1) State the equation that represents the chemical reaction
P2O5 + 3H2O → 2H3PO4
2) State the molar ratios: 1 mol P2O5 : 3 mol H2O : 2 mol H3PO4
3) Use the proportions 3molH2O / 2 mol H3PO4
0.729 mol H3PO4 * [ 3 mol H2O / 2 mol H3PO4] = 1.094 mol H2O
Answer: 1.094 mol of water
