Topic 7 - Analytical Techniques

Question 1

basic outline of what happens in a mass spectrometer?

Answer 1

atoms and molecules can be deflected by magnetic fields- provided the atom or molecule is first turned into an ion.
electrically charged particles are affected by a magnetic field although electrically nuetral ones aren’t.

Question 2

explain the different stages of what goes on in a mass spectrometer?

Answer 2

ionisation - atom or molecule is ionised by knocking one or more electrons off to give a positive ion.

acceleration - ions are accelerated so that they all have the same kinetic energy.

deflection- ions are then deflected by a magnetic field according to their masses.

detection- the beam of ions passing through the machine is detected eletrically

Question 3

formation of a molecular ion peak?

Answer 3

the result of the organic molecule losing an electron in the mass spectrometer.

Question 4

what is fragmentation?

Answer 4

-occurs when the molecular ion breaks into smaller pieces.

Question 5

what is the base peak?

Answer 5

-indicates the peak with the greatest abundance

Question 6

equation for how the molecular ion is formed?

Answer 6

M –> M⁺ + e⁻

Question 7

What is infrared radiation?

Answer 7

is the part of the electromagnetic spectrum with frequencies below that of red light.
Wavelengths above red light.

Question 8

What is stretching?

Answer 8

stretching occurs when a bond absorbs infrared radiation and uses it to alter the length of the bond.

Question 9

what is the transmittance value?

Answer 9

it is the value in an infrared spectrum that represents the amount of radiation absorbed at a particular wavenumber

Question 10

defintion of wavenumber?

Answer 10

the wavenumber of an infrared absorption represents the frequency of infrared radiation absorbed by a particular bond in a molecule.

Question 11

what is the intensity?

Answer 11

the intensity of an infrared absorption describes the amount of infrared radiation absorbed

Question 12

What sort of modern analytical technique is used in breath alcohol anaslyzers?

Answer 12

Infrared spectroscopy.

Question 13

what does the amount of energy absorbed depend on?

Answer 13

• the length of the bond
• the strength of the bond
• the mass of each atom involved in the bond

Question 14

why is it not easy to use infrared spectra to distinguish between propan-1-ol and propan-2-ol?

Answer 14

The bonds in propan-1-ol and propan-2-ol are the same – they are C–C, C–H, C–O and O–H, so the absorptions are very similar.

Question 15

what is meant by refluxed?

Answer 15

continous evaporation and condensing of the reactant liquid.

Question 16

Explain why hydrogen fluoride absorbs infrared radiation but fluorine does not?

Answer 16

Only polar molecules absorb infrared radiation. Hydrogen fluoride contains a polar H–F bond and so absorbs,
but the bond in fluorine (F–F) is not polar so does not absorb.