

Qualitative Analysis: Aldehyde

Answer 25

Add tollens’ reagent and warm ~ silver mirror

Question 26

Qualitative Analysis: Carboxylic Acid

Answer 26

Add aqueous sodium carbonate ~ effervescence

Question 27

Qualitative Analysis: Primary/Secondary alcohol and aldehyde

Answer 27

Add acidified potassium dichromate and warm in a water bath. (Colour change from orange to green)

Question 28

Use of deuterated solvents in proton NMR:

Answer 28

Prevents solvent from interfering with NMR spectrum.