Isotopic Abundance ( formula in the book does not work)?

Question

Hydrogen is found primarily as two isotopes in nature: H1 (1.0078u) and H2( 2.0140u) Calculate the percentage abudnace of each isoptope based on hydrogen's average mass. How would i do this.

Answer 1

Let percentage of H1 be "x" and that of H2 be (100-X)
As the average mass of hydrogen is 1.0079u,therefore,

( X*1.0078+ (100-X) *2.0140 ) /100=1.0079;

or 1.0078X+201.40-2.0140X =1.0079 *100;

or -1.0062 X = 100.79-201.40;

or -1.0062X = - 100.61;

or X = 100.61/1.0062;

or X = 99.99 %;
Therefore,H1 is 99.99% and H2 is 0.01%

Answer 2

to calculate for the % abundance
let ,H1=1-x
H2=x
average of H=1.5109
1.5109=1.0078(x-1)+2.0140(x)
1.5109-1.0078=1.0078x+2.0140x
0.5031=3.0218x
x=0.16649x100=16.649%
1-x=0.88351x100=88.351%
*the answer is inaccurate because the average of the the mass of an element is not "the atomic mass." some elements have atomic masses similar to the atomic mass on the periodic table.
Find the actual atomic mass for H and follow the procedure.

Answer 3

1. find out the most accurate Ar value that you can for H. Then solve:
2. (y x 1.0078) + (z x 2.014) = Ar and y + z = 1
3. multiply y and z by 100 to get percentages.