experimental determination of structure 1

Question 1

what is elemental microanalysis used for

Answer 1

used to determine the empirical formula of an organic compound
- used to determine the masses of C, H, O, S and N in a sample of an organic compound in order to determine its empirical formula.

Question 2

An empirical formula shows….

Answer 2

… the simplest ratio of the elements in a molecule.

Question 3

elemental microanalysis

• how is it then calculated
• how is mass of oxygen calculated

Answer 3

• small compound of a sample which may contain, C, H , N , S ,(approx 2mg) is weighed accurately
• it is oxidised at a high temp in an atmosphere of pure oxygen
• depending on the compound under analysis , this will produce a mixture of gases , N2, SO2,,CO2,H20
• these gases are separated by gas chromatography
• the mass of each component of combustion is then measured using a thermal conductivity detector

( by converting the mass of each product gas into the mass of the original element , the masses of C ,H ,N,S, can be determined by simple calculation.
if oxygen is present then its mass is given by subtracting each of the masses from the original mass of the sample)

Question 4

elemental microanalysis calculations

Answer 4

notes

Question 5

what is mass spectrometry

Answer 5

a technique used to determine the accurate molecular mass and structural features of an organic compound

Question 6

how is mass spectroscopy carried out

Answer 6

• sample of organic compound is bombarded by high energy electrons
• knocks out electrons from the molecule, forming positively charged ion fragments
• magnetic field deflects the ions
• deflected ions are received by a detector and a computer converts them into a mass spectrum
• this results in a spectrum being produced which consists of several lines from both the original molecule and the molecular ion fragments

Question 7

what is the line with the largest mass/charge ratio (furthest to right)

Answer 7

• the line of the molecular ion , a molecule which has lost one electron- provides the gfm of the organic compound

Question 8

positive ions with lower mass/charge ratios are deflected ____ than those with higher ratios

Answer 8

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