Calculate the atomic mass of silicon. the three silicon isotopes have the following atomic masses and % .9769 amu and 92.2297%), (29.9765 amu and 4.6832%), (29.9738 amu and 3.0872%)

The calculated atomic mass of silicon is 28.104 u.

The average 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 % abundance).  

Thus,  

0.922 97    × 27.9769 u = 25.821 8      u

0.046 832 × 28.9765 u =   1.357 03    u

0.030 872 × 29.9738 u =   0.925 351 u

                         TOTAL = 28.104         u

Note: Your percentages don’t add up to 100.0000 % (I think the first one is incorrect).

explanation:

two years ago, when picking flowers in the mountains back of yosemite valley, i found a book. it was blotted and storm-beaten; all of its outer pages were mealy and crumbly. the paper seemed to dissolve like the snow beneath which it had been buried, however; many of the inner pages were well preserved. and although all were more or less stained and torn, whole chapters were easily readable. this is the condition of the great open book of yosemite glaciers today; its granite pages have been torn and blurred by the same storms that wasted the castaway book.

two years ago, when picking flowers in the mountains back of yosemite valley; i found a book. it was blotted and storm-beaten, all of its outer pages were mealy and crumbly. the paper seemed to dissolve like the snow beneath which it had been buried, however, many of the inner pages were well preserved. and although all were more or less stained and torn; whole chapters were easily readable. this is the condition of the great open book of yosemite glaciers today, its granite pages have been torn and blurred by the same storms that wasted the castaway book.