Isotopes and percent abundance

Question

Element A has two naturally occurring isotopes. Percent abundance for isotope A-32 is (4.18x10^1) % and mass of 32.03 amu. Second Isotope A-35 has the mass 34.98 amu. What is the atomic mass of the element A? 

Answer 1

To determine the atomic mass of Element A using the percentage abundance .The percentage abundance of isotope A is 41.8 % and it s mass is 32.03 amu. To find the percentage abundance of the second isotope A minus 100 by 41.8:

100-41.8=58.2.

After finding the percentage abundance of each isotope you calculate the atomic mass of Element A:

Average mass=(Mass of isotope)(Fractional abundance)+(Mass of isoptope)(Fractional Abundance)=(32.03)amu(0.418)+(34.98)amu(0.582)=

13.39amu+20.35amu=33.7amu

Answer 2

You may be having difficulty, because it appears they left out a piece of information, and that's the percent abundance of the other isotope. Because there are only two isotopes, they make up 100% of the abundance. If a-32 makes up 41.8%, the reamaining isotopes are A-35. Calculate that percent value by subtracting the 41.8% from 100%.

From there, use the standard method of calculating the reported mass of the element from its isotopes:

reported mass = (mass of isotope A)(abundance of isotope A) + (mass of isotope B)(abundance of isotope B) + ...

Answer 3

%A-32 = 41.8%

%A-35 = 100% - 41.8% = 58.2%

(0.418 x 32.03 ) + (0.582 x 34.98) = x

x = atomic mass of A = 13.39 + 20.36

x = 33.75 amu