Question

There are two isotopes of an unknown element, X-19 and X-21. The abundance of X-19 is 12.01%. Now that you have the contribution from the X-19 isotope (2.282) and from the X-21 isotope (18.48), what is the average atomic mass (in amu) of this element using four significant figures

Answer 1

Answer: The average atomic mass of X is 16.53

Explanation:

Mass of isotope X-19  = 2.282  

% abundance of isotope X-19 = 12.01% = $\frac{12.01}{100}=0.1201$

Mass of isotope X-21 = 18.48

% abundance of isotope X-21 = (100-12.01)% = $\frac{100-12.01}{100}=0.8799$

Formula used for average atomic mass of an element :

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

$A=\sum[(2.282\times 0.1201)+(18.48\times 0.8799)]$

$A=16.53$

Therefore, the average atomic mass of X is 16.53