Chapter 29 - Chromatography and spectroscopy

Question 1

what information does thin layer chromatography give?

Answer 1

The number of components in a mixture

Question 2

what is adsorption?

Answer 2

The process by which the solid holds the different substances in the mixture to its surface

Question 3

How is separation achieved in TLC?

Answer 3

The relative adsorption of substances within the stationary phase

Question 4

What needs to be calculated from a TLC plate?

Answer 4

The retention factor

Question 5

what is the equation for retention factor?

Answer 5

Distance moved by the component divided by distance moved by the solvent front

Question 6

What is gas chromatography useful for?

Answer 6

Separating and identifying volatile organic compounds

Question 7

in gas chromatography, what is the stationary phase?

Answer 7

A high boiling liquid absorbed onto an inert solid support

Question 8

In gas chromatography, what is the mobile phase?

Answer 8

an inert carrier gas

Question 9

what two pieces of information can be obtained from a gas chromatogram?

Answer 9

The retention times and the peak integrations

Question 10

what is the chemical test and positive observation for alkenes?

Answer 10

add bromine water drop wise, it will be decolourised from orange to colourless

Question 11

what is the chemical test and positive observation for Halo alkanes?

Answer 11

Add silver nitrate and ethanol and warm to 50°,
chloro - white precipitate
bromo - cream precipitate
iodo - yellow precipitate

Question 12

what is the chemical test and positive observation for a carbonyl?

Answer 12

add 2,4-DNP, orange precipitate

Question 13

what is the chemical test and positive observation for a primary and secondary alcohol and aldehyde?

Answer 13

Add a acidified potassium dichromate and warm, colour change from orange to green

Question 14

what is the chemical test and positive observation for aldehydes?

Answer 14

Add Tollen’s reagent and warm
, silver mirror

Question 15

what is the chemical test and positive observation for a carboxylic acid?

Answer 15

Add aqueous sodium carbonate, effervescence

Question 16

what is resonance?

Answer 16

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

Question 17

what is measured on an NMR spectroscopy?

Answer 17

The chemical shift

Question 18

what is used as a standard reference for chemical shift?

Answer 18

TMS

Question 19

why is a deuterated solvent used?

Answer 19

so the H1 peaks don’t appear

Question 20

what two pieces of information does C - 13 NMR show?

Answer 20

the number of different carbon environments and the types of carbon environments

Question 21

what four pieces of information does proton NMR give?

Answer 21

• the number of different proton environments
• the types of proton environments
• the relative numbers of each type of proton
• the number of non-equivalent protons adjacent to a given proton

Question 22

On an NMR spectra, how do we see the number of different proton environments?

Answer 22

the number of peaks

Question 23

On an NMR spectra, how do we see the types of proton environment?

Answer 23

chemical shift

Question 24

On an NMR spectra, how do we see the relative numbers of each type of proton?

Answer 24

integration traces/ ratio numbers of the relative peak areas

Question 25

On an NMR spectra, how do we see the number of non-equivalent protons adjacent to a given proton?

Answer 25

spin-spin splitting pattern

Question 26

what rule is needed when analysing the splitting pattern?

Answer 26

n+1

Question 27

what is different about OH and NH in proton NMR

Answer 27

they can appear at a range of chemical shift values and as broad peaks

Question 28

how is the problem with OH and NH in NMR spectroscopy overcome?

Answer 28

D2O is added which replaces them and removes the peak

Question 29

what order should all analytical techniques be done in?

Answer 29

1) Elemental analysis 2) Mass spectra 3) Infrared spectra 4) NMR spectra