Calculate the mole fraction of phosphoric acid in a 29.1% (by mass) aqueous solution.

Answer 1

To find mole fraction of phosphoric acid, we need t find moles of acid and moles of water and total moles.

29.1% (w/w) H3PO4 = 29.1 g H3PO4 / 100 g solution.

If we have 100 g solution, and 29.1 g is H3PO4, then the remainder is water

mass of water = 100 g - 29.1 g = 70.9 g H2O

moles H3PO4 = 29.1 g x 1 mol / 97.995 g = 0.2970 moles

moles H2O = 70.9 g x 1 mol / 18 g = 3.939 moles

Total moles = 4.236 moles

mole fraction H3PO4 = 0.2970 mols / 4.236 mols = 0.0701