# Determine the mass fraction of phosphoric acid in the solution obtained by dissolving 42.6 g

Determine the mass fraction of phosphoric acid in the solution obtained by dissolving 42.6 g of phosphorus (V) oxide in 200 g of water.

The synthesis reaction of phosphoric acid is described by the following chemical reaction equation:

P2O5 + 3H2O = 2H3PO4;

In this reaction, 1 mole of oxide reacts with 3 moles of water.

Let’s calculate the chemical amount of a substance that is in 42.6 grams of white phosphorus oxide.

M P2O5 = 31 x 2 + 5 x 16 = 142 grams / mol;

N P2 O5 = 42.6 / 142 = 0.3 mol;

Let’s calculate the chemical amount of a substance that is in 200 grams of water.

M H2O = 2 + 16 = 18 grams / mol;

N H2O = 200/18 = 11.11 mol;

0.3 mol of white phosphorus oxide will react with 0.3 x 3 = 0.9 mol of water.

In this case, 0.3 x 2 = 0.6 mol of acid is synthesized.

Let’s calculate its weight:

M Н3РО4 = 3 + 31 +16 x 4 = 98 grams / mol;

m Н3РО4 = 98 x 0.6 = 58.8 grams;

The weight of the solution will be:

M solution = m water + m oxide = 200 + 42.6 = 242.6 grams;

The mass fraction of acid will be equal to:

With acid = 58.8 / 242.6 = 0.242 = 24.2%;

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