Distilled water alert

[Edwardv]

I am not going to argue about water anymore after this:

Distilled water is *pure enough*. Most companies even list the acceptable impurities on the outside of the bottle you buy it in. If CO2 is a problem, then just mix chemistry in a vacuum

Hear! Hear! Thank you....

 

[Edwardv]

I am not going to argue about water anymore after this:

Distilled water is *pure enough*. Most companies even list the acceptable impurities on the outside of the bottle you buy it in. If CO2 is a problem, then just mix chemistry in a vacuum

Hear! Hear! Thank you...

 

[Kirk Keyes]

Old values that I have placed it at about 6.5 in distilled water. However, I have to believe your values Kirk which only emphasizes the fact that the pH can vary with conditions, and pH is not a measure of purity by any means.

Ron - You should have kept reading the info on wikipedia below the table. It has the following paragraph:

For normal atmospherics conditions ( atm), we get a slightly acid solution (pH = 5.7) and the dissolved carbon is now essentially in the CO2 form. From this pressure on, [OH−] becomes also negligible so that the ionized part of the solution is now an equimolar mixture of H+ and HCO3−.

So, as you can see, given enough time, you will get a pH in the 5.Xs. THis matches with what I find experimentally.

Also, keep in mind that measureing pH with pH meters is made more difficult as the conductivity of the solution is so low the meter has a difficult time making a stable reading. It is not uncommon for the analyst to add a small portion of potassium chloride solution to boost the ionic strength of the solution to increase the conductivity of the solution to make the pH measurement more accurate. The KCl solution will not affect the overall pH, but it simply helps get a more stabile and accurate reading.

But your pH will/should be well below the 6.5 you mention given enough exposure to air.

 

[RobC]

My understanding is that water (H2O) is what is called an amphiprotic substance and that it reacts with itself. ie H2O + H2O gives H3O+(aq) and OH-

Therefore with no exposure to air or any other gas, it will ionize itself until it reaches its equilibrium at some point. And that means that pure H2O is unstable and even if you can get it to be pure 100% H2O it won't stay like that. And that hydrogen ionization is what determines the PH so the PH changes all by itself until it reaches equilibrium. But of course it really isn't pure to start with even after distillation or RO so what you end up with by way of any of these processes is something relatively free from contaminates but NEVER pure H2O unless it has been through very rigorous processes to purify it which would put the cost way above what us photographers would consider paying for it.

 

[Jordan]

Rob -- Auto-dissociation of water isn't considered an "impurity"-forming process. It is a basic property of water. There is no way to stop it.

 

[RobC]

Rob -- Auto-dissociation of water isn't considered an "impurity"-forming process. It is a basic property of water. There is no way to stop it.

Yes but it will change its PH from that obtained in pure H2O. And it will also change its electrical conductivity which also, I think, means it will change its reaction properties to other chemicals. I'm just making the point again, that pure 100% H2O is only to be found in the most stringently controlled lab conditions and its life is very short. Meaning, what people think distillation does for water is usually very wrong.

 

[Photo Engineer]

Kirk;

Yes, I read to the end. Yes, I believe your figures and understand the ionic strength.

My point is that pH is not reliable for a measure of DW purity, just an indication of purity. Other methods should be used to test. But, also, some DW is not DW but merely "purified" by some means such as RO.

Rob has explained it well in post #36 in plain English and you have given the technical detials. Also, I do remember getting values of about 6.0 - 6.5 for DW many years ago.

PE

 

[RobC]

Kirk;

Yes, I read to the end. Yes, I believe your figures and understand the ionic strength.

My point is that pH is not reliable for a measure of DW purity, just an indication of purity. Other methods should be used to test. But, also, some DW is not DW but merely "purified" by some means such as RO.

Rob has explained it well in post #36 in plain English and you have given the technical detials. Also, I do remember getting values of about 6.0 - 6.5 for DW many years ago.

PE

I think that without knowing 100% that water does not contain anything else, even in very small quantities, then PH does not indicate purity since PH is measured using electrical conductivity and that can be influenced by other things in the water. PH is simply a measure of Hydrogen ionisation but when you start looking at how difficult it is to measure PH accurately then you will see that even that will usually be unreliable except in labs with the most stringent testing procedures.

 

[jim appleyard]

My understanding is that water (H2O) is what is called an amphiprotic substance and that it reacts with itself. ie H2O + H2O gives H3O+(aq) and OH-

A bit OT, but is H3O what was known as "heavy water"?

