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Silicon has three isotopes: silicon-28 of mass 27.977 u (92.23%), silicon-29 of mass 28.976 u…

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Silicon has three isotopes: silicon-28 of mass $27.977$ u ( $92.23\%$ ), silicon-29 of mass $28.976$ u ( $4.67\%$ ) and silicon-30 of mass $29.974$ u ( $3.10\%$ ). Find the average atomic mass of silicon.

Need a reminder? The key ideaShow

One atomic mass unit, $1\ \text{u}$ , is one twelfth of the mass of a carbon-12 atom. The average atomic mass of an element is $\bar{A} = \dfrac{\sum m_i p_i}{100}$ , where $m_i$ is the mass of each isotope and $p_i$ its share in percent. The molecular mass, or the formula mass of an ionic compound, is the sum of the atomic masses of all the atoms in the formula.

The worked solution

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← Urea, CO(NH₂)₂, is a fertiliser. Find its molecular mass, with C = 12.01 u, O = 16.00 u, N = 14.01…Gallium has two isotopes: gallium-69 of mass 68.926 u and gallium-71 of mass 70.925 u. →

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Silicon has three isotopes: silicon-28 of mass 27.977 u (92.23%), silicon-29 of mass 28.976 u…

The worked solution

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