Experimental Determination of Structure (U2, c5/6)

Question 1

1) What happens to a ~2mg sample in a combustion analyser during elemental microanalysis?
2) What does this produce?
3) What is then measured?

Answer 1

1) It is oxidised at a high temperature in an atmosphere of oxygen.
2) This produces a mixture of gases - SO2, N2, CO2 and H2O.
3) The mass of each gas component

Question 2

How are gases separated in Elemental Microanalysis?

Answer 2

By gas chromatography.

Question 3

How is the mass of each gaseous component measured in Elemental Microanalysis?

Answer 3

By using a thermal conductivity detector.

Question 4

In Elemental Microanalysis, how can the empirical formula be calculated from the masses of each product gas?

Answer 4

1) The gas masses are converted into masses of the original element (SO2 to S, etc.) by considering molar quantities.
2) These values are all subtracted from the original mass of the sample. This gives the mass of oxygen in the initial sample.
3) The empirical formula can be calculated from these element masses using molar ratios. :)

Question 5

What is Elemental Microanalysis used to determine?

Answer 5

The masses of C, H, O, S and N in a sample of an organic compound to determine its imperial formula.

Question 6

What is Mass Spectrometry used to determine?

Answer 6

The accurate molecular mass and structural features of an organic compound.

Question 7

What is IR Spectroscopy used to identify & work out?

Answer 7

Identify certain functional groups and work out which compound is responsible for a spectra (by identifying which functional groups are for peaks).

Question 8

What two pieces of information can Proton Nuclear Magnetic Resonance (NMR) give us?

Answer 8

Information about:

1) The different environments of H atoms in an organic molecule, and
2) How many H atoms there are in each environment.