posted by Luc on .
An element with relative atomic mass 20.8 is found to contain 2 isotopes having a relative atomic mass of 20 and 21.Find the % composition of the element.
Relative atomic mass = 20.8 g
Let the fraction that is element 20 = x
thus the fraction that is element 21=1-x
so 20x +21(1-x) = 20.8
20x + 21 -21x=20.8
x=0.2 and 1-x=0.8
so 20% element 20 and 80% element 21.