Question

3Ca(CH3COO)2(aq) + 2H3PO4(aq) ¨ Ca3(PO4)2(aq) + 6CH3COOH (aq)

reduce in net ionic form... how do you know what to separate? for example, how would i know to separate Ca and PO4 or to keep it together??

Answer 1

You have to be careful how you write the equations, because it makes a big difference. Shouldn't the aq after the calcium phosphate be (s)? Calcium phosphate is not very soluble, as I recall. If in fact it does form a precipate, then you have a chemical reaction.

Ca++(aq) + 2(PO4==)(aq) >> Ca3(PO4)2 (s)

Answer 2

nope, the equation given is all aqueous.

Answer 3

If it is aq, there is no reaction period. Your source is wrong. The solubility of calcium phosphate is less than 1*10^-26.

If in fact it is listed as aq, then there is no reaction, and of course no net ionic equation.

If you get these errors often, I would consider changing instructors, as you will not get the point of chemistry. The point here is that in chemical reactions, certain ions are involved, and others are not. Evidence of a chemical reaction is formation of a precipated, a gas given off, ...
I will assume your instructor erred on the solubility of calcium phosphate.
Good luck

Answer 4

Bob Pursley is correct. Ca3(PO4)2 is insoluble and should be written as Ca3(PO4)2(s) unless it is in acid solution, and the net ionic equation he wrote also is correct. In addition to the two reasons he gave for a reaction to occur (gas formation and insoluble precipitate form), I would add a third for the purpose of writing net ionic equtions as "formation of a weak electrolyte".