Analytical Chemistry

Question 1

definition of partition coefficient

Answer 1

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

Question 2

definition of adsorption

Answer 2

bonding of molecules to surface of stationary phase

Question 3

definition of paper chromatography

Answer 3

components partition between solvent and liquid stationary phase

Question 4

solvent and stationary phase of paper chrom.

Answer 4

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

Question 5

describe paper chrom. with non polar solvent

Answer 5

little attraction to -OH groups on cellulose

high Rf value

Question 6

describe paper chrom. with polar solvent

Answer 6

dissolve more in stationary phase

low Rf value

Question 7

how to identify colourless substances

Answer 7

ninhydrin spray

Question 8

describe two way chromatography

Answer 8

Rotate 90 degrees

Re run in a different solvent

Question 9

definition of thin layer chromatography

Answer 9

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

Question 10

solvent and stationary phase of thin layer chrom.

Answer 10

mobile phase

Al2O3/SiO2

Question 11

thin layer chrom in very polar solvent

Answer 11

dissolves more in solvent = high Rf value

Question 12

what compounds that can hydrogen bond do

Answer 12

adsorb more to solid stationary phase

Question 13

definition of high performance liquid chromatography

Answer 13

using partition to separate

Question 14

describe high performance liquid chrom.

Answer 14

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

Question 15

mobile phase of HPLC

Answer 15

polar solvent

Question 16

what does the detector on HPLC record

Answer 16

retention time= time it takes for component to pass column

Question 17

what does area under peak show in HPLC

Answer 17

amount of solute out of column

Question 18

what is HPLC used for

Answer 18

Separate peptides and proteins
Analyse urine samples
Monitoring pollutants

Question 19

describe gas liquid chromatography

Answer 19

similar to HPLC but gaseous sample

Question 20

conditions for gas liquid chrom.

Answer 20

same inert carrier gas
flow rate
stationary phase
temperature

Question 21

limitation of gas liquid chrom.

Answer 21

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

Question 22

how to find percentage composition of mixture by GLC

Answer 22

1/2 x base x height

Question 23

what is GLC used for

Answer 23

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

Question 24

how does a GLC graph look like

Answer 24

recorder response/time

Question 25

purpose of NMR

Answer 25

Used to identify hydrogen atoms in different part of the molecule

Question 26

how does NMR work

Answer 26

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

Question 27

why is TMS used as standard reference compound

Answer 27

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

Question 28

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

Answer 28

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

Question 29

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

Answer 29

reacts quickly with water

Question 30

reaction of -OH- with D2O

Answer 30

OH + D2O ⇌ -OD + HOD

Question 31

reaction of -NH-CO- and D2O

Answer 31

⇌ -ND-CO- + HOD

Question 32

what does low resolution NMR show

Answer 32

single peaks for different environment of hydrogen

Question 33

what does high resolution NMR show

Answer 33

cluster of peaks for each environment and neighbouring hydrogens

Question 34

how do find neighbouring hydrogens

Answer 34

splitting peaks -1

Question 35

what does height of peak show

Answer 35

number of hydrogen

Question 36

what does more down field peak show

Answer 36

closer to electronegative element

Question 37

describe carbon-13 NMR spectrometry

Answer 37

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

Question 38

formula for double bonds

Answer 38

2n+2 -#H/2

Question 39

definition of mass spectrometry

Answer 39

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

Question 40

process of mass spectrometry

Answer 40

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

Question 41

how are compounds fragmented

Answer 41

primary < secondary < tertiary

Question 42

where is the molecular mass found in mass spectrometry

Answer 42

last peak

Question 43

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

Answer 43

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

Question 44

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

Answer 44

``` 35Cl = 75% 37Cl = 25% ```

Question 45

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

Answer 45

``` 79Br = 50% 81Br = 50% ```

Question 46

when there is two Cl/Br in compound | [M]:[M+2]:[M+4]

Answer 46

two Cl atoms: three peaks with 9:6:1 ratio | two Br atoms: three peaks with 1:2:1 ratio