Question

A newly discovered element, Y, has two naturally occurring isotopes. 90.3 percent of the sample is an isotope with a mass of 267.8 u, and 9.7 percent of the sample is an isotope with a mass of 270.9 u. What is the weighted average atomic mass for this element? 269.4 u 268.1 u 269.0 u 270.6 u

Answer 1

Answer: 268.1 u

Explanation:

Mass of isotope 1 = 267.8 u

% abundance of isotope 1 = 90.3% = $\frac{90.3}{100}=0.903$

Mass of isotope 2 = 270.9 u

% abundance of isotope 2 = 9.7% = $\frac{9.7}{100}=0.097$

Formula used for average atomic mass of an element :

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

$A=\sum[267.8\times 0.903+270.9\times 0.097]$

$A=268.1u$

Therefore, the average atomic mass of an element is, 268.1 u

Answer 2

268.1u is your answer.