Indium has two naturally occurring isotopes and an atomic mass of 114.818 amu. In- 113 has a mass of 112.904 amu and an abundance of 4.3%. What is the identity and percent abundance of indium's other isotope. I am very confused on how do I set up this conversion problem?

Question

Indium has two naturally occurring isotopes and an atomic mass of 114.818 amu. In- 113 has a mass of 112.904 amu and an abundance of 4.3%. What is the identity and percent abundance of indium's other isotope.  I am very confused on how do I set up this conversion problem?

DrBob222 · Accepted Answer

atomic masses are weighted averages of all of the isotopes.
% in 113 = 4.3% and since the isotopes must add to 100%, then 100 - 4.3 = 95.7% for the other isotope.
Let x = to mass of the other isotope. Then set up the average.

112.904(0.043) + (x)(0.957) = 114.818 and solve for x.
95&% is part of the answer. x is the other part of the question. Check my numbers against typos. I make a typo now and then.

Jess · Answer

5.07301149