Question

If 21.6 grams of diphosphorus pentoxide and 8.2 grams of water combine to form phosphoric acid, how many grams of phosphoric acid must form

Answer 1

P2O5 + H2O = H3PO4

the balanced reaction

P2O5 + 3H2O = 2H3PO4

then

MW P2O5 = 283.89

MW of H3PO4 = 98

MW of H2O = 18

mol of P2O5 = mass/MW = 21.6/283.89 = 0.076085 mol of P2O5

mol of H2O = mass/MW = 8.2/18 = 0.45555 mol of H2O

then

ratio is

1 mol of P2O5 :3 mol of water

0.076085 mol of P2O5 will react with 3*0.076085 = 0.228255 mol of H2O; which we DO have, therefore P2O5 is limiting

then since rati ois 1:2 with respect of P2O5 and H3PO4

0.076085 *2 = 0.15217 mol of H3PO4 are expect to be produced

mass = mol*MW = 0.15217*98 = 14.91266 g of H3PO4