To 200 g of a 10% solution of potassium hydroxide was added 25 g of pure potassium hydroxide.

To 200 g of a 10% solution of potassium hydroxide was added 25 g of pure potassium hydroxide. determine the mass fraction of the dissolved substance in the received solution.

1. Find the mass of potassium hydroxide in the original solution:

m1 (KOH) = w1 (KOH) * mout (solution) = 0.1 * 200 = 20 g;

2.Calculate the mass of hydroxide and solution after adding pure KOH:

mtot (KOH) = m1 (KOH) + madd (KOH) = 20 + 25 = 45 g;

m2 (solution) = mout (solution) + mdob (KOH) = 200 + 25 = 225 g;

3.determine the mass fraction of potassium hydroxide in the resulting solution:

w (KOH) = mtot (KOH): m2 (solution) = 45: 225 = 0.2 or 20%.

Answer: 20%.