Question

An element has two naturally-occurring isotopes. The mass numbers of these isotopes are 113 amu and 115 amu, with natural abundances of 5% and 95%, respectively. Calculate its average atomic mass. Report your answer to 1 decimal place.

Answer 1

Answer: Its average atomic mass is 114.9 amu

Step-by-step explanation:

Mass of isotope 1 = 113 amu

% abundance of isotope 1 = 5% =
`(5)/(100)=0.05`

Mass of isotope 2 = 115 amu

% abundance of isotope 2 = 95% =
`(95)/(100)=0.95`

Formula used for average atomic mass of an element :

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

`A=\sum[(113* 0.05)+(115* 0.95)]`

`A=114.9amu`

Thus its average atomic mass is 114.9 amu