Element Y has two natural isotopes Y-63 (62.940 amu) and Y-65 (64.928 amu). Calculate the atomic mass of element Y, given the abundance of Y-63 is 69.17%?

Average atomic mass = 63.553 amu.

Explanation:

Given data:

Abundance of Y-63 = 69.17%

Abundance of Y-65 = 100 - 69.17 = 30.83%

Atomic mass of Y-63 = 62.940 amu

Atomic mass of Y-65 = 64.928 amu

Atomic mass of Y = ?

Solution:

Average atomic mass= (abundance of 1st isotope × its atomic mass) +(abundance of 2nd isotope × its atomic mass)  / 100

Average atomic mass= (62.940×69.17)+(64.928×30.83) /100

Average atomic mass =  4353.560 + 2001.730 / 100

Average atomic mass = 6355.29 / 100

Average atomic mass = 63.553 amu.

the answer for sodium is 0.186

the answer for rubidium is 0.251