Imagine an unsaturated(No Ca(OH)2 (s) just Ca2+ (aq) and OH- (aq)) aqueous solution of Calcium Hydroxide.

Is the following equilibrium present in that solution and does the transparency of an unsaturated Calcium Hydroxide vanish after a while?

$$\ce{ Ca^2+_{(aq)} + 2OH- _{(aq)} <=> Ca(OH)2_{(s)}}$$

  • 2
    $\begingroup$ No and no (well, in real world the solution might get cloudy, but that's for entirely unrelated reasons). $\endgroup$ Mar 24, 2016 at 8:15

1 Answer 1


Equilibria in solutions are given as solubility products, $K_{\text{sp}}$. Your reaction is:

$$\ce{Ca(OH)_2 <=> Ca^2+ + 2OH-}$$ for this, $K_{\text{sp}}=5.5\times 10^{-6}$ (from Wikipedia). What this means, is that in a saturated solution, at equilibrium, you will have: $$K_{\text{sp}}=[\ce{Ca^2+}] [\ce{OH-}]^2=5.5\times10^{-6}$$

However, for an unsaturated solution, you will have:

$$[\ce{Ca^2+}] [\ce{OH-}]^2 <K_{\text{sp}}$$

As mentioned the solution does get cloudy for different reasons, namely the formation of $\ce{CaCO3}$ by reaction with $\ce{CO2}$.


Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.