pH of DM water is a mystery

A. Hi,

On reading your submission I started looking for this new boy on the block who calls himself Harry! I found that it was me back in January 2014.

Please supply some additional information without which too much unnecessary guesswork is required.
1) what was the name of the indicator?
2) what pH range does it cover?
3) You say that there was no change when you bubbled carbon dioxide though the water. What was the unchanging pH value that you got?

Harry

A. As the anion resin in the Mixed bed becomes exhausted, the pH will drop and silica will leak out of the resin.

A. Hi Manu,
I had a similar problem a few years ago. What was happening in my case was that the water was being pumped to a header tank and was dissolving atmospheric carbon dioxide, making a very weak acidic solution. Gentle heating to remove the carbon dioxide worked for me, moving the pH from around 5.5 to around 6.5.

This may not be practical for you; if not try to reduce the amount of churning of the water as it goes to the holding tank.

A. Hi manu,
In this case you firstly check whether there is any open space in the pipe line to allow the passage of carbon dioxide. If not then use morpholine which is an organic material used to maintain the pH only. And it will increase the conductivity but don't be scared about that; it will be in your desired value. Good luck.

A. Dear Manu Parameswaran,
After complete regeneration of MB when doing air mixing sudden settlement is necessary. If 2 types of resin don't mix well then heavy weight cation resin placed on bed. So, after air mixing sudden settlement is very important. You can try this I think your problem will be solved.

Thanking you,
With best regards,

A. It takes a special technique to accurately measure the pH of ultra pure water.

I believe one must add some KCl so that the water has some conductivity. Various companies sell kits with the needed solutions.

This might be of help:

https://www.coleparmer.com/tech-article/measuring-the-ph-of-pure-water

Got lots of good service from Cole-Parmer.

A. As Dave mentioned above, you've got to take extra care in measuring the pH of extremely low ionic strength solutions.
One phenomenon that you may be seeing the effects of is that of carbonic acid going into your water from exposure to CO2 in the air, and giving you a pH reading closer to 6 than to 7.

A. Hi Dheeraj,
As Brian Terry mentioned in 2015, you can heat the water gently to remove CO2 and get the pH up 6,0 to 6,5. Without adding anything, that's the only thing you can do.
Best of luck!

A. A nitrogen blanket & purge to remove dissolved CO2 may help. It is very difficult to measure the pH of high purity water with any accuracy because there is no buffering. Specialized cells are needed. In most cases the resistivity is sufficient to establish that the pH is very near neutral (6.5-7.5 at 20 °C).

A. Hi cousin Uday. Several people on this long thread gave the most probable cause, i.e., that measuring the pH of deionized water is difficult and requires specialized equipment. If you are using specialized equipment, please describe what equipment you are using.

With a generic pH meter, please recognize that conventional pH measuring equipment relies on the availability of large numbers of ions to conduct the chemical "synopsis", and when you remove those ions in de-ionizing columns but still try to read those currents accurately it's like trying to read millivolts on a 0-1000 volt meter or trying to judge how fast a snail is moving by pacing it with your car and watching the speedometer. Please study the page carefully. Good luck!

Regards,

A. Dear Uday,
If you rinse with DG water for about 1 to 1-1/2 hours, you can get 8.2 pH in anion bed outlet.

A. In a cation bed having Strong cation resin it adsorbed the hardness ions like calcium, magnesium (positive ions). Only these two ions determine the water hardness. Once raw water comes out from cation bed outlet, due to hydrogen ions the water is acidic -- the pH is low like 3 to 4.