Average Atomic Mass: Chemistry

Question

An element consists of four isotopes with the following natural abundances:



               Natural Abundance (%) Atomic Mass (amu)
isotope 1                18.952                134.400
isotope 2                15.778                135.391
isotope 3                23.491                137.373
isotope 4                41.779                     ?


If the average atomic mass of the element is 137.325 amu, calculate the isotopic mass of the fourth isotope.

 

(Report your answer to three decimal places.)

Answer 1

(.18952)(134.400) = 25.4715

(.15778)(135.391) = 21.3620

(.23491)(137.373) = 32.2703

(.41779)(x)           = .41779x

add these:               79.1038 + .41779x = 137.325

.41779x = 58.2212

x = 139.355