# To 40 ml of a 20% solution of potassium nitrate with a density of 1.13 g / ml was added 30

**To 40 ml of a 20% solution of potassium nitrate with a density of 1.13 g / ml was added 30 ml of a 10% solution of the same salt. What is the mass fraction of potassium nitrate in the solution?**

Given:

V1 = 40 ml,

V2 = 30 ml,

w1 = 20%,

w2 = 10%,

p = 1.13g / ml.

w3-?

Solution:

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

m (solution) = V p.

m (solution) 1 = 40 ml × 1.13 g / ml = 45.2 g.

m (solution) 2 = 30 ml × 1.13 g / ml = 33.9 g.

m (solution) 3 = 33.9 g + 45.2 g = 79.1 g.

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

m (substance) 1 = (45.2 g × 20%): 100% = 9.04 g.

m (substance) 2 = (33.9 g × 10%): 100% = 3.39 g.

m (substance) 3 = 9.04 g + 3.39 g = 12.43 g.

Let’s find the mass fraction of the substance in the resulting solution.

W3 = (12.43: 79.1) × 100% = 15.71%.

Answer: 15.71%.