Understanding the nature of pH has bedeviled beginning (and not-so-beginning) chemistry students for nearly as long as chemistry has had students. It all seems so arbitrary, being the base-10 log of the inverse of hydrogen ion concentration and with a measurement range of 0 to 14. Add to that the electrochemical reactions needed to measure pH electronically, and it’s enough to make your head spin.
Difficulties aside, [Markus Bindhammer] decided to tackle the topic and came up with this interesting digital pH meter as a result. Measuring pH electronically is all about the electrode, or rather a pair of electrodes, one of which is a reference electrode. The potential difference between the electrodes when dipped into the solution under test correlates to the pH of the solution. [Markus] created his electrode by drawing molten antimony into a length of borosilicate glass tubing containing a solid copper wire as a terminal. The reference electrode was made from another piece of glass tubing, also with a copper terminal but filled with a saturated solution of copper(II) sulfate and plugged with a wooden skewer soaked in potassium nitrate.
In theory, this electrode system should result in a linear correlation between the pH of the test solution and the potential difference between the electrodes, easily measured with a multimeter. [Marb]’s results were a little different, though, leading him to use a microcontroller to scale the electrode output and display the pH on an OLED.
The relaxing video below shows the build process and more detail on the electrochemistry involved. It might be worth getting your head around this, since liquid metal batteries based on antimony are becoming a thing.
Was once a working chemist. The whole definition of pH and the general use of the “explaination” that “it’s easier this way” has always been frustrating. Anyone taking chemistry learns about concentrations of stuff. So saying [H+] = 10^-7 should not be confusing you’ve been using exponents for years already. How on earth it is “easier” to shorten that to “7” is beyond me. Like, are you paying to print stuff by the character or what?
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As a later in life ham radio lover the whole dB thing and the argument that “it’s easier to add dB than multiply stuff” is likewise ridiculous. I can add. But I can multiply also. I’m even pretty good at it after (checks notes…) let’s say numerous decades. It isn’t that hard. I’m not saying logs and dB themselves are useless, just that the argument that it’s easier the weirdass backwards archaic way never made sense to me. And seems to have confused the heck out of a lot of others as well.
Oh yeah also kinda a nitpick but definitely illustrates the point. pH doesn’t go from 0-14, strong acids at 10M are pH -1. Again dumb archaic and confusing. At least to me so much more obvious to just say [H+]=10M and leave it at that.
I don’t know much about PH or chemistry. My brother had a PH meter with a small glass sphere and apparently it was very expensive, and I think he had to replace it every 2 to 3 years. He used it for fertilizer concentrations in his greenhouse. Linearity is not a problem these days, as a simple uC can easily linearize things. Any Idea about accuracy and longevity of this thing?
A while back I discovered that the magnitude of brightness of stars are not powers of 10. The burden of historical cruft.
https://en.wikipedia.org/wiki/Magnitude_(astronomy)