How do I balance this equation?

Question

H_3PO_4 + Mg(OH)_2 > Mg_3PO_4 + H_2O

Answer 1

This equation doesn't balance.

H3PO4 + Mg(OH)2 → Mg3PO4 + H2O

Let's start with Mg. There is one Mg atom on the left and 3 on the right, all in one compound. So the coefficients on the left must be three times that on the right for the compounds containing Mg . Let's call them "3a" and "a". Now we have:

H3PO4 + 3aMg(OH)2 → aMg3PO4 + H2O

Next is P. There is one P atom on each side so the coefficients of those compounds must be the same. Since one is already "a" the other must be "a" also. Now we have:

aH3PO4 + 3aMg(OH)2 → aMg3PO4 + H2O

Now let's look at O. There are 4a + 2*3a = 10a atoms of O on the left. So we must have the same number on the right. On the right we have 4a + __ = 10a. So the last coefficient is 6a. Now we have:

aH3PO4 + 3aMg(OH)2 → aMg3PO4 + 6aH2O

Set a = 1 and we have:

H3PO4 + 3Mg(OH)2 → Mg3PO4 + 6H2O

As a check let's see if H balances. We didn't check that one.

We have

3 + 3*2 → 6*2
9 → 12

But this is false. So it doesn't balance. If you check the "solutions" of the other answers, they don't balance.

Answer 2

The answer should be
2H_3PO_4 + 3Mg(OH)_2 = Mg_3PO_4 + 6H_2O

Answer 3

2H3PO4 + 3Mg(OH)2 <=> Mg3PO4 + 6H20

Answer 4

that's doesn't make any sense. what's the equation? what's _?