A solution of 200 grams with a mass fraction of phosphoric acid of 9.8% Mixed with a solution of 200 g
A solution of 200 grams with a mass fraction of phosphoric acid of 9.8% Mixed with a solution of 200 g with a mass fraction of Na2HPO4 of 14.2% Determine the composition of the formed salt and its mass fraction in the solution
Determine the mass of the resulting salt using the following data:
Solution mass 1 – 200 g.
W – 9.8%.
Solution weight 2 – 200 g.
W 2 – 14.2%.
We write down the solution for this problem.
First, we write down the reaction equations.
Na2HPO4 + H3PO4 → 2 NaH2PO4.
Let us determine the mass and amount of the substance of the Na2HPO4 salt. We use the following formula.
m r.h. = W * m solution / 100%.
m = 200 * 0.098 = 19.6 g.
n = m / M.
M (Na2HPO4) = 23 * 2 + 1 + 31 + 16 * 4 = 142 g / mol.
n (Na2HPO4) = 19.6 / 142 = 0.14 mol.
m (H3PO4) = 200 * 0.142 = 28.4 g.
M (H3PO4) = 1 * 3 + 31 + 16 * 4 = 98 g / mol.
n = 28.4 / 98 = 0.29 mol.
Therefore, phosphoric acid is in excess.
0.14 mol Na2HPO4 – x mol NaH2PO4
1 mol – 2 mol.
X = 2 * 0.14: 1 = 0.28 mol.
m = 0.28 * 120 = 33.6 g.
W = 33.6 / (200 + 200) = 0.084 or 8.4%.
Answer: the mass fraction is equal to 8.4%.