3. relative mass

Question 1

definition

relative atomic mass Ar

Answer 1

the weighted mean mass of an atom of an element compared to 1/12th of the mass of an atom of carbon-12

Question 2

definition

relative isotopic mass

Answer 2

the mass of an atom of an isotope

compared with 1/12th of the mass of an atom of carbon-12

Question 3

how to work out relative molecular mass (mr) / relative formula mass

Answer 3

add up relative atomic mass values of all atoms in molecule

Question 4

what is the difference between relative molecular mass (mr) and relative formula mass?

Answer 4

relative atomic mass used when referring to simple molecules
relative formula mass used for compounds that are ionic or giant covalent e.g. SiO2

Question 5

how to work out mr from relative isotopic abundances

2 steps

Answer 5

1. relative isotopic mass x % relative isotopic abundance
   (add up all results)
2. divide by 100.

Question 6

how to work out mr from mass spectra

2 steps

Answer 6

1. relative isotopic mass x relative isotopic abundance

2. divide by sum of all isotopic abundances