Brainscape's Knowledge GenomeTM

Browse over 1 million classes created by top students, professors, publishers, and experts.


See full index

chemistry module 6 > chromatography + qualitative analysis + NMR > Flashcards

chromatography + qualitative analysis + NMR Flashcards

You may prefer our related Brainscape-certified flashcards:
AP® Chemistry flashcards Periodic Table flashcards Chemistry 101 flashcards Organic Chemistry 101 flashcards
1
Q

what is the purpose of chromatography

A

used to separate individual components from a mixture of substances

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
2
Q

2 components of chromatography

A

stationary phase and mobile phase

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
3
Q

what are the stationary and mobile phases in TLC

A

stationary - silica gel (SiO2) / TLC plate
mobile phase - solvent

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
4
Q

what are some uses of chromatography

A

analysis of drugs, flavourings, plastics, air samples, forensic science

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
5
Q

what does TLC stand for

A

thin layer chromatography

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
6
Q

in TLC how does separation occur

A

by relative adsorption - different components in the mixture adsorb differently to the surface of the stationary phase

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
7
Q

adsorption definition

A

how much interaction components have with the stationary phase - higher adsorption = lower Rf

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
8
Q

Rf equation

A

distance travelled by component / distance travelled by solvent -

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
9
Q

what are 4 limitations of TLC

A
  • difficult to measure the exact middle of the component spot
  • similar compounds have similar Rf values, can be difficult to tell them apart or spots may be overlapping
  • difficult to find a solvent that dissolves all components in a sample
  • there may not be a reference chromatogram that exists in the database e.g. for an unknown compound
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
10
Q

what is the purpose of gas chromatography

A

used to separate volatile compounds in a mixture - it is also useful for analysing organic compounds with low boiling points

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
11
Q

volatility definition

A

the tendency of a compound to vaporise / turn into a gas

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
12
Q

what are the stationary and mobile phases in gas chromatography

A

stationary - high boiling point liquid adsorbed onto inert solid support
mobile - inert carrier gas e.g. a noble gas

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
13
Q

how are substances separated in gas chromatography

A

by relative solubility

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
14
Q

retention time definition

A

time taken for a compound takes to travel trhough the column

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
15
Q

how are components represented on gas chromatograms

A

by peaks

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
16
Q

how are gas chromatograms interpreted

A

retention times can be used to identify compounds by comparing them to retention times for known components

peak integration can be used to determine the concentration of components - area of the peaks is proportional to the amount of the component in the sample

17
Q

formula for % of a component in the mixture

A

( area of peak / total area of all peaks ) x 100

18
Q

what are 3 limitations of gas chromatography

A
  • compounds may have the same retention times
  • small amount of one component may hide behind a component with a higher concentration
  • unknown components will not have any retention time data to compare
19
Q

outline a chemical test to identify an alkene

A

react with bromine water
POSITIVE = decolourises

20
Q

outline a chemical test to identify a haloalkane

A

react with AgNO3(aq)
POSITIVE = a coloured precipitate forms
Cl - white precipitate
Br - cream precipitate
I - yellow precipitate

then dissolve in NH3
Cl - dissolves in dilute NH3
Br - dissolves in conc NH3
I - insoluble in NH3

21
Q

outline a chemical test to identify a carbonyl group

A

react with 2,4-DNP
POSITIVE = orange-yellow solution becomes an orange precipitate

22
Q

outline a chemical test to identify an aldehyde

A

react with tollens reagent
POSITIVE = silver mirror forms

23
Q

outline 2 chemical tests to identify a phenol

A

react with bromine water
POSITIVE = decolourises + white precipitate 2,4,6-tribromophenol forms

react with Na
POSITIVE = fizzing + effervescence will occur

24
Q

outline a chemical test for a carboxylic acid

A

react with NaCO3 then bubble this gas through limewater
POSITIVE = effervescence + gas turns limewater cloudy

25
Q

outline a chemical test for an acyl chloride

A

react with water
POSITIVE = white fumes of HCl given off

26
Q

what does NMR stand for

A

nuclear magnetic resonance

27
Q

how does NMR work

A
  • it uses a combination of very strong magnetic fielf strength and radio frequency radiation
  • with the right combination of the two, the nuclei of some atoms can absorb this radiation, and the energy for absorption can be measured and recorded as an NMR spectrum
28
Q

what are the 2 types of NMR

A

carbon 13 NMR and proton NMR

29
Q

nuclear spin definition

A

the nucleus has 2 different spin states with different energies

this is significant for particles with an odd number of particles in the nucleus - this is why 13C isotope is used

30
Q

resonance definition

A

with the right combination of magnetic field and radio frequency radiation the nucleus can absorb energy and rapidly flip between the 2 states - this is resonance

31
Q

what reference chemical is used in NMR + why

A

TMS - it is given a shift value of 0ppm, so all shift values are relative to TMS
- it is chemically unreactive
- it has 12 equivalent protons and 1 carbon environment, giving a sharp easily measured peak in 13C and H NMR
- nuclei are heavily shielded so rarely peaks below it
- volatile so easily removed from the sample after

32
Q

what is the structure of TMS

A

an Si atom bonded to 4 methyl CH3 groups in a tetrahedral shape

33
Q

deuterated solvents definition + an example

A

these are solvents where 1H atoms are replaced with 2H atoms - 2H is known as deuterium
e.g. CDCl3

34
Q

why are deuterated solvents used

A

solvents containing C or H atoms cannot be used in NMR as they would produce signals themselves
deuterated solvents produce no NMR signal in frequency ranges in H NMR and could appear at specific points in 13C NMR, so it can be ignored

35
Q

what information can be obtained from a 13C NMR spectrum

A

number of carbon environments - number of peaks
types of carbon environments - chemical shift

36
Q

what information can be obtained from a H NMR spectrum

A

number of proton environments - number of peaks
types of proton environments - chemical shift
number of neighbouring protons - splitting

37
Q

what peaks are hardest to detect on H NMR spectra + what is often added to make it easier

A

O-H or N-H peaks
this is because they can appear over a wide range of shift values

D2O is a deuterated solvent which will cause any peaks caused y O-H or N-H to be removed from the spectra, which can then be used to form a second spectra to compare to the original and determine if any OH or NH groups are present

chemistry module 6 (5 decks)

Brainscape helps you reach your goals faster, through stronger study habits.
© 2024 Bold Learning Solutions. Terms and Conditions