How do strong acids conduct electricity in water?

I have just studied ionization of water and I'm confused about some points. First: I know that water ionizes in a very small amount ($10^{-14}$) so it doesn't conduct electricity and if we add strong acid (or base) to it , it becomes a good conductor of electricity. My question here is how it conduct electricity although if a strong acid is in water its $\ce{H+}$ ions concentration in water would range from $10^{-1}$ to $10^{-6}$ (which is avery small amount) to keep $K_w$ constant. I'm confused so if you understood me please explain and tell me if I have something wrong

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    $\begingroup$ Acids (and other electrolytes) in water solutions conduct electricity because ions. Ions come from dissociation. Water by itself doesn't dissociate very well. Acids (and other electrolytes) do. What's unclear about that? $\endgroup$ – Ivan Neretin Jan 22 at 19:16
  • $\begingroup$ @Eman, The "how" part of your query is pretty difficult and perhaps still not understood well. The fact that you should keep in mind is that the proton in water has the highest known conductivity, this is followed by hydroxide ion. So both H+ and OH- are strong conductor. Search the keyword Grotthuss mechanism. $\endgroup$ – M. Farooq Jan 22 at 21:37
  • $\begingroup$ Acidic solutions with $\ce{H+}$ concentrations around $10^{-5} - 10^{-6} M$ are not good conductors. They are better than water, but not that much. $\endgroup$ – Maurice Jan 23 at 10:38
  • $\begingroup$ @ivanneretin i am confused about how this small amount 10^-2 can conduct electricity in strong acid, while we say that sulphourous acid is a weak acid that doesnt conduct electricity because its equilibrium constant equals 1.7*10^-2 tell me if I'm wrong $\endgroup$ – Eman Jan 23 at 16:57
  • $\begingroup$ $10^{-2}$ is not a small amount. Then again, everything conducts electricity. Some things do it well, and some not so well, and some do it poorly, and some yet worse, and some are ten orders of magnitude worse than that, and there are levels upon levels upon levels even below that. What do you really mean when you say "doesn't conduct electricity"? $\endgroup$ – Ivan Neretin Jan 23 at 17:28

In water at 25 ºC $[H+]=[OH-]=10^{-7}M$, so a concentration of $[H+]=10^{-6}M$ is very low. With a strong acid like HCl you have to dissolve only around 35 micrograms in a liter of water to get this concentration.

Sea water on the other hand has a high conductivity and, in average, 35 grams per liter of salts dissolved in it. If you dissolve 35 grams of HCl en 1 liter of water you have $[H+]=1M$ and surely you can expect a high conductivity.

These are gross numbers, but I think they help to get the idea.

Conductivity of a solution depends on the free ions present on the mixture. With a strong acid you can get a high concentration of ions using a little quantity of acid. With a weak acid you need much more.


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