Sciencemadness Discussion Board

Soviet glass electrodes

Mildronate - 30-7-2010 at 23:31

I found some soviet glass electrodes, can i make ph meter ? I put one of electrode in NaOH solution and conect it with voltmeter, but there was no power :(

psychokinetic - 30-7-2010 at 23:42

No power through the voltmeter, or no power to power said voltmeter?

Mildronate - 30-7-2010 at 23:46

Voltage was 0V

psychokinetic - 30-7-2010 at 23:49

Hmm. Being Soviet era, it may just not work.
It may not have been NaOh.

Or, we're wrong and you can't just use a voltmeter by itself.... not enough potential difference maybe?

Mildronate - 30-7-2010 at 23:54

I have4 different soviet glass electrodes. I will make some photos. I use different voltmeter diapozones 200mV, 2000mV, 20V. It wa NaOH :D and i can use voltmeter :P. :

Mildronate - 31-7-2010 at 05:34

Here is some photos:

[Edited on 31-7-2010 by Mildronate]

unionised - 31-7-2010 at 07:17

Massive mismatch of the output impedance of the electrode and the input impedance of the meter.

12AX7 - 31-7-2010 at 08:48

That's generally a good thing? It's my understanding that electrometer inputs are in the >10^12 ohm range, while the electrodes are perhaps 10^6ish.

If you mean the other way, that depends. VOM? Definitely. DMM? Somewhere between crude and good -- most DMMs are rated for 10M input, which will certainly have error, but won't necessarily short it out altogether. The cheapest pieces of crap are as low as 1M. Many have a "high Z" low range which is actually an open-circuit amplifier input; these are usually ">50M" or so, but may in reality be gigs or more.


matei - 31-7-2010 at 09:44

If the glass electrodes haven't been used for a long time they must be immersed in a conditioning solution (I think very diluted acid) for several days.
Anyway, from the picture I can't figure out whether what you have are only the glass electrode or a combined electrode which contains besides the glass electrode a reference electrode. In the former case (which was common in the past) you have to use a separate reference electrode (like a silver-silver chloride or a calomel). If your electrode is a combined one, you will have to fill the reference electrode compartment whith KCl solution (1M or maybe saturated, it depends on the electrode), because it has probably dried out during storing.

[Edited on 31-7-2010 by matei]

Mildronate - 31-7-2010 at 11:55

On some electrodes is writen colomel. i maybe can get soviet pH meter, where can i bay cheap electrodes if this stuf will not working? How can i know is this combined electrodes?

[Edited on 31-7-2010 by Mildronate]

[Edited on 31-7-2010 by Mildronate]

matei - 31-7-2010 at 13:06

I've took a closer look at your pictures and my bet is what you have are simple glass electrodes (the combined electrode has two inner compartments filled with solution and two silver wires inside). You'll have to use also a reference electrode in this case (a calomel electrode if you say you have one). Even though your electrodes have two electrical connections, only one of them is actually connected to the wire inside the electrode, the other one is only for grounding (shielding) the cable. Be sure to condition the glass electrode for several days as I already said, and also the reference electrode must be filled with saturated KCl solution and must be kept for some time in a saturated KCl solution, in order to moist the ceramic plug (diaphragm). You'll have to use at least an electronic voltmeter (they have a higher impedance) or a pH-meter in order to make measurements, and you'll have to calibrate the electrode with buffer solutions of known pH.

Mildronate - 31-7-2010 at 13:40

I will build something like this:

Mildronate - 1-8-2010 at 00:24

I cant open reference electrode to change KCL :(

matei - 1-8-2010 at 01:13

If it still has a solution inside, you don't have to change it. Just keep the electrode immersed in a saturated KCl solution for several days.
After that you can check if the reference electrode is working by making a simple electrochemical cell like this: take a beaker filled with concentrated NaCl solution, place an iron nail and the reference electrode inside and connect the nail and the reference electrode to the voltmeter. You should be able to get a reading on the voltmeter, which is the "open circuit potential" of the iron electrode (i.e. nail) in your solution.

[Edited on 1-8-2010 by matei]

Mildronate - 1-8-2010 at 01:47

I will try. How to test another electrode, the same way?

matei - 1-8-2010 at 02:43

Well, if the reference electrode works, than you can place both the reference and the glass electrode in a buffer solution (e.g. sodium acetate + acetic acid; a NaOH solution isn't such a good idea because the glass of the pH electrode is very thin and will be etched by the alkaline solution pretty fast; there are special glass electrodes which work well in very alkaline solutions) and measure the potential.

Mildronate - 1-8-2010 at 04:05

I will use this buffer solutions. Will be ok?

0.2M Na2HPO4 /mL |0.1M Citric Acid /mL |pH...
20.55| 79.45| 3.0
38.55| 61.45| 4.0
51.50| 48.50| 5.0
63.15| 36.85| 6.0
82.35| 17.65| 7.0
97.25| 2.75| 8.0

[Edited on 1-8-2010 by Mildronate]

matei - 1-8-2010 at 04:35

Sure, you only have to use 2 of them to calibrate the pH-meter, one for the acid domain and one for the basic. If you don't have a pH-meter which has a scale numbered in pH units and you use a voltmeter, the response of the glass electrode being fairly linear let's say between pH of 2 to 12, if you take 2 measurements of buffers of known pH and than plot the potential vs. pH you get a line (a "calibration curve") which allows you to obtain the unknown pH of a solution from the value of the measured potential.

[Edited on 1-8-2010 by matei]