Question

A sample of naturally occurring silicon consist of si-28(27.9769amu)and silicon 30(29.9738amu). If the atomic mass of silicon is 28.0855 and the natural abundance of silicon 29 is 4.67%,what are the natural abundance of si-28 and si-30?

Answer 1

Answer:

Explanation:

Let  the  abundance  of  Si-28be  x%,  the  abundance  of  Si-30is  (1 -0.0467 -x).  The  mass  of  the sample is the weighted average of the three constituents.

28.9765*0.0467 + 27.9769*x + 29.9738*(1 -0.0467 -x) = 28.0855

=> 28.9765*0.0467 + 27.9769*x + 29.9738*0.9533 -29.9738*x = 28.0855

=> 27.9769*x -29.9738*x = 28.0855 -28.9765*0.0467 -29.9738*0.9533

=> x*-1.9969 = -1.84173

=> x = 0.92231 -x -0.0467 = 0.031The abundance of Si-28is 92.23%and the abundance of Si-30is 3.1%