analytical techniques II

Question 1

define isotope

Answer 1

atoms of an element w the same number of protons and different number of neutrons
-have identical chemical properties to each other

Question 2

define ionisation

Answer 2

the process whereby chemical species lose or gain an electrical charge

Question 3

define dissocation

Answer 3

the process whereby a molecule separates into smaller fragments = fragmentation

Question 4

what does a molecule need for MS

Answer 4

a POSITIVE CHARGE

Question 5

what happens in mass spectrometer

Answer 5

-electrons bombard the sample and ‘knock’ electrons off the sample, leaving it with a positive charge
-sample then accelerated through w pos charge so can be detected at detector and deflected

Question 6

what is the parent peak

Answer 6

this is the molecular ion peak = furthest to the right
the Mr of the molecule is the parent peak

Question 7

what is the base peak

Answer 7

most abundant/highest up peak

Question 8

fragmentation

Answer 8

fragmentation of the molecule is represented in the mass spectrum by peaks with a smaller m/z than the molecular ion
fragments can be produced by the breaking of almost any bond in the molecular ion

Question 9

chromatography…

Answer 9

is a technique used to separate the substances present in a mixture
also used widely to identify a substance
used mainly in mixture of organic compounds

Question 10

what is the stationary phase

Answer 10

-it is a solid or liquid the sample is applied to
-the substance ADSORBS to the stationary phase - stuck to the surface of and will not move when most strongly ADSORBED

Question 11

what is the mobile phase

Answer 11

-a liquid or gaseous phase that is passed through or over the sample
-the substance is carried along by the mobile phase depending upon degree of solubility

Question 12

thin layer chromatography principles

Answer 12

-stationary phase is plastic coated in solid material
-enables solvents that would damage paper to be used
-allows greater range of substance to be sep.
-faster
-w UV light - colourless compounds

Question 13

Rf

Answer 13

-retention factor
-higher value = greater attraction + solubility in mobile phase
-lower value = stronger adsorbance to stationary `

Question 14

Rf formula

Answer 14

distance spot moved/distance solvent moved

min=0
max=1

Question 15

Rt - GC

Answer 15

retention time is the amount of time that a sample stays in the tube. they have a greater retention time if:
-adsorb more strongly to stationary phase
-are bigger so carried more slowly by the mobile phase

Question 16

gas chromatography function

Answer 16

used for analysis of volatile, easily combustible compounds eg fuels and gases

Question 17

HPLC

Answer 17

high performance liquid chromatography
used for analysis of large molecules and compounds that cannot be easily vaporised eg. proteins, fats, vitamins
-measures retention time

Question 18

IR

Answer 18

infrared spectroscopy
helpful bc gives information about the functional groups present

Question 19

energy from infrared…

Answer 19

is not enough to promote electrons to high energy levels BUT is enough to change the vibration of the bonds in molecules
atoms in the molecule can change position due to the bending or stretching of the covalent bonds and molecule vibrations

Question 20

descriptions for IR absorption bands

Answer 20

strong, medium or weak
broad or narrow

Question 21

NMR

Answer 21

nuclear magnetic resonance
fast method of analysis
qualitative only - only structure of compound can be determined, not structures or anything
v. expensive + hazardous bc of strong magnetic field

Question 22

principles of NMR

Answer 22

the nuclei of the atoms have a property called nuclear spin - in magnetic field, they line up parallel or antiparallel to field

Question 23

what happens inside the NMR spectrometer

Answer 23

the nuclei of the atoms are usually in a low energy state and aligned with a strong magnet. a radio transmitter = provides the energy to ‘flip’ nuclei into high energy state. over time, nuclei = flip back into lower energy spin and release pulse of energy that is detected

Question 24

factors that affect retention times of components in the column

Answer 24

-length/distance of column
-molecular structure or size of molecule
-temperature of the gases over separation
-nature and chemical struc of stationary phase
-flow rate of carrier gas