Acid Base PH, POH

Question

Determine the pH of a 5.6 ×10^−4 M solution of Ca(OH)2

Answer 1

pH + pOH = 14

pOH = -log [OH^-]

Ca(OH)₂ is a strong base so it dissociates completely. There are 2 moles of OH^- ions per mole of Ca(OH)₂

[OH^-] = 2 x [5.6 x 10^-4] = 1.12 x 10^-3 (we will worry about sig figs later but note that original concentration had 2 sig figs)

pOH = -log [OH^-] = -log [1.12 x 10^-3]

= 3.0

pH = 14 - pOH = 14 - 3.0 = 11.0 = 11 (2 sig figs)