0.2 dm3 of a KOH solution with a concentration of 0.5 mol / dm3 was diluted with water to 1 dm3 and stirred.

0.2 dm3 of a KOH solution with a concentration of 0.5 mol / dm3 was diluted with water to 1 dm3 and stirred. What is the pH of the resulting solution?

Find how many moles of potassium hydroxide are in the solution. n = v * Cm = 0.2 L * 0.5 mol / L = 0.1 mol.
The solution was diluted from 0.2 L to 1 L; accordingly, the concentration dropped: Cm = 0.1 mol / 1 L = 0.1 mol / L.
Potassium hydroxide decomposed into ions according to the equation: KOH = K + + OH-.
The concentration of hydroxyl ions is equal to the concentration of the outgoing substance, since potassium hydroxide is a strong electrolyte. Let us find pOH, which is equal to the negative logarithm of the OH- concentration.
pOH = -lg [0.1] = 1
pH = 14 – pOH = 14 – 1 = 13