MediumChemistryHigh School (11–12)Atoms and Molecules › The Mole ConceptAtoms and Molecules › Molecules, Ions and FormulaeNumericalBoard Exam
Aluminium sulfate, Al₂(SO₄)₃, is used to make water clear…
Contributed by StemPy LabTry it on paper first. A hint, the key idea and the worked solution are here when you need them.
Aluminium sulfate, , is used to make water clear. Find its formula mass, with u, u and u. Why do we call it a formula mass?
Need a reminder? The key ideaShow
One atomic mass unit, , is one twelfth of the mass of a carbon-12 atom. The average atomic mass of an element is , where is the mass of each isotope and 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
Have you tried it?
Work it out on paper first. It is fine to get stuck or make a mistake: that is how we learn. When you are ready, go through the solution one step at a time, and check each step against your own.
Step 1. Count. aluminium, sulfur and oxygen atoms.
Step 2. Add. .
Step 3. The name. It is an ionic compound of and ions, with no separate molecules, so we say formula mass.
Answer: u.
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