Question

An element has three naturally occurring isotopes of masses 23.9924, 24.9938, and 25.9898. these have abundances of 78.6%, 10.1%, and 11.3%, respectively. what is the average atomic mass of this element?

Answer 1

Answer is 24.32 amu.
Hope this helps. Thank you

Answer 2

Answer : The average atomic mass of an element is, 24.319 amu

Solution : Given,

Mass of isotope 1 = 23.9924 amu

% abundance of isotope 1 = 78.6% = 0.786

Mass of isotope 2 = 24.9938 amu

% abundance of isotope 2 = 10.1% = 0.101

Mass of isotope 3 = 25.9898  amu

% abundance of isotope 3 = 11.3% = 0.113

Formula used for average atomic mass of an element :

$\text{ Average atomic mass of an element}=\sum(\text{atomic mass of an isotopes}\times {{\text { fractional abundance}})$

$\text{ Average atomic mass of an element}=\sum[(23.9924\times0.786)+(24.9938\times 0.101)+(25.9898\times 0.113)]$

$\text{ Average atomic mass of an element}=24.319amu$

Therefore, the average atomic mass of an element is, 24.319 amu