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Gallium has two isotopes: gallium-69 of mass 68.926 u and gallium-71 of mass 70.925 u.

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Gallium has two isotopes: gallium-69 of mass $68.926$ u and gallium-71 of mass $70.925$ u. Its average atomic mass is $69.72$ u. What percentage of gallium atoms are gallium-69?

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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← Silicon has three isotopes: silicon-28 of mass 27.977 u (92.23%), silicon-29 of mass 28.976 u…Aluminium sulfate, Al₂(SO₄)₃, is used to make water clear. →

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Gallium has two isotopes: gallium-69 of mass 68.926 u and gallium-71 of mass 70.925 u.

The worked solution

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