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Chemistry > Analytical Chemistry > Flashcards

Analytical Chemistry Flashcards

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1
Q

definition of partition coefficient

A

equilibrium constant that relates the concentration of solute between two immiscible solvents

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2
Q

definition of adsorption

A

bonding of molecules to surface of stationary phase

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3
Q

definition of paper chromatography

A

components partition between solvent and liquid stationary phase

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4
Q

solvent and stationary phase of paper chrom.

A 
mobile phase (liquid/gas)
water trapped in cellulose fibres
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5
Q

describe paper chrom. with non polar solvent

A

little attraction to -OH groups on cellulose

high Rf value

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6
Q

describe paper chrom. with polar solvent

A

dissolve more in stationary phase

low Rf value

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7
Q

how to identify colourless substances

A

ninhydrin spray

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8
Q

describe two way chromatography

A

Rotate 90 degrees

Re run in a different solvent

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9
Q

definition of thin layer chromatography

A

Separation depends on the differential adsorption of components onto the solid phase (Al2O3/SiO2)

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10
Q

solvent and stationary phase of thin layer chrom.

A

mobile phase

Al2O3/SiO2

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11
Q

thin layer chrom in very polar solvent

A

dissolves more in solvent = high Rf value

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12
Q

what compounds that can hydrogen bond do

A

adsorb more to solid stationary phase

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13
Q

definition of high performance liquid chromatography

A

using partition to separate

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14
Q

describe high performance liquid chrom.

A

non volatile liquid( hydrocarbon) on solid support (silica) = stationary phase

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15
Q

mobile phase of HPLC

A

polar solvent

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16
Q

what does the detector on HPLC record

A

retention time= time it takes for component to pass column

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17
Q

what does area under peak show in HPLC

A

amount of solute out of column

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18
Q

what is HPLC used for

A

Separate peptides and proteins
Analyse urine samples
Monitoring pollutants

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19
Q

describe gas liquid chromatography

A

similar to HPLC but gaseous sample

20
Q

conditions for gas liquid chrom.

A

same inert carrier gas
flow rate
stationary phase
temperature

21
Q

limitation of gas liquid chrom.

A

similar compounds will have similar retention times - new compounds wont have match

22
Q

how to find percentage composition of mixture by GLC

A

1/2 x base x height

23
Q

what is GLC used for

A

Testing steroids in athletes
Testing fuels used in racing
Analysing blood samples

24
Q

how does a GLC graph look like

A

recorder response/time

25
Q

purpose of NMR

A

Used to identify hydrogen atoms in different part of the molecule

26
Q

how does NMR work

A

nuclear spin from spinning proton produces two spin states
energy absorbed in NMR
can align with or against applied field

27
Q

why is TMS used as standard reference compound

A

inert volatile liquid
equivalent hydrogen atom environments
one sharp peak
12 protons in same environment = high frequency

28
Q

how to find -OH-/-NH- in NMR spectrum

A

Produce an NMR
Add D2O (doesn’t absorb electromagnetic spectrum, no protons) sample
Rerun NMR
Compare to find the peak that has disappeared = OH/NH peak

29
Q

why is -OH-/-NH- appear to be a single peak

A

reacts quickly with water

30
Q

reaction of -OH- with D2O

A

OH + D2O ⇌ -OD + HOD

31
Q

reaction of -NH-CO- and D2O

A

⇌ -ND-CO- + HOD

32
Q

what does low resolution NMR show

A

single peaks for different environment of hydrogen

33
Q

what does high resolution NMR show

A

cluster of peaks for each environment and neighbouring hydrogens

34
Q

how do find neighbouring hydrogens

A

splitting peaks -1

35
Q

what does height of peak show

A

number of hydrogen

36
Q

what does more down field peak show

A

closer to electronegative element

37
Q

describe carbon-13 NMR spectrometry

A

1% of carbons in compound will be carbon-13 instead of carbon-12
CDCl3 solvent used to prepare sample

38
Q

formula for double bonds

A

2n+2 -#H/2

39
Q

definition of mass spectrometry

A

Mass spectrometry of an element can be used to measure relative isotopic masses and their relative abundances = calculate relative atomic masses

40
Q

process of mass spectrometry

A

Sample is vaporised
Sample bombarded with high energy electrons
Breaks covalent bonds by fragmentation

41
Q

how are compounds fragmented

A

primary < secondary < tertiary

42
Q

where is the molecular mass found in mass spectrometry

A

last peak

43
Q

how to find number of carbons using [m+1] peak

A

(100/1.1) x ([M+1]+1)/M+

44
Q

percentage of [M+2] and [M] in Cl

A 
35Cl = 75%
37Cl = 25%
45
Q

percentage of [M+2] and [M] in Br

A 
79Br = 50%
81Br = 50%
46
Q

when there is two Cl/Br in compound

[M]:[M+2]:[M+4]

A

two Cl atoms: three peaks with 9:6:1 ratio

two Br atoms: three peaks with 1:2:1 ratio

Chemistry (15 decks)

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