Chemistry Stoichiometry

Question

PCl5 + 4 H2O → 5 HCl + H3PO4

a) How many moles of phosphorus pentachloride are needed to react with 235 g of water?

b) How many grams of H3PO4 will be produced in a reaction that forms 62.7 g of HCl?

Answer 1

PCl5 + 4 H2O → 5 HCl + H3PO4 ... balanced equation

a). From the balanced equation, 4 moles H2O react with 1 mole PCl5. Using this ratio, we calculate the moles of water and then moles of PCl5:

235 g H2O x 1 mol H2O / 18 g = 13.1 moles H2O

13.1 mols H2O x 1 mol PCl5 / 4 mols H2O = 3.28 moles PCl5

b). Again, we will use the mol ratio of HCl to H3PO4, but first must convert grams to moles:

62.7 g HCl x 1 mol HCl / 36.5 g = 1.72 mols HCl

1.72 mols HCl x 1 mol H3PO4 / 5 mols HCl = 0.344 mols H3PO4

0.344 mols H3PO4 x 98.0 g H3PO4 / mol = 33.7 g H3PO4