posted by annabel .
A sample of iron ore contains 1.02 x 10^24
Fe atoms and is found to be 69.94% Fe by mass. What is
the mass of the sample?
mols Fe = 1.02E24/6.02E23.
g Fe = mols Fe x atomic mass Fe.
%Fe = (g Fe/mass sample)*100
You have g Fe and %Fe, solve for mass sample.