A new compound was recently discovered and found to have an atomic weight of 342.38 amu.This element has two isotopes,the lighter of which has a mass of 340.91 amu and an abundance of 68.322%.What is the mass of the heavier isotope?
A) 350.21
B) 345.55
C) 342.38
D) 348.67
E) 343.29

Question

Quizplus · Accepted Answer

Let x be the abundance of the heavier isotope.
Then we have:

(0.68322)(340.91) + (x)(m) = 342.38

where m is the mass of the heavier isotope.
Solving for m, we get:

m = (342.38 - 0.68322(340.91)) / x
m ≈ 345.55

Therefore, the mass of the heavier isotope is approximately 345.55 amu, which is closest to choice B).

A New Compound Was Recently Discovered and Found to Have