How many atoms of oxygen are in one formula unit of #Al_2(SO_4)3#?

1 Answer
May 10, 2016

Answer:

Well, clearly there are 12. Why?

Explanation:

#Al_2(SO_4)_3# formally derives from an aluminum trication, #Al^(3+)#, and a sulfate dianion, #SO_4^(2-)#. 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. #(2xxAl^(3+))#, and 6 negative charges #(3xxSO_4^(2-))#.

If you count up all the atoms that carry these charges, there are #(2xxAl+3xxS+3xx4xxO)#. Is this clear?

How would I form a salt from #Ca^(2+)# and phosphate anion, #PO_4^(3-)#? What composition would give electrical neutrality?