# what is the mechanism of water conductivity?

I'm trying to wrap my head around the kelvin water drop generator and more specifically what happens in the water before it drops. If on one side the drops of water are positive and on the other side negative, that means there is current flowing through the water before it drops.

What I dont understand even more specifically is how electricity is carried by water, and why water conductivity increases with ions content (and other impurities perhaps).

Are there electrons flowing ? Or are there ions flowing ? Let's imagine that we are below the potentials at whitch electrolysis occurs (about 1 volt). What carries the charges ?

I first thought that ions were responsible for the charges in the kelvin generator, but when a spark occurs, because the water has dropped into separate boxes it's impossible for them to move, so there must be some kind of redox reaction occuring. But if table salt is in the water to raise it's conductivity, would that mean that Na+ is reduced to sodium and Cl- oxydized to chlorine ?

• Water is an insulator. When you add salts, sat $\text{NaCl}$, you get ions and make water a conductor. – jinawee Jan 8 '14 at 20:09
• reading several other similar questions on stack exchange it seems this is considered a chemistry question, the most in depth answer on chemistry SE I found so far is : chemistry.stackexchange.com/questions/4979/… – Manu de Hanoi Jan 9 '14 at 6:31

## 1 Answer

Pure water is not a conductor of electricity. Normal water we get has impurities in the form of ions in it (minerals etc..). These ions are responsible for the electric conduction in water. Because the electrical current is transported by ions in water (and in any other solutions), the conductivity increases as the concentration of the ions increases.

Typical conductivity of water is: Ultra pure water (has H2O, and H+ and OH- ions in equilibrium) ~ 5.5 * 10-6 S/m Drinking water ~ 0.005 – 0.05 S/m

• so how do ions exchange electrons with a cathode or anode in the case of salt for example ? – Manu de Hanoi Jan 9 '14 at 4:20
• Positive ions are attracted towards the cathode (negative) and hence the name cations. Negative ions are attracted towards anode (positive) hence the name anions. Once the cations/anions reach the electrode (cathode/anode), it exchange electrons with the electrode thereby neutralising the ion. This exchanged electron with the electrode is responsible for the current through the external circuit. What happened to the neutral atoms (ions after neutralising at electrode)? They get deposited at the electrode. – albedo Jan 9 '14 at 6:30
• you cant deposit sodium in water – Manu de Hanoi Jan 9 '14 at 6:32
• I said what happen to the ions in the water. – albedo Jan 9 '14 at 6:38
• well we have table salt, as I mentionned in my question right ? It is made of Na+ and Cl-. Do you expect Na+ to be reduced in aqueous solution ? – Manu de Hanoi Jan 9 '14 at 6:40