How many atoms of oxygen are in one formula unit of Al2(SO4)3?

1 Answer
May 10, 2016

Well, clearly there are 12. Why?

Explanation:

Al2(SO4)3 formally derives from an aluminum trication, Al3+, and a sulfate dianion, SO24. Now ionic substances form to balance charges, and the only way to achieve neutrality for these net charges is to take 6 positive charges, i.e. (2×Al3+), and 6 negative charges (3×SO24).

If you count up all the atoms that carry these charges, there are (2×Al+3×S+3×4×O). Is this clear?

How would I form a salt from Ca2+ and phosphate anion, PO34? What composition would give electrical neutrality?