28.4 g of phosphorus oxide was dissolved in 200 g of water with heating. Find the mass fraction

28.4 g of phosphorus oxide was dissolved in 200 g of water with heating. Find the mass fraction of phosphoric acid in the resulting solution.

1. Let’s compose the reaction of phosphorus oxide with water:

P2O5 + 3H2O = 2H3PO4;

2.Calculate the chemical amount of the oxide:

n (P2O5) = m (P2O5): M (P2O5);

M (P2O5) = 31 * 2 + 5 * 16 = 142 g / mol;

n (P2O5) = 28.4: 142 = 0.2 mol;

3. Determine the amount and mass of phosphoric acid:

n (H3PO4) = n (P2O5) * 2 = 0.2 * 2 = 0.4 mol;

m (H3PO4) = n (H3PO4) * M (H3PO4);

M (H3PO4) = 3 + 31 + 4 * 16 = 98 g / mol;

m (H3PO4) = 0.4 * 98 = 39.2 g;

4. find the mass of the solution and the mass fraction of the acid:

m (solution) = m (P2O5) + m (H2O) = 28.4 + 200 = 228.4 g;

w (H3PO4) = m (H3PO4): m (solution) = 39.2: 228.4 = 0.1716 or 17.16%.

Answer: 17.16%.