Question

Magnesium has three naturally occurring isotopes: Mg-24 with mass 24.3050 amu and a natural abundance of 78.99 %, Mg-25 with mass 24.9858 amu and a natural abundance of 10.00 %, and Mg-26 with mass 25.9826 amu and a natural abundance of 11.01 %.

Answer 1

we know that

average atomic mass = ( mass of isotope A x % abundance + mass of isotope B x % abundance + -------) / 100

given

mass of isotop Mg-24 = 24.3050

% abundance of Mg-24 = 78.99

mass of isotope Mg-25 = 24.9858

% abundance of Mg-25 = 10

mass of isotope Mg-26 = 25..9826

% abundance = 11.01

so

the average atomic mass is given by

average atomic mass = ( 24.2050 x 78.99 + 24.9858 x 10 + 25.9826 x 11.01) / 100

average atomic mass = 2447.879376 / 100

average atomic mass = 24.4788

so

the average atomic mass of magnesium is 24.4788 amu