NH3 and H20

By searching on a few terms combining aqua, ammonia, and conductivity, the dozen or so hits I looked at did not show this property. Information was better on pH and specific gravity.

For an experimental approach, how about taking some measurements with suitable instruments for each property, and graphing the correlations?

Hello Guest,

Read this fairly short answer to your question as to what the problems with the solution to your query are:

http://www.newton.dep.anl.gov/askasci/chem99/chem99571.htm

Mike

There is no direct correlation between pH and conductivity.

This is because conductivity is a factor of all ions in a solution not just the hydronium ions.

Beat you!

The NH3 will increase the conductivity of the water. Pure water, such as tripple distilled, has about the highest conductivity that you can get. Almost anything at all soluble added to it will increase the waters conductivity some.

" Pure water, such as tripple distilled, has about the highest conductivity that you can get."

What? Please explain this statement to me. I must be missing something.

Mistake caused by 32 hr extremely stressfull day. Pure water such as tripple distilled H2O has the lowest conductivity (i.e. highest resistance, highest impedance) that you can get for materials or mixtures suitable for testing by this method. Addition of just about anything even the slightest soluble in H2O will increase the conductivity of the water (lower its resistance to the flow of electricity)

My apologies to anyone who I may have misled. I am a volunteer fire chief and it was a real big fire which took a long time to put out. Fortunately no one was hurt.

No apologies needed. I figured that I must have been at the races on the day we covered that in class. There was a horse race track 30 miles from my school.

I'm glad to hear there were no injuries.

der all, I know that there is no direct relationship between the pH and the conductivity (I learned this from Google and some basic Chemetry books). That is why I specified the conductivity to be less than 0.1µS/cm. Assumming that nothing else but the NH3 is adding to the conductivity is it possible to calculate the resulting end conductivity? Do I need to specify more details?

Thanks

Guest

In general there may be no correlation between pH and conductivity, but in the specific case of water-ammonia mixtures (with nothing else to influence one of these more than another), there might be a decent correlation. I don't know if there is such a correlation, but it might be worth checking.

What is your real goal? Constant pH? Then why not just measure that and adjust the mix accordingly? Of course, if conductivity is easier/cheaper/less sensitive to measure, and if a correlation to pH can be established (for this specific case), then conductivity will be a good surrogate for pH.

There are some ifs here, but the original question is good.

[I have a similar quest to measure near-eutectic salt brine concentrations in real time. Hydrometers and even refractometers are slower than I would like. It would be nice if I could measure conductivity (or something else) on the fly, but that much salt in the water is out of the range of any instruments I have found so far.]

Tornado, the reason behind the question is that I have seen a specification where it says that the pH shall be 9-10 and the conductivity ≤6.2µS/cm. This is to do with the generation of steam and the pH is adjusted with NH3 to protect the pipework. I was just wondering if the pH was 10 would the conductivity still meet the requirement of being ≤6.2µS/cm (assumming that the only contributor to the conductivity was the NH3). I believe that the NH3 dosing is controlled from the conductivity, so I guess that there must be some sort of link.

Hope this shines a bit more light on why I was asking the question.

Thank you for taking the time to engage with me on this subject.

My apologies, you did stipulate that the NH3 will be the sole source for an ion pair. Now from here you will find a simple equation that quickly gets very complicated when more than a few ion pairs get dissociated. (Hmm, Google Chrome has no access to the Greek characters. I'll have to come back and see if and how the link posted. In case nothing gets linked here's the raw url http://www.wileywater.com/Contributor/Sample_2.htm ) Don't forget that despite the nice linear relationship of the original equation, all of the variables cited (density of water, equivalent ionic conductance of ion and concentration of ion) have non-linear characteristics. What should perk your interest is Figure 4 of the linked page. It is a multiple trace graph of different sole ionizers in pure water at different concentrations. While NH4OH is not listed, it will give you a reference to work from.

Thank you for the link redfred. I will take a look and see if this quenches my curiosity.

The question is really in two parts.

1. What is the concentration of OH ion at a pH of 10?

NH3 + HOH ----> NH4 + (OH)

pH 10 is the negative log base 10 of the H ion

p(OH) is the positive log base 10 of the OH ion

Therefore Log (OH) must be 4 and OH must equal 10000 mole solution or 588 meq

2. Conductivity balance requires that the sum of cations is equal to the sum of anions.

sum of cations_____sum of anions

The conductivity is a balance of 50:50 anions and cations.

