Is Pure Water Really Non-Conductive?

[KingNothing]

I understand water in its purest form is non-conductive, or something like that.

I also know that there will always be some ions no matter how clean the water is...what kind of ions are these?

Are they enough to actually make it, say, carry some voltage a few inches and light a light bulb or something like this?

 

[Gokul43201]

I understand water in its purest form is non-conductive, or something like that.

If,by non-conductive, you mean "a very poor conductor", then yes, this is true.

I also know that there will always be some ions no matter how clean the water is...what kind of ions are these?

$H^+~and~OH^-$ ions.
There will be about $10^{-7}$ moles (or about $3.3*10^{18}$ ions) of each kind, per liter of water. This is actually a very small number.

Are they enough to actually make it, say, carry some voltage a few inches and light a light bulb or something like this?

I would have to say no. The resistivity of pure water is about 18 megaohm-cm. This is a really large number. You can make the resistance a manageable number but it would take a crazy geometry (extremely small L/A) and large electrodes, and of course, an AC source. At a length of "a few inches" you will need an area of several squre miles, I presume (but haven't really calculated).

 

[cosmik debris]

I understand water in its purest form is non-conductive, or something like that.

I also know that there will always be some ions no matter how clean the water is...what kind of ions are these?

Are they enough to actually make it, say, carry some voltage a few inches and light a light bulb or something like this?

Yes, pure water is a very poor conductor. Every year the students here have to build a radio receiver, one year one group built their radio circuitry immersed in de-ionised water. It looked spectacular.

 

[KingNothing]

So there won't be any H3O ions?

 

[AntonVrba]

Yes, pure water is a very poor conductor. Every year the students here have to build a radio receiver, one year one group built their radio circuitry immersed in de-ionised water. It looked spectacular.

And for how long did it work as pure water is also very aggressive and will disolve some of the metal i.e of the copper conductors, lead/tin etc and the resistivity would immediately drop.

For this reason you will not find de-ionized water being piped in metal pipes

 

[DaveC426913]

Why does the hydrogen not escape? If a certain % of weater is ionized as H and OH, won't some of the H be lost? I realize that, bering ionized, it will tend to stay with the OH molecules, but I would have thought that some would effectively "evaporate" over time, and an overwise undisturbed volume of water open to the air would eventually become (acidic? alkaline? I always forget which is which).

 

[Gokul43201]

And for how long did it work as pure water is also very aggressive and will disolve some of the metal i.e of the copper conductors, lead/tin etc and the resistivity would immediately drop.

For this reason you will not find de-ionized water being piped in metal pipes

I can't imagine they kept under DI for very long. You're absolutely right...copper will start corroding pretty fast in DI.

 

[Gokul43201]

Why does the hydrogen not escape? If a certain % of weater is ionized as H and OH, won't some of the H be lost? I realize that, bering ionized, it will tend to stay with the OH molecules, but I would have thought that some would effectively "evaporate" over time, and an overwise undisturbed volume of water open to the air would eventually become (acidic? alkaline? I always forget which is which).

Actually, the H+ ions attach themselves to H20 molecules (through a version of the hydrogen bond), forming H3O+ ions (as KingNothing mentioned above).

 

[cosmik debris]

I can't imagine they kept under DI for very long. You're absolutely right...copper will start corroding pretty fast in DI.

That's right, they only have to demonstrate the thing in front of a class for a few minutes or so.