Answer to Question #151410 in Inorganic Chemistry for robert

Question

What is the pH of a solution containing 5.6 mg / L of KOH, assuming it is completely dissociated?

Answer 1

concentration of KOH = 5.6mg/L = 5.6mg/dm³

5.6mg if KOH = 5.6×10-³/56 mol = 1 × 10-⁴ moles

Therefore,the concentration of KOH = 1×10-⁴moles/dm³ = 10^-4M

Now as pH is molar concentration of hydrogen ions of a specie, so we need to know molar concentration of hydroxide ion

$KOH \to K^+ + OH^-$

Therefore the concentration of the hydroxide ions is 10-⁴M.

Using the formula pOH = -log[OH^-] = -log(10^-4) = 4

but pH + pOH = 14

pH = 14 - 4 = 10

Therefore the pH of the potassium hydroxyl is 10