Question

What is the average isotopic mass of an element that has the following abundances in nature? Isotopic mass: X20 X22 X23 Abundances in natures: 90.5 % 8.0 % 1.5 %

Answer 1

Answer: 20.2

Explanation:

Mass of isotope 1 = 20

% abundance of isotope 1 = 90.5% = $\frac{90.5}{100}=0.905$

Mass of isotope 2 = 22

% abundance of isotope 2 = 8.0% = $\frac{8}{100}=0.08$

Mass of isotope 3 = 23

% abundance of isotope 3 = 1.5% = $\frac{1.5}{100}=0.015$

Formula used for average atomic mass of an element :

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

$A=\sum[(20\times 0.905+(22\times 0.08)+(23\times 0.015]$

$A=20.2$

Therefore, the average atomic mass of the element is 20.2.