Magnesium has three natural isotopes. 78.70% of the magnesium atoms exist as Mg-24, 10.03% exist as Mg-25, and 11.17% exist as Mg-26. What is the average atomic mass of magnesium?

Average atomic mass = 24.29 amu.

Explanation:

Given data;

Abundance of Mg-24 = 78.70%

Abundance of Mg-25= 10.03%

Atomic mass of Mg-26 = 11.17%

Average atomic mass = ?

Solution:

Average atomic mass = (abundance of 1st isotope × its atomic mass) +(abundance of 2nd isotope × its atomic mass) +(abundance of 3rd isotope × its atomic mass)  / 100

Average atomic mass = (78.70×24)+(10.03×25)+(11.17×26) /100

Average atomic mass =  1888.8 + 250.75 +290.42 / 100

Average atomic mass = 2429.97 / 100

Average atomic mass = 24.29 amu.