Question

What is the correct numerical set up for calculating the atomic mass of Si

Answer 1

Answer:

You determine the weighted averages if the individual isotopic masses.

Procedure:

The atomic mass of Si is the weighted average of the atomic masses of its isotopes.

We multiply the atomic mass of each isotope by a number representing its relative importance (i.e., its percent abundance).

The three stable isotopes of Si are Si-28 (27.98 u, 92.22 %), Si-29 (28.98 u, 4.69 %), and Si-30 (29.97 u, 3.09 %).

Set up a table for easy calculation.

0.9222 × 27.89 u = x u

0.0469 × 28.98 u = y u

0.0309 × 29.97 u = z u

         TOTAL =  (x+y+z) u = atomic mass of Si.