What is 50% of the OH concentration as a contribution to the pHÉ. I know each ion does not contribute equally to conductivity but in this case 50% comes all from OH ion. or 588 meq. Therefore the conductivity will be 588 x 2 or 1176 . You do not state the temperature but I used 25 degrees C as it relates to reporting specific conductivity as a standard.

I stand to be corrected as all calculations are from an old memory bank.

Kevinm, Thank you for the explanation. I will hold my hand up and say that I don't understand anything that you have written - the issue is not with what you have written, the deficiency lies in my knowledge on this subject. Would it be to forward of me to ask you to explain this to someone with very little/ no knowledge?

For example :

• what does 588 meg mean?
• what would the resultant conductivity be in µS/cm

Yes I forgot to state that the conductivity was at 25^oC.

Thanks for taking the time to assist.

When ammonia is dissolved into water it will disassociate to form the ammonium (NH4+) ion and the hydroxide (OH-) ion. The formula is as given in my first comment only I indicated water as "HOH "and not the "H2O" you are more familiar. They are essentially the same but it better illustrates that water is H+ + OH- --->H2O. pH is a negative log in base 10 of the hydrogen concentration. It will range from 0 to 14. So if you want a pH of 10 that is the same as saying the inverse of pH or the hydroxide concentration called p(OH-). 14 - p(H+) = p(OH-). In your case a pH of 10 is the same as p(OH) of 4. (14-10 = 4). It is more direct to calculate OH- concentration than H+ concentration. If 4 equals log(OH) then OH concentration is 10000 . 1 mole of OH has an atomic weight of 1+16 or 17. So the mole concentration of OH at pH of 10 is 10000/17 or 588.23 equivalents or mg/meq. A Milliequivalent (meq) is 1000th of an equivalent or as reported mg/meq. If we assume that this is 50 % of the sum of anions and cations then the total dissolved solids (TDS) in the water is 1176 when added ammonia is at pH of 10. It is normal to take a portion of the TDS and normally 55% as a conductivity. I just don't have access to a "Standard methods book for the examination of water" . Elements do not contribute to conductivity equally and the book I believe has a factor for individual elements that can apply. The conductivity could be as low as 55% of 1176. I am a little shaky on my assumptions so if you have a Standard Methods Book or library access, do it to confirm. I feel the more I explain the more it complicates things especially if I am not up to snuff . So double check.

I have a new computer and haven't yet figured out all the math fonts. But conductivity is in umhos/cm or uS/cm as they are the same. Mu is indicated by me as "u" without the tail for now and uS/cm at 25 degrees C is standard now.

For Greek letters, select the Ω symbol in the menu bar above the posting window. This gives you several dozen special characters to choose from. You can also do subscripts, superscripts, boldface, italics, underlining, strike-through, and a few other effects. They don't seem to turn on/off as toggles, but you can select the text you want and apply the effect.

--Editor Crankshaft

Ευχαριστώ Ef-harist-O

It looks impressive/pretentious but ????

Thank you anyway.

??

You wonder how to do Greek characters; I explain; you respond with some Greek about consecrated biscuits, followed by the weird mistransliteration "Ef-harist-O."

That was definitely unimpressive, and equally pretentious. Or just plain goofy.

Please explain.

That is funny. I copied and pasted from a language translator. It is suppose to mean thank you in the Greek letters and the other letters are a rough pronunciation of the same. Biscuits? Pass the mustard.

Wow! Now we get into some etymology. Your Greek word (back translated) was "Eucharist." Hence my riff about biscuits (unleavened at that). Maybe it does simply mean "thanks"; I'll try to check.

Perhaps I overreacted to the word "pretentious." From time to time I am deliberately pretentious on, say, Amazon religion posts, but in this case I was just trying to relay a few menu hints that took me a while to figure out. Another thing I haven't yet figured out is how to do correct line/paragraph spacing on CR4. (There is another thread on this problem.)

As to the NH₃/H₂O question, I think we are in agreement. I apologize for anything else that may seem untoward.

I went through my math with a chemistist friend and he tended to agree with my numbers. However, I suspect I may be off be a factor of 1000 due to conversion. Max conductivity would then be 1.766 μS/cm and you could then be in the limits specified. Try the old hands on experiments with a few liters of the water and you should know in a hurry. You can get cheap test strips from www.mwater.ca for ph and conductivity. Good luck.

Kevinm,thank you for you patience and your assistance.

At what temperature? Conductivity is highly temperature-dependent!

Experimentation is the best solution to this problem.

At what temperature? Conductivity is highly temperature-dependent! - see post #16.

Experimentation is the best solution to this problem - perhaps, but since I did not know the answer I thought it wise to ask.