The average atomic mass of a sample of an element X is 16.2 u. What are the percentages of isotopes and in the sample?
Percentage of + = 100%
Let the percentage of be X%
And the percentage of be 100 - X%
We know the average atomic mass of a sample of an element X is 16.2 u.
Average mass of an isotope = (% existence of the isotope 1 x mass of isotope 1) +
(% existence of the isotope 2 x mass of isotope 2)
(Mass of x X%) + [Mass of x (100-X%)] = 16.2
[16 x (X/100)] + [18 x ( (100-X) /100 )] = 16.2
[16X] + [18 x (100 - X)] = 1620
[16X] + [1800 - (18X)] = 1620
1800 - 2X = 1620
2X = 180
X = 90
-> X = 90% and 100-X = 10%
That means 90% of and 10% of is present.