The relative atomic masses of elements ... that carbon atoms have three times the mass of helium atoms. To calculate the M r for a substance: work out how many atoms of each element are in the ...

relative formula mass of H 2 = (2 × 1.0) = 2.0 Next, work out the total relative formula mass or relative atomic mass of the reactants. relative atomic mass of Zn = 65.4 relative formula mass of ...