Tricky molar mass question!

The element Gallium has two isotopes:

Ga 31 Protons, Molar mass 69
Ga 31 Protons, Molar mass 71

The molar mass of a sample of gallium is 69.8g mol-1
Calculate the percentage abundance of the isotope Ga Proton Number 31, Atomic number 69 in the sample.

To work out molar mass you multiply percentage abundance by molar mass and then divide by 100. I can’t see how you can work out the percentage abundance from this data. :confused:

Could anybody tell me how you can do this question? :confused:

Reply 1

charco

Study Forum Helper

you have to use algebra

let the % of 69Ga be y%
the % of 71Ga is 100-y%

now apply the formula

RAM = {(y x 69) + [(100-y) x 71]}/100

69.8 x 100 = 69y + 7100 - 71y

7100 - 6980 = 2y

y = 60% therefore 100 - y = 40%