To 70 g of a 98% phosphoric acid solution was added 100 ml of water.

To 70 g of a 98% phosphoric acid solution was added 100 ml of water. Determine the mass fraction of acid in the new solution.

1) Calculate the mass of the solute of phosphoric acid in its solution. To do this, we multiply the mass fraction of the substance by the mass of the solution and divide by one hundred percent: 98 * 70/100 = 68.6 g.
2) Calculate the mass of added water. To do this, multiply the volume of water by its density: 100 * 1 = 100g.
Because water is added, then only the mass of the solution changes. The mass of the solute remains unchanged.
3) The mass of the solution after adding water: 70 + 100 = 170g.
4) Mass fraction of orthophosphoric acid in the resulting solution: 68.6 / 170 * 100 = 40.3% – answer.