An average sample of chlorine contains 75.77% chlorine-35, with an atomic mass of 34.969 amu (atomic mass units), and 24.23% chlorine-37, with an atomic mass of 36.966 amu. What is the average atomic mass of chlorine?

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Answer 1 · 2015-12-06T08:53:27

You require the weighted average.

The weighted average is the sum of each individual nuclide, multiplied by its isotopic abundance.

So, we simply do the arithmetic:

#0.7577xx34.969+0.2423xx36.966 = ???# amu

Then look at the Periodic Table to see how accurate your result is.