Does RO/DI water even have a pH? (Any H+ / OH- ions?)

[Mickes]

When you test the pH of RO/DI water, you are usually testing the pH of the test kit itself... Also RO/DI water does lean toward the Acid side cause of CO2 that has been absorbed by the water.

 

[kazzoo]

Mickes and Jdeets are correct. RO/DI will have a pH slightly on the acidic side because of carbon dioxide dissolution in the water.

 

[Nathan1]

Carbon Dioxide? From where? The atmosphere?

We all know that pure water doesn't conduct electricity very well, so how do you measure the pH of pure water with an electronic pH probe?

-Nathan

 

[kazzoo]

Yes, from the air. It will diffuse into the water from the air at the air/water interface.

 

[Mickes]

Nathan: You can't test for pH on RO/DI water with one of the pH probes that we normally use in the hobby. I think, however, that the multi thousand $$ lab grade pH probes will do the trick.

 

[Nathan1]

I guess that's why I was getting *REALLY* crazy readings when I tried to test pH of my RO/DI water...

-Nathan

 

[Nathan1]

How is it possible to measure the pH of pure H2O if there are no other chemicals in it? Does it even have a pH?

We all know that pure water doesn't conduct electricity very well, so how do you measure the pH of pure water with an electronic pH probe?

-Nathan

[ July 20, 2001: Message edited by: Nathan ]

 

[Enkidu]

it should have a neutral pH, right? Shouldn't it be a pH of 7? Thats what I would expect.

 

[jdeets]

That's what I would *expect* as well. However, usually it will actually have a pH that is somewhat acidic. Mine tests at 5.5 straight out of the unit.

 

[Tanu]

Indeed, carbon dioxide is absorbed from the air. But, say, you store AND make the RO water in a room without gasses ('air'). Than, the pH would be 7. Why? H2O is water, but, in the water there ALWAYS is a balance between H+ and OH-, these ions come from the water itself! And, add H+ to OH-, and you'll get water!

Tanu www.tanu.nl