What is the average atomic mass of silicon?

Question

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")#.

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Answer 1 · 2016-09-07T04:01:26

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

#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.