2.4 — determination of relative mass

Question 1

what does a mass spectrum plot?

Answer 1

the relative abundance of ions against their mass-to-charge ratio (m/z)

Question 2

what does the x axis on a mass spectra display?

Answer 2

the m/z values

Question 3

what does the m/z of each peak equal?

Answer 3

the relative mass of the ion

Question 4

what does the y axis on a mass spectra indicate?

Answer 4

the relative abundance of each ion

Question 5

what are the forms of relative abundance being presented on mass spectra?

Answer 5

arbitrary units or a percentage

Question 6

what does each peak on a mass spectra represent for elemental samples?

Answer 6

a different isotope

Question 7

for elemental samples, what does relative height of each peak show?

Answer 7

the isotopes abundance

Question 8

what does a single peak for elemental samples show?

Answer 8

that it contains one stable isotope

Question 9

for molecular samples, what is the peak at the highest m/z value?

Answer 9

the molecular ion (M⁺)

Question 10

what does the m/z of the molecular ion peak match?

Answer 10

the molecule’s relative molecular mass (M_r)

Question 11

where do peaks at lower m/z values come from?

Answer 11

fragments of the molecular ion

Question 12

how can an element’s relative atomic mass (A_r) be found from its mass spectrum?

Answer 12

1. multiply the relative atomic mass by its relative abundance for each isotope
2. add these products together
3. divide the total by the sum of the relative abundances (100 if using percentages)