using mass spectra

Question 1

once you’ve analysed a sample in a mass spectrometer, what can you use the mass spectrum the sample produces for?

Answer 1

to find out what’s in the sample

Question 2

how do you calculate the relative atomic mass using a mass spectra?

Answer 2

1- for each peak, read the percentage relative isotopic abundance from the y axis and the relative isotopic mass from the x axis, multiply them together to get the total relative mass for each isotope
2- add up these totals
3- divide by 100 (if percentages are used)
- if the relative abundance is not given as a percentage, the total abundance may not add up to 100, so just divide by the total relative abundance instead of 100

Question 3

what else can you get a mass spectrum for?

Answer 3

• a molecular sample

Question 4

how is a molecular M+(g) ion formed?

Answer 4

• when 1 electron is removed from the molecule
• this gives a peak in the spectrum with a mass/charge ratio equal to the Mr of the molecule
• this can then be used to identify an unknown compound
• if there’s a mixture of compounds with different Mr values, you’ll get a peak for the molecular ion of each one