Posted by **Tracy** on Tuesday, June 20, 2006 at 3:23pm.

Ok so a quick question. I have the equation Ca3(PO4)2 --> 3Ca+2 + 2PO4-3

Sorr its confusing, int he first part the 3 4 and too are all little numbers at the bottom, for the second part the +2 and -3 are small numbers at the top to show the charges. Ok so anyways the question says if the concentration of Ca2+ is 3.39 x 10^-7 mol/L in a saturated solution of Ca3(PO4)2 what is the concentration of PO4-3. The thing im confused about it, I dont know if that means you need to multiply the Ca concentration by three, then multiply by 2/3 to get the PO4 concentration or if the Ca concentration includes the 3 outside and then divde by 3 ND MULTIPLY by 2.

Ca3(PO4)2 ==> 3Ca^+2 + 2PO4^-3

For every x amount (in molar) of Ca3PO4 that dissolves, we will have 3X for (Ca^+2) and 2X for (PO4^-3). So you divide THE (Ca^+2) GIVEN (they didn't give you 3 times calcium, they gave calcium) by 2 to get X (which is Ca3(PO4)2 and multiply by 2 to obtain (PO4^-3). OK?

So you divide THE (Ca^+2) GIVEN (they didn't give you 3 times calcium, they gave calcium) by 2

Why 2 not 3? I'm so confused now. I divided by 3 then mulipied by 2

So sorry. I goofed. Divide Ca by 3 to get X, then multiply by 2 to obtain PO4.

Thanks very mcuh = )

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