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Aluminium sulfate, Al₂(SO₄)₃, is used to make water clear.

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Aluminium sulfate, $\text{Al}_2(\text{SO}_4)_3$ , is used to make water clear. Find its formula mass, with $\text{Al} = 26.98$ u, $\text{S} = 32.07$ u and $\text{O} = 16.00$ u. Why do we call it a formula mass?

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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Aluminium sulfate, Al₂(SO₄)₃, is used to make water clear.

The worked solution

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