Technical potassium hydroxide weighing 3.5 g was dissolved in water, receiving 500 ml of solution. According to chemical analysis

Technical potassium hydroxide weighing 3.5 g was dissolved in water, receiving 500 ml of solution. According to chemical analysis, the molar concentration of the solution was 0.1 mol / L. What is the mass fraction of KOH in the substance

Given:
Mr (KOH) = 56g / mol;
Cm (KOH) = n (KOH) = 0.1 mol / L;
V (r-ra) = 500ml or 0.5l;
mtechn. (KON) = 3.54g.
w% (KOH) =?
Decision:
First, calculate the amount of potassium hydroxide in the solution:
n (KOH) = Cm * V (solution) = 0.1 mol / L * 0.5 L = 0.05 mol.
Find the mass of pure potassium hydroxide:
m (KOH) = n (KOH) * M (KOH) = 0.05 mol * 56 g / mol = 2.8 g
Now we calculate the mass fraction of KOH in the technical sample of it, we get:
w% (KOH) = m (KOH) * 100% / mtechn. (KOH) = 2.8 g * 100% / 3.5 g = 80% or 0.8