Relative Mass

Question 1

Significance of carbon 12

Answer 1

Mass of carbon 12 isotope defined as exactly 12 atomic mass units
Standard mass for atomic mass is the mass of 1/12 of carbon 12 atom

Question 2

Relative isotopic mass

Answer 2

Mass of an isotopic relative to 1/12th of the mass of a carbon 12 atom

Question 3

Relative atomic mass

Answer 3

Weighed mean mass of an atom of element relative to 1/12th mass of carbon 12
Takes into account, percentage abundance of each isotope, relative isotopic mass of each isotope

Question 4

Determination of relative atomic mass

Answer 4

Mass spectrometer gives % abundance
Sample vaporised, ionised to form cations
Ions accelerated, heavy ions move more slowly, harder to deflect than lighter ions
Ions detected on mass spectrum as mass/charge ratio

Question 5

How to calculate % abundance?

Answer 5

Peak height/ total height of all peaks x 100

Question 6

How to calculate RAM?

Answer 6

Mass x %

100

Question 7

Determination of relative isotopic mass

Answer 7

Mass spectrometer can record accurate m/z ratio for each isotope so accurate values of RIM can be measured