Question

Lars is balancing equations with his study group. He is unsure about one equation because each member of the study group came up with a different answer. Which is the proper way to balance the equation Ca(OH)2 + H3PO4 → Ca3(PO4)2 + H2O?

Ca(OH)2 + H3PO4 → Ca3(PO4)2 + 6H2O
3Ca(OH)2 + 2H3PO4 → Ca3(PO4)2 + 6H2O
3Ca(OH)2 + 2H3PO4 → Ca3(PO4)2 + 3H2O
Ca(OH)2 + 2H3PO4 → Ca3(PO4)2 + 6H2O

Answer 1

3Ca(OH)2 + 2H3PO4 → Ca3(PO4)2 + 6H2O

Check:
- Ca: 3 left, 3 right
- P: 2 left, 2 right
- H: (3×2) + (2×3) = 6 + 6 = 12 left; 6×2 = 12 right
- O: (3×2) + (2×4) = 6 + 8 = 14 left; (1×8) + 6 = 14 right

So the balanced equation is 3Ca(OH)2 + 2H3PO4 → Ca3(PO4)2 + 6H2O.