Electrochemistry Ph of electrolyte (silver cell)

[mikeinkaty]

I keep getting a reading of 0.15 with my digital meter (Milwaukee MW101). Can that be right? I have ordered some Ph test strips to verify that reading.

But, what can I do to raise the Ph without effecting the quality of the solution? I've read that silver oxide can be used to raise the Ph but there was no explanation on how to do that? Do you just sprinkle the black powder into the solution? Also, most of what I've read has said the Ph should be in the 2.0-3.0 range but nowhere in the literature has anyone bothered to explain what to do to raise (or lower) the Ph. Knowing why this is necessary would be helpful also.

I did add 1/4 teaspoon of Tartaric Acid to my 3 liter electrolyte to see what that would do for crystal quality.

Mike

 

[goldsilverpro]

I've run large silver cells all my life and have never found a need to test the pH. Not once.

In my opinion, from your other posts, you have a tendency to get way too picky. This isn't rocket science. You just mix it up and run it. Works every time.

It's easy money. Why do you try to complicate it?

 

[mikeinkaty]

I was just responding to statements of others in that the Ph needs to be watched in an electrolyte solution. Should I ignore thoughts of all others in favor of yours? You don't seem to be able to respond to me without personal attacks and I find that very childish and rude, your chemistry knowledge not-withstanding. Is it ego gratifying to respond this way on a public forum? If you want to pick at me then go to a PM. That way I can at least delete it.
Mike

 

[Westerngs]

I tend to agree with GSP about pH except for one exception.

Bismuth is problematic in refining cells as it tends to plate out with the silver crystal. Controlling the pH of the electrolyte between 3 and 3.5 will keep the Bi from dissolving and it collects in the sludge in the anode filter bag.

For people that run a lot of mined silver through their cells, this is important, as Bi is often found in mined silver and the ASTM limit for Bi in refined silver is 10 ppm for 999 silver and 5 ppm for 9999 silver.

Other than that, I see no need to monitor pH.

 

[mikeinkaty]

I tend to agree with GSP about pH except for one exception.

Bismuth is problematic in refining cells as it tends to plate out with the silver crystal. Controlling the pH of the electrolyte between 3 and 3.5 will keep the Bi from dissolving and it collects in the sludge in the anode filter bag.

For people that run a lot of mined silver through their cells, this is important, as Bi is often found in mined silver and the ASTM limit for Bi in refined silver is 10 ppm for 999 silver and 5 ppm for 9999 silver.

Other than that, I see no need to monitor pH.

Thanks Westerngs, finally an explaination! I have been running fairly clean sterling that is fairly new so I may never find a need to bother with Ph. But I have run into problems with plateware that is old without really knowing what to do. Hence my quest for more knowlege.

Mike

 

[jimdoc]

I don't think that was a "personal attack", it was more like sound advice.

Jim

 

[goldsilverpro]

Sorry, Mike. I shouldn't have come on so strong. I know you're just trying to perfect your cell.

A pH of 0.15 would indicate a free nitric concentration of about 4.4%, if my math is correct. In my experience, I don't think that will cause any problems. However, since standard pH meters have big problems in that range, I doubt if it's accurate. I have an article about a mining company in Mexico that refines 120,000kg of Ag per month to 4 nines, and it mentions they operate with a pH of 1.2. You likely didn't utilize all of your nitric when you made up the cell solution. I notice you said you were dissolving the silver without heat. When the silver has dissolved, you could add some extra silver and then heat the solution to eliminate that last bit of free nitric, if the low pH bothers you.

If you do use silver oxide to raise the pH and, if the silver oxide is made by treating silver chloride with NaOH, make sure you first rinse out all of the NaCl with distilled water. You can test the rinse water for residual Cl- with a drop of silver nitrate solution.

These narrow range, 0-1.5 papers, are the only ones I know of that would even be close to being readable in that range. As you can see, the 1st increment is from 0 to 0.4

http://www.preiser.com/91-2581-02phpaperphrange0-15.aspx

 

[samuel-a]

Bi - a very bad element to deal with.
Probably the worst when it comes to pgm's (except the other pgm's) :mrgreen:

 

[solar_plasma]

I keep getting a reading of 0.15 with my digital meter (Milwaukee MW101). Can that be right? I have ordered some Ph test strips to verify that reading.

