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Author: Subject: Batteries are Friggin Complicated Yo (also voltage determination)
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[*] posted on 29-9-2020 at 07:47
Batteries are Friggin Complicated Yo (also voltage determination)


Preface: I actually have very little knowledge in regards to electrochemistry. I'd like to do some more analytical experiments with batteries, but I decided to start small here. The point of today's experiment was to measure voltage between two different setups and observe any differences.

Setup

4 beakers, 2 of which were 50 mL and 2 of which were 100 mL, were both filled with their respective volumes of water. Call the 100 mL set A and the 50 mL set B.

Magnesium Sulfate was then added to both sets of beakers in 10 gram portions for set A and 5 gram portions for set B to ensure equal concentration of the electrolyte solution in both sets.

Unfortunately, this is where I failed to be scientific and accurate in my little experiment. Originally, I wanted to use known metals for the terminals, but all I had were some copper and zinc coins lying around. Despite all my best efforts, I could not securely attach the coins to the sides of the beakers while immersing them in the electrolyte solution. I was forced to use a nail and screw of different but unknown metal to act as the terminals. The screw was bronze, and the nail was probably iron. Here is what the setup looked like:



First the 100 mL beakers were measured using a multimeter across both the nail and screw, and the voltage measured ranged between .3 volts to .4 volts. This was consistent across both beakers in set A.

Next the 50mL beakers were measured using the same nail and screw. Both beakers in set B showed a consistent voltage reading peaking at around .395 volts.

Before I come to my conclusion, there are a couple observations I'd like to make regarding the measurements.

O1) Each beaker was measured multiple times to account for variations in readings, but all readings were fairly consistent.

O2) The voltage in each beaker was noticed to peak at around .4 volts, and then suddenly drop back down again to a lower voltage, and slowly climb back up to the .4 volt mark after 2-3 seconds.

Conclusion

If the concentration of electrolyte is constant, then changing the volume of liquid will not affect voltage.

This might sound like an extremely obvious "no s*** you f****** d******" moment, however I think it will be useful in terms of deciding what volume quantities to work with in the future. Hopefully this means I can work on fairly small scales.

Questions

Q1) Did I make a battery? Can that be considered a battery? Or was I merely getting readings on my multimeter from some EM concept I don't fully grasp yet

Q2) Why did I notice the change in voltage over time as described in O2?

Thoughts/comments appreciated all ^^




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Tsjerk
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[*] posted on 29-9-2020 at 08:28


The volume of the electrolyte shouldn't make a difference in voltage, this will only correlate to the capacity of the battery.

Yes, you did make a battery.

I think the change in voltage comes from the bubbles made at the anode and cathode. They will make the surface of the electrodes smaller. That shouldn't matter in a perfect environment but probably does in this.
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[*] posted on 29-9-2020 at 09:26


Any two dissimilar metals in a electrolyte will produce a "potential difference" (voltage). An interesting experiment would be to use electrodes of as many different types of metals you can get your hands on, and different electrolytes. One can also take dissimilar coins and stack them alternately with a piece of electrolyte soaked blotter paper in between each layer. Each set of two coins is a "cell", and the stack is a battery.



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[*] posted on 29-9-2020 at 20:44


I would say that because open circuit voltage is a thermodynamic property of the system, that the varying voltage seems to be more likely due to contact resistances of the components.
In general, a higher resistance multimeter can sometimes help when measuring voltages with high resistances in series with the voltage source.
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