Determine the mass of a 4% potassium nitrate solution prepared (by diluting with water) from 20 g

Determine the mass of a 4% potassium nitrate solution prepared (by diluting with water) from 20 g of a 15% solution of the same substance.

1) Find the mass of potassium nitrate in a 15% solution:

m (KNO3) = m (p-pa 1) * ω1 (KNO3) = 20 * 0.15 = 3 g.

2) When diluted with water, the mass of potassium nitrate has not changed, but now these 3 grams are 4% of the mass of the solution. Means:

m (p-pa 2) = m (KNO3) / ω2 (KNO3) = 3 / 0.04 = 75 g.

Answer: 75 g.