Question

The mass numbers of three isotopes of an element are 10, 12, and 14 units. Their percentage abundance is 80, 15 and 5, respectively. What is the atomic weight of the element?

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Answer 1

Now, what is average weight?

Average weight = $\frac{\%abundance\times Massnumber}{Totalofration}$

Now,

The percentage abundance of isotopes is 80 , 15 and 5.

Thus their ratio is 16:3:1

Total of the ration = 16 + 3 + 1 =20

Average weight = $\frac{\%abundance\times Massnumber}{Totalofration}$

$\therefore Averageweight=\frac{10\times 16+12\times 3+14\times 1}{20}=10.5$

Thus, the aveage atomic weight is 10.5 units.