Electricity and impure water

1. Jun 18, 2006

scott_alexsk

Does electricity only conduct in impure water or can it also conduct in distilled water? If one was to drop an electrical appliance in the ocean how far if at all would noticable current spread?

Thanks,
-scott

2. Jun 18, 2006

if you have VERY pure water then it would be a poor conductor and you could say that it would not conduct electricity. However even small amounts of salts (or other impurities) will increase electrical conductance.

As for the electrical appliance in the ocean, i'm not too sure. Maybe somebody else can answer this.

3. Jun 18, 2006

mrjeffy321

PURE water, in the purest sense, does not conduct electricity.
Water needs to have some type of electrolyte in order to allow an electrical current to be conducted through.
Distilled water should not conduct any significant amount of electrical current.

Electricity (movement of charged particles) flows between two sources of electrical potential.
If you dropped a toaster into the ocean, the electrical potential across the toaster is looking for the path of least resistance to the ground. The easiest way would be to head straight over to the opposite electrode in the toaster, short circuiting it. But there are also other path's the electricity can take to get to ground...it could take the long way and go through the entire ocean until it reaches the bottom or land, but this is a far more complicated path for the electricity to take and only a fraction of the total current would take this path. Most of the current should stay within the toaster, between the two electrodes I would think.

4. Jun 18, 2006

Gokul43201

Staff Emeritus
No, and yes.

Why should there be any current at all?

PS : Jeffy, even pure H2O has a finite resistivity (about 18 megaohm-cm), hence non-zero conductivity.

5. Jun 18, 2006

mrjeffy321

I have heard to argument made that even pure water conducts to a degree since in reality, "pure" water does not exist.
liquid water exists in a state of equilibrium between H+ and OH- ions in solution withitself,
H2O (l) <---> H+ (aq) + OH- (aq)

Also, CO2 from the air will dissolve in the water to form Carbonic acid which will weakly dissassociate into H+ and CO3- ions, providing for the conduction of an electric current.

6. Jun 19, 2006

scott_alexsk

If impure water has that much resistance to conduction than why should someone be killed or seriously injured if that person accidently droped an electrical appliance in the bathtub.
-scott

7. Jun 19, 2006

mrjeffy321

Impure water does not have nearly as much resistance as pure water.

I have never known anyone to fill up a bath tub with distilled water...most people use tap water. Tap water has certain ions dissolved in it, some are put there intentionally by the city (F- for example), and others get there unintentionally (Ca + 2 for example). These ions allow for the conduction of an electric current.

The ion concentration of tap water is not very high, it still has a significant electrical resistance, but never the less, when applying high voltages to the water, such as those you might find in an electrical appliance, a current will conduct.
V = RI

Current killsâ€¦.and it does not take all that much current to kill you if it passes through the right part of your body.

8. Jun 19, 2006

Even if someone filled the bath tub with distilled water, there's still enough salt on the human body (i.e. from sweat) to add quite a few ions into the tub.

9. Jun 20, 2006

Gokul43201

Staff Emeritus
That's at the very best, a poor argument. I hope you didn't read it in a book. If "pure" water doesn't exist, how can someone make a statement about its properties?

In any case, even theoretically, pure water has a finite AC resistivity, primarily due to the presence of hydronium and hydroxyl ions (as you mentioned above).

10. Jun 21, 2006

mrjeffy321

No, I dont think I read it in a book......but I do specifically remember hearing my PhD possessing Chemistry professor state it as fact at least once.
Just another reason I hate my school's chemistry department.

Last edited: Jun 21, 2006
11. Jun 21, 2006

Integral

Staff Emeritus
I have never seen any reluctance for the scientific community to speak of theoretical properties of things that are either very difficult or impossible to obtain. "Pure" water could well be considered in this category. Anyone who has spent any time around a commercial DI water system is aware of how difficult it is to maintain a resistivity of even 14Mohm -cm DI. Distilled water is NOT DeIonized so will have a relatively high conductivity on the scale of DI systems. Many commercial wet benches routinely use DI by the hundreds of galleons, so a bathtub full is not all that remarkable, as long as the bathtub is made of PTFE or some similar plastic.

The reason a bathtub full of soapy water or even tap water is an excellent conductor is because it is NOT pure, in fact it is a LONG way from being pure. I believe MrJeffery's prof, pure water is in fact non existent.