Calculate the mass fraction of the solute in the solution if 10 g HBrO4 and 15 ml of water were taken for its preparation.

Given:
m (HBrO4) = 10 g
V (H2O) = 15 ml
ρ (H2O) = 1 g / ml

To find:
ω (HBrO4) -?

Decision:
1) Calculate the mass of H2O:
m (H2O) = ρ (H2O) * V (H2O) = 1 * 15 = 15 g;
2) Calculate the mass of the HBrO4 solution:
m solution (HBrO4) = m (HBrO4) + m (H2O) = 10 + 15 = 25 g;
3) Calculate the mass fraction of HBrO4 in the solution:
ω (HBrO4) = m (HBrO4) * 100% / m solution (HBrO4) = 10 * 100% / 25 = 40%.

Answer: The mass fraction of HBrO4 is 40%.