# 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 Remember: The process of learning a person lasts a lifetime. The value of the same knowledge for different people may be different, it is determined by their individual characteristics and needs. Therefore, knowledge is always needed at any age and position.