# What volume of a solution with a mass fraction of phosphoric acid of 40%

What volume of a solution with a mass fraction of phosphoric acid of 40% and a density of 1.25 g / cm3 can be obtained from phosphorus weighing 15 grams.

From the reaction equations, we find the number of moles:
4P + 5O₂ = 2P₂O₅.
P₂O₅ + 3H₂O = 2H₃PO₄.
n (P) = m / Mr = 15/31 = 0.484 mol.
x (P₂O₅) = 0.484 * 2/4 = 0.242 mol.
x (H₃PO₄) = 0.242 * 2/1 = 0.484 mol.
Knowing the number of moles, we find the mass of phosphoric acid:
m (H₃PO₄ thing) = n * Мr = 0.484 * 98 = 47.419 g.
Weight of 40% solution:
m (H₃PO₄ solution) = m / W solution * 100% = 47.419 / 40 * 100% = 118.548 g.
The volume of phosphoric acid is obtained through the density:
V (H₃PO₄ solution) = m / ρ = 118.548 / 1.25 = 94.839 cm³.

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