What is the average atomic mass of silicon?

The isotopic distribution of the silicon element is 92.2% ""^28Si ("mass of the isotope is 27.968 amu"), 3.1% ""^30Si ("mass of the isotope is 29.9737 amu"), and 3.1% ""^29Si ("mass of the isotope is 28.9765 amu").

1 Answer
Sep 7, 2016

""^29Si and ""^30Si have been multiplied by the wrong scaling factor.

Explanation:

27.9768xx92.2%+28.9765xx4.68%+29.9737xx3.10% = 27.9768xx0.922+28.9765xx0.0468+29.9737xx0.0310 = 28.0800 "amu".

i.e. 1% = (0.01) or (1/100)xx"the original quantity"

It's all too easy to make a mistake with 'rithmetic! We have all done it.

The atomic mass of Si that appears on the Periodic Table is 28.0855 "amu" ± 0.0003, so we are within error. Good luck in your exam.