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

268.1u is your answer. 

Answer 2

Answer: 268.1 u

Step-by-step explanation:

Mass of isotope 1 = 267.8 u

% abundance of isotope 1 = 90.3% =
`(90.3)/(100)=0.903`

Mass of isotope 2 = 270.9 u

% abundance of isotope 2 = 9.7% =
`(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}* {{\text { fractional abundance}})`

`A=\sum[267.8* 0.903+270.9* 0.097]`

`A=268.1u`

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