To 300 g of a 15% potassium hydroxide solution was added 200 g of a 7.5%

To 300 g of a 15% potassium hydroxide solution was added 200 g of a 7.5% solution of the same substance. What is the mass fraction of KOH in the solution?

Given:

m (first solution) = 300 g

m (second solution) = 200 g

w% (first solution) = 15%

w% (second solution) = 7.5%

Find:

w% (in final solution) -?

Solution:

1) Find the mass of the total solution after draining:

m (solution) = 300 g + 200 g = 500 g;

2) Find the mass of alkali in each solution:

m1 (KOH) = 300 g * 0.15 = 45 g

m2 (KOH) = 200 g * 0.075 = 15 g

3) Find the mass of alkali after draining:

m (KOH) = 45 g + 15 g = 60 g;

4) Find the mass fraction of potassium hydroxide in the final solution:

w% (KOH) = m (KOH): m (solution) * 100% = 60 g: 500 g * 100% = 12%.

Answer: w% (KOH) = 12%.