10 ml of 20% KOH solution (1.18 g / ml) was diluted to 500 ml. Determine the pH of the resulting solution.

Let’s calculate the mass of the initial KOH solution:

m (KOH solution) = 10 * 1.18 = 11.8 g.

Then, the mass of KOH in solution is found by the formula m (KOH) = (w (KOH) * m (KOH solution)) / 100.

m (KOH) = (20 * 11.8) / 100 = 2.36 g.

Chemical amount of KOH:

n (KOH) = 2.36 / 56 = 0.042 mol.

The molar concentration of KOH in the solution after dilution is calculated by the formula c (KOH) = n (KOH) / V (solution after dilution):

s (KOH) = 0.042 / 0.5 = 0.084 mol / L.

c (OH-) = c (KOH) * Degree of dissociation = 0.084 * 1 = 0.084 mol / L.

Let us write the equation for the dissociation of alkali:

KOH = K + + OH-

pOH = – log c (OH-)

pOH = – log 0.084 = 1.07.

pOH + pH = 14

Therefore pH = 14 – 1.07 = 12.93.