 

[RobC]

A bit OT, but is H3O what was known as "heavy water"?

No

 

[k8do]

Well, I just grabbed the bottle of dip sticks for urine testing - pH/protein/glucose - and wandered down to the darkroom...
I use RO water from home which comes from my 200' deep well in 'chunks' (harder than the hubs of hell loaded with calcium and iron salts), goes through a salt water softener, then through the RO unit...
The pH of this water is ~5.0.. It has been in plastic gallon milk jugs for a week or more...

Then I tested the water from a 5 gallon jug of commercially supplied drinking water (which we drink from here at the office)... This is also a plastic jug, but certainly less permeable than the milk jugs... The water has been in the jug for weeks, at least...
The pH of this water is ~5.5... I assume this is RO water also...
On the bright side, there were no traces of protein or glucose in either water samples...

This RO water works just fine in my darkroom chemistry, and while an RO-distilled-deionized sequenced water source might be better I see no reason for any sudden changes... I am aware that the chemistry lab at the university uses commercial drinking water in 5 gallon jugs from the same vendor I use here at the office, for their life sciences labs, so I am in good company...
As far as the boiling water routine, I don't bother... The dissolved gases I drive off will magically reappear as I decant the water from one jug to another and stir the heck out of it mixing the chemicals <shrug> ....

Nearly 50 years ago my chemistry instructor called water the universal solvent... The passage of time has not proven any of his many aphorisms to be incorrect... He was a wise man...

denny

 

[Photo Engineer]

A bit OT, but is H3O what was known as "heavy water"?

D2O (deuterium instead of hydrogen) or T2O (tritium instead of hydrogen) both fall into the category of heavy waters. T2O and D2O can be used in nuclear weapons and both can be used for a variety of purposes related to nuclear technology.

The latest method of nuclear weaponry uses Lithium Deuteride made from D2O.

Drinking D2O will eventually kill any living thing when it reaches a certain percentage in cells, as the angle between the D and O changes as does hydrogen bonding. Basically, in non-technical terms, cells rupture due to the size change imposed by the heavy water. In simpler terms, it is larger and more spread out than normal water.

PE

 

[Kirk Keyes]

D2O (deuterium instead of hydrogen) or T2O (tritium instead of hydrogen) both fall into the category of heavy waters.

Perhaps some of the poster's confusion about this comes from the way these two compounds are normally written. Since D and T are not normally found on the Periodic Table, they are usually written as H(superscript 2) for Deuterium and H(superscript 3) for Tritium.

So when one sees "H30" written in ASCII text, they may be confused as to whether it is a Tritium Oxide of some sort, or 3 Hydrogens and one Oxygen - which should also have a plus 1 charge, which is also hard to write in ASCII text.

 

[Kirk Keyes]

My point is that pH is not reliable for a measure of DW purity, just an indication of purity. Other methods should be used to test.

I agree - but your original post seems to imply that there is an issue with the pH being not 6.5 or 7 in your 4 samples of water making it sound like there is a problem that you detected by checking the pH...

I've always wondered what the point of measuring pH of deionized waters was in the laboratory. I think it is a waste of time and does not convey much info about either the water or the pH meter quality or accuracy. Conductivity is a much better general indicator for inorganic contaminants, and if you have specific needs like a particular element/species or organics, then you need to do some much heavier duty testing than either pH or conductivity.

 

[Photo Engineer]

Kirk;

When I learned general chemistry, we used D and T for the two isotopes of Hydrogen. I continued that just by habit and actually use it so seldom that I have not seen the notation you descrube used often.

As for the original post, it was made to illustrate that the water we consider distilled actually contains a lot of potential for being impure. My initial wording was poor, I admit, but that has been brought out in the 60 or so posts made by others. It also shows that distilled water contains a fair amount of Carbon Dioxide which must be taken into account when designing processing solutions (where I first encountered it), and in making emulsions (another place where I encountered it). It must also be taken into account when mixing process chemistry and when DW is used as a final rinse.

It has also pointed out the great variation in what is called DW around the world. Most importantly, posts have shown us that volatiles of any sort can be carried across in the distillation process as much as non-ionic contaminants can be carried through some deionization processes.

