Why doesn't pure water conduct when it dissociates?

Question

Sorry if this is an obvious question.

I am told water dissociates, one product of which is negatively charged hydroxyl ions. This makes sense, but then why doesn't pure water conduct electricity? Surely the hydroxyl ions could act as charge carriers to allow current to pass through the solution?

Thanks

Presumably due to the low ionisation of water? Is there a certain amount of conductivity below which we say something doesn't conduct? @MaxW — Controller, Sep 26 '20 at 09:12
LOL - Well in capacitors the conductance is so low that it is called "leakage" not "conductance." — MaxW, Sep 26 '20 at 09:14
@ Controller. You are right. In pure water, the concentration of the ions is $\ce{10^{-7}}$ M. So the currant is about $\ce{10^{-7}}$ times the value obtained with a $1$ M solution of electrolyte. It is probably some nanoamperes. It looks as if water does not conduct. Or, following MaxW, the currant may be considered as leakage currant. — Maurice, Sep 26 '20 at 09:50
Currant? Sounds yummy, actually. Current, with an "e", is more closely related to electricity. — Oscar Lanzi, Sep 26 '20 at 12:41
Does this answer your question? Why can't pure water conduct electricity since it can be reduced at cathode and oxidised at anode? — Mithoron, Sep 26 '20 at 16:07

napstablook · Answer 1 · 2021-06-19T01:59:34.233

4

Pure water does conduct as pointed out by the above comments. But it has very less dissociation hence there are very few ions to conduct electricity.

you may have heard that $pH$ of pure water is 7. This statement implies that the concentration of H+ ion is $10^{-7}$. Since it is a neutral solution concentration of $\ce{OH^{-}}$ ion is also $10^{-7}$. As such the conducting property of water is very less.

edited Jun 19 '21 at 01:59

answered Sep 26 '20 at 15:09

napstablook

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Why doesn't pure water conduct when it dissociates?

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