What is the average atomic mass of silicon?

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What is the average atomic mass of silicon?

The isotopic distribution of the silicon element is $92.2 %$ $92.2%$ $^{28} S i$ $""^28Si$ $(mass of the isotope is 27.968 amu)$ $("mass of the isotope is 27.968 amu")$ , $3.1 %$ $3.1%$ $^{30} S i$ $""^30Si$ $(mass of the isotope is 29.9737 amu)$ $("mass of the isotope is 29.9737 amu")$ , and $3.1 %$ $3.1%$ $^{29} S i$ $""^29Si$ $(mass of the isotope is 28.9765 amu)$ $("mass of the isotope is 28.9765 amu")$ .

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Answer 1 · 2016-09-07T04:01:26

$^{29} S i$ $""^29Si$ and $^{30} S i$ $""^30Si$ have been multiplied by the wrong scaling factor.

Explanation:

$27.9768 \times 92.2 % + 28.9765 \times 4.68 % + 29.9737 \times 3.10 %$ $27.9768xx92.2%+28.9765xx4.68%+29.9737xx3.10%$ $=$ $=$ $27.9768 \times 0.922 + 28.9765 \times 0.0468 + 29.9737 \times 0.0310$ $27.9768xx0.922+28.9765xx0.0468+29.9737xx0.0310$ $=$ $=$ $28.0800$ $28.0800$ $amu$ $"amu"$ .

i.e. $1 %$ $1%$ $=$ $=$ $(0.01)$ $(0.01)$ or $(\frac{1}{100}) \times the original quantity$ $(1/100)xx"the original quantity"$

It's all too easy to make a mistake with 'rithmetic! We have all done it.

The atomic mass of $S i$ $Si$ that appears on the Periodic Table is $28.0855$ $28.0855$ $amu \pm 0.0003$ $"amu" ± 0.0003$ , so we are within error. Good luck in your exam.

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What is the average atomic mass of silicon?

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