Thus, DW may contain ammonia, many common organic solvents and some drugs which either distill directly or steam distill. Deionization would contain many organic solvents and drugs which are nonionic. Admittedly, they may be in trace amounts but they may have bad effects under certain circumstances. I cannot say. I merely did this as an alert, not a condemnation!

PE

 

[jim appleyard]

Thank you, gents, but you lost me a long way back. Anyway, using tap, distilled or "heavy water", I'm still having an explosive time with film.

 

[fhovie]

My local water in the tap tests at 6.5 - Of course my faith in ph testers is very low anyway. I look at my photos - the consistency of developing and printing and come to the conclusion that in the processes I use with the chemicals I use, tap water works fine. I also note that I have been drinking the tap water for 50 years with no ill effects. So - other than filtering I might do - I am not at all concerned with using tap water for photography with no modifications whatsoever. Of course I do notice that if it sits around too long, life will spontaneously evolve in it and so I need to dump it once in a while so I do not have to share my darkroom with other creatures. - Or at least I am told that is what smart people believe.

 

[Jordan]

Yes but it will change its PH from that obtained in pure H2O. And it will also change its electrical conductivity which also, I think, means it will change its reaction properties to other chemicals. I'm just making the point again, that pure 100% H2O is only to be found in the most stringently controlled lab conditions and its life is very short. Meaning, what people think distillation does for water is usually very wrong.

Rob, maybe I'm not being clear -- the "pure H2O" you're referring to (H2O that has not partially ionized to H+ and OH-) cannot be isolated, except perhaps as a very low-pressure gas in a cryogenic system. Liquid water is always auto-ionized with an equilibrium constant around 10E-14. If you go through the math, you'll see this corresponds to a degree of ionization of about 0.1 parts per million. This is just a fundamental property of water.

Anyway, this whole discussion is pretty much academic, as everyone probably realizes by now... the needs of 99% of home darkroom workers are met by distilled water from the grocery store, and if there is some concern about its quality, the thing to test is conductivity, not pH.

 

[Photo Engineer]

Jordan;

I agree. In fact, should never have started this thread.

BTW, there is some good reading on the internet with a search of "Distilled Water and pH". I'm surprised at how low the pH of DW can go and it is lower than I remember from General Chemistry. I guess it is old age.

PE

 

[Kirk Keyes]

It also shows that distilled water contains a fair amount of Carbon Dioxide which must be taken into account when designing processing solutions (where I first encountered it), and in making emulsions (another place where I encountered it). It must also be taken into account when mixing process chemistry and when DW is used as a final rinse.

Based on my titrations of DI water, the alkalinity of DI that has been exposed to air will be 1 mg/L bicarbonate or less.

It has no real buffering power and I hardly consider it to be concern at all, especially when used in photographic applications. It does not need to be considered at all...

 

[Photo Engineer]

Kirk;

Considering that some people equate that to 1 teaspoon of bicarb (see the google references above for adjusting pH of DW - I kid you not - they suggest bicarb or ammonia to adjust DW to the "proper" pH), I think you see my concern.

It is of special concern when you consider that minute adjustments of pH govern the speed and curve shape of some emulsions. This is where I first uncovered it. As it turns out, for my application the buffer capacity of gelatin overwhelmed the effect I expected to see due to the level of gelatin. It does become more important when I make a low gelatin emulsion though. That is what started this whole thing in my mind AAMOF.

PE

 

[Kirk Keyes]

We should probably go to the emulsion forum for this, but have you tried using a citrate/citric acid buffer in the emulsions? I was going to do that for my next trial. I was thinking pH to 6.0 or 6.5 with aforementioned buffer, and about 10 mM strength or so. Any thoughts?

 

[Kirk Keyes]

Considering that some people equate that to 1 teaspoon of bicarb (see the google references above for adjusting pH of DW - I kid you not - they suggest bicarb or ammonia to adjust DW to the "proper" pH), I think you see my concern.

Yes, these suggestions are rediculous.

 

[Photo Engineer]

We should probably go to the emulsion forum for this, but have you tried using a citrate/citric acid buffer in the emulsions? I was going to do that for my next trial. I was thinking pH to 6.0 or 6.5 with aforementioned buffer, and about 10 mM strength or so. Any thoughts?

Kirk;

This is a common method for adjusting the curve shape of some emulsions. See the book "Silver Gelatin" for reference.

PE

 

[RobC]

I guess it is old age.
PE

It's called a "Senior moment"