As the title says, how is $\ce{Cu(OH)2}$ a base if it can't dissolve in water?

I mean if it can't dissolve in water then it won't produce any $\ce{OH-}$ ions.

And if it won't produce any $\ce{OH-}$ ions then how can it be called a base?

Same question for $\ce{Fe(OH)2}$ and every other base which is not an alkali.

I feel like this question is quite obvious and don't know how to describe it more. So please help.

  • 2
    $\begingroup$ You are using the Arrhenius definition of acids and bases, which only applies to substances that dissolve in water. The Bronsted-Lowry and Lewis definitions don't require water, so insoluble hydroxides can still be bases under these definitions. $\endgroup$
    – f''
    Aug 3 '16 at 5:19
  • $\begingroup$ oh, thx. Another question. My teacher gave us a question- "What happens when HCl gas is exposed to dry litmus paper". The answer was -"no reaction". Why is that so? $\endgroup$ Aug 3 '16 at 5:23
  • $\begingroup$ confusion-about-ph-of-a-substance - I had mentioned why things are acidic and why they aren't. $\endgroup$
    – Yashas
    Aug 3 '16 at 7:04
  • $\begingroup$ Dry HCl cannot dissociate and hence it won't be acidic. You need a medium such as water for HCl to dissociate. Acidic property shows up when there are free $H^{+}$ ions. $\endgroup$
    – Yashas
    Aug 3 '16 at 7:08
  • $\begingroup$ can it dissocciate when the weather is humid? $\endgroup$ Aug 3 '16 at 7:23

Copper (II) hydroxide has some small solubility in water, determined by its solubility product constant. More importantly, it will dissolve freely and act as a base if a suitable acid, such as acetic acid, is is available to be neutralized. See also the comment from @f".


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