pH sensors - how affordable?

Thread Starter

gapansi

Joined Nov 23, 2020
5
Hello everyone,

I came across the MiFlora soil measuring device from Xiaomi.

I saw that it claims to measure the pH levels of the soil together with moisture levels, temperature, and light. However, I was surprised to see that a pH sensor is usually double the price of the MiFlora itself.

Therefore, I was curious to know how MiFlora can determine the pH of the soil, but I could not find anything about it.

Do you guys know if what Xiaomi is claiming to sell is a bit of a scam or is there a way they can actually measure the pH with such a device?

Thanks!!
 

jpanhalt

Joined Jan 18, 2008
11,088
Some say a picture is worth a thousand words.

That picture disproves the adage.

Please give a link to the device. Remember this, pH is usually defined as a solution in water.* Thus, the surfaces must be wet.

*The actual definition does not require that. For example, the pH of pure hexane is quite high ... and usually irrelevant. It's just assumed to be a non-protic solvent.
 

Thread Starter

gapansi

Joined Nov 23, 2020
5
Here some links about the device: 1, 2, 3. I don't know if they help, I could not find much about the specs itself, that is why I was skeptical about the pH measuring part.

Please give a link to the device. Remember this, pH is usually defined as a solution in water.* Thus, the surfaces must be wet.
Then how is the pH of soil defined? And how is it measured compared to a solution?
 

jpanhalt

Joined Jan 18, 2008
11,088
I don't consider myself a "gadget-freakz"

Soil pH can be measured by a surface electrode that relies on the moisture in the soil to wet the electrode. You can also use other methods and bulb electrodes as well as indicator paper. NB: The latter REQUIRES water. I once knew a chemistry professor at a local small college. He was into being "green" and making his own biodiesel from leftover cooking oil. But, he couldn't get a decent pH with pHydrion paper (aka Hydrion paper)? DUH He ended up freezing the engine on his Mercedes.

If it is not water, then what does it matter? The pH of air is also quite high, but that doesn't make your skin dissolve.

I would consider the lack of technical information as indicative of a scam. It does have a "warranty." What do you have to do to get your money back?
 

jpanhalt

Joined Jan 18, 2008
11,088
How is this possible, when there is no oxygen present? What is the meaning of pH in the absence of water?
It's defined as the negative log of the hydrogen ion (H+) concentration. In hexane, that concentration is very low. Like I said, it can be defined, but it is meaningless for most purposes.

When you do go to non-aqueous, non-protic solutions, like sodium dissolved in liquid ammonia, we would refer to the pH as "very high." Still irrelevant for most purposes.
 
Top