Relative atomic mass and relative molecular mass

Question 1

What is the relative isotopic mass?

Answer 1

The mass of an atom of an isotope compared with the mass of 1/12th an atom of 12C

This definition helps in comparing the mass of isotopes to a standard carbon isotope.

Question 2

Define relative atomic mass, Ar.

Answer 2

The weighted mean mass across all isotopes of an atom compared with 1/12th of the mass of an atom of 12C

Ar takes into account the abundance of each isotope in nature.

Question 3

What is relative molecular mass, Mr?

Answer 3

The mass of the molecule compared with 1/12th of the mass of an atom of 12C

Mr is calculated based on the sum of the atomic masses of the constituent atoms.

Question 4

How is relative molecular mass, Mr, calculated?

Answer 4

By taking the sum of the relative atomic masses of each atom in a molecule

This involves adding the Ar values of all atoms present in the molecular formula.