Though your problem seems to be solved by the great explanations,that also was interesting for me, - have you tried to test your pH-meter on standard solutions with known pH? That would be the first thing I would try. I guess you even could mix one by yourself using an analytic pure strong acid. Ofcourse a buffered one would be better.

 

[mikeinkaty]

I keep getting a reading of 0.15 with my digital meter (Milwaukee MW101). Can that be right? I have ordered some Ph test strips to verify that reading.

Though your problem seems to be solved by the great explanations,that also was interesting for me, - have you tried to test your pH-meter on standard solutions with known pH? That would be the first thing I would try. I guess you even could mix one by yourself using an analytic pure strong acid. Ofcourse a buffered one would be better.

Yes, I have tested it with everything and it is right on for anything above 3.0. The only thing i've tested below 3.0 is the electrolyte. I calibrate it before each use with the supplied solutions.

In answer to GSP statement, I don't see how I could have free nitric in the electrolyte after processing almost 120 ozt with it. After each run I scoop out the crystals and always have some remaining in the cell. Seems like free acid in the solution would have digested those crystals. The test strips should be here in a couple of days. I did drop that particular electrolyte as it was getting close to the end of it's life. I decided to not go the silver oxide route simply from fear of chloride contamination. I have a new batch filtering right now.

Mike

 

[goldsilverpro]

I keep getting a reading of 0.15 with my digital meter (Milwaukee MW101). Can that be right? I have ordered some Ph test strips to verify that reading.

Though your problem seems to be solved by the great explanations,that also was interesting for me, - have you tried to test your pH-meter on standard solutions with known pH? That would be the first thing I would try. I guess you even could mix one by yourself using an analytic pure strong acid. Ofcourse a buffered one would be better.

Yes, I have tested it with everything and it is right on for anything above 3.0. The only thing i've tested below 3.0 is the electrolyte. I calibrate it before each use with the supplied solutions.

In answer to GSP statement, I don't see how I could have free nitric in the electrolyte after processing almost 120 ozt with it. After each run I scoop out the crystals and always have some remaining in the cell. Seems like free acid in the solution would have digested those crystals. The test strips should be here in a couple of days. I did drop that particular electrolyte as it was getting close to the end of it's life. I decided to not go the silver oxide route simply from fear of chloride contamination. I have a new batch filtering right now.

Mike

I didn't make myself very clear and also didn't get the math exactly right. In essence, IF the pH is really 0.15, which is doubtful due to meter errors in that range, there would be about 0.708 moles of free nitric acid per liter. It might be interesting to make up a weak nitric solution of that strength - dilute 45ml of 70% HNO3 to 1 liter with distilled water - and measure the pH with your meter . Theoretically, it should be about 0.15 (I think), but I doubt if that's what the meter will read.
Antilog(-pH) = [H+] or [HNO3] = Antilog(-.15) = 0.708M

If your calculator has a log button on it: shift/log/-/.15 = .708

 

[butcher]

GSP I always though a log was what you set your head on when you wanted to take a nap in the woods. :lol:

I am not sure what to do with it even if my calculator had one.

 

[mikeinkaty]

GSP I always though a log was what you set your head on when you wanted to take a nap in the woods. :lol:

I am not sure what to do with it even if my calculator had one.

An Antilog is where you rest your feet, not your head! I thought everyone knew that! Mike

 

[mikeinkaty]

With my new electrolyte the Ph test strips turn dark red. My Ph meter said 1.3. So, I guess the meter is in the correct ballpark. I will test occasionally to see if it changes. I guess I'm good as long as it's between 1 and 3 ???

BTW - The factory support guy was really helpful and walked me through several tests. He said it was working fine. He did say the probe was good for only about 1 year of usage. No problems using it in AgNO3 al long as the probe tip was quickly washed with distilled water and not allowed to set around without being covered with the Ph4 test solution. He did say that there were correction charts necessary if the AgNO3 was made with de-ionized water.

Mike