Determine the composition of the formed orthophosphoric acid salt and its mass fraction in the solution

| April 28, 2021 | education

Determine the composition of the formed orthophosphoric acid salt and its mass fraction in the solution, if in a solution of sodium hydroxide (density 1.28 g / ml) with a volume of 25 ml with a mass fraction of NaOH of 25%, all phosphorus oxide 5 obtained by oxidation of phosphorus with a mass of 6.2 g was dissolved.

Let’s find the amount of phosphorus substance P according to the formula:

n = m: M.

M (P) = 31 g / mol.

n = 6.2 g: 31 g / mol = 0.2 mol.

Let’s compose the reaction equation, find the quantitative ratios of substances.

4 P + 5 O2 = 2 P2O5.

According to the reaction equation, there is 2 mol of P2O5 per 4 mol of P. Substances are in quantitative ratios 4: 2 = 2: 1.

n (P2O5) = ½ n (P) = 0.2: 2 = 0.1 mol.

Find the mass of the NaOH solution.

m = Vp.

m = 25 ml × 1.28 g / ml = 32 g.

W = m (substance): m (solution) × 100%,

m (solution) = (m (substance): W) × 100%,

m (solution) = (8 g: 25%) × 100% = 8 g.

Let’s find the amount of NaOH substance by the formula:

M (NaOH) = 40 g / mol.

n = 8 g: 40 g / mol = 0.2 mol (excess).

6 NaOH + P2O5 = 2Na3PO4 + 3H2O

n (Na3PO4) = 2n (P2O5) = 0.1 × 2 = 0.2 mol.

Let’s find the mass of Na3PO4.

m = n × M,

M (Na3PO4) = 164 g / mol.

m (Na3PO4) = 164 g / mol × 0.2 mol = 32.8 g.

m (solution) = m (NaOH solution) + m (Na3PO4) = 32 g + 32.8 = 64.8 g.

W = (32.8g: 64.8g) × 100% = 50.62%.



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