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Home > Curriculum Support > High School / Senior High > Chemistry 3rd Edition > How do I balance the equation in On Your Own 9.4c?
How do I balance the equation in On Your Own 9.4c?
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You start out with:

H3PO4 + Mg(OH)2 –> Mg3(PO4)2 + H2O


Stay away from the H’s and O’s at first, because they appear in multiple substances on at least one side of the equation. Thus, we start with P and Mg. To balance P, multiply H3PO4 by 2:

2H3PO4 + Mg(OH)2 –> Mg3(PO4)2 + H2O


To balance Mg, multiply Mg(OH)2 by 3:

2H3PO4 + 3Mg(OH)2 –> Mg3(PO4)2 + H2O


Now look at H’s, because they appear only once on the products side. There is 2×3 + 3×2 = 12 H’s, so multiply H2O by 6:

2H3PO4 + 3Mg(OH)2 –> Mg3(PO4)2 + 6H2O


Now the O’s are balanced, too (2×4 + 3×2 = 14 on reactants side, 4×2 +6×1 = 14 on products side).

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