Question

Calculate the atomic mass of silicon. The three silicon isotopes have atomic masses and relative abundances of 27.9769 amu (92.2297%), 28.9765 amu (4.6832%) and 29.9738 amu (3.0872%). Show your work.

Answer 1

Converting the percent abundance into decimal form, we get:

Si-28: 92.21% = 92.21/100 = 0.9221

Si-29: 4.70% = 4.70/100 = 0.0470

Si-30: 3.09% = 3.09/100 = 0.0309

Average atomic mass of silicon is:

(27.98) x (0.9221) + (28.98) x (0.0470) + (29.97) x (0.0309)

= 25.800 + 1.362 + 0.926

= 28.08 amu

Step-by-step explanation:

From PLATO

Answer 2

The atomic mass would be 28.08535 amu. Multiply 27.9769 by .92297 = 25.803. Multiply 28.9765 by .046832 to get 1.357. Multiply 29.9738 by .03872 to get .925351136. Add 25.803 + 1.357 + .03872 to get 28.08535 amu