PLEASE PLEASE HELP ME UNDERSTAND THIS ...

Thread Starter

seza

Joined Apr 5, 2017
2
Hi All,

Great forum, thank you to all who made it possible,

I conducted a simple experiment but I not able to understand/explain the results,

In large bowl full of material composed mostly of: FINE SAND + WATER + SALT(natural unrefined)
probably in equal parts which made it look like a paste.
I placed two electrodes: (+) GRAPHITE Rod and (-) MAGNESIUM Rod at various distance (D) from each other,
the multimeter reading across the electrodes was showing stable 1.5V no matter the distance (D)!!??

The next experiment - the same setup - I only covered up the electrodes with plastic wrap as in fully isolating each electrodes from the electrolyte (the material), I was surprised to get nearly enough the same reading (about 1.42V)!!??

Can someone please explain - preferably with some basic formulas what is happening here:

1. what do I have here: a BATTERY? a CAPACITOR? a GALVANIC BATTERY?
2. why is the distance between the electrodes not making any differences?
3. If this is a BATTERY of some sort - is there a theoretical way to estimate the energy stored therein?

Many thanks in advance.
 

wayneh

Joined Sep 9, 2010
16,769
You've made a battery. You measured its voltage, which is an intrinsic property that depends on the thermodynamics of the chemical reactions at play. It's nearly independent of scale, so you'll get the same answer no matter the size of the electrodes or their relative positions. (Within reasonable limits.)

The stored energy in your battery, on the other hand, is an extrinsic and scale-dependent property. Reactants will be consumed at rates that depend on surface area, concentration of the various reactants, temperature, electrode position, size and surface properties, and a zillion other variables. Current flow (amperage) will start at some level and likely decline over time as all these factors change. Electrodes foul, reactants are consumed and so on. So the stored energy is almost impossible to know any better than an estimation based on the starting details. An experiment would be more accurate.

I'm not sure I understand your experiment with the plastic wrap. It sounds like the electrodes were not thoroughly sealed away from contact with the liquid in the bowl.
 

kubeek

Joined Sep 20, 2005
5,744
electrodes have a set electrochemical potential, so there is no wonder the first case resuled in 1.5V every time.
In the second case with the covered up electrode, i suspect the plastic cover was either on water tight enough to truly isolate the electrode. If it was the very thing plastic baggie used for baked goods than I would not be surprised it was a bit leaky in the electric sense.
 

Tonyr1084

Joined Sep 24, 2015
5,680
Voltage measured is akin to electric pressure. Regardless of where you take the pressure reading (moving your electrodes around and even raising them up and down within the solution) the pressure (voltage) will measure the same. Where position and depth of penetration of the electrodes comes into play is in current delivery ability - or potential energy. The larger the rods and the more immersed the more surface area will give more amperage capability.

As for the plastic baggy thing: Back in high school - yes we had high school way back then - we did an experiment with two baggies and some fresh water and some salt water. In one baggy we put salt water and sealed it and immersed it in a fresh water bath. The other baggy was filled with fresh water and immersed in a salt water bath. We left them over night. The next morning the baggies filled with salt water were shriveled up while the fresh water baggies were bloated. Why? Osmosis. The passing of molecules through the plastic from higher concentration of salt to lower concentration. In other words, the baggy with salt water shriveled because the salt content was migrating through the baggy into the fresh water, turning it salty. The fresh water baggy had an influx of salt, thus bloating the baggy. I suspect the electrons were passing through the baggy because of some nuclear process where electrons were still able to transfer into and through the plastic baggy you put on your electrode. Keep in mind I said "I SUSPECT". I don't KNOW this to be the reason, I've never done that experiment. But maybe this explains what's going on and why you're seeing voltage despite the insulative property of the baggy.

As for the position and depth of the rods - you can have 1.5 volts and 200 mA or 1.5 volts and 200 amps. (exaggerated for effect) The voltage would still remain the same.
 

Thread Starter

seza

Joined Apr 5, 2017
2
Thank you all guys for your informative input,

does it mean that my electrodes esp the Mag will eventually corrode?

assuming that what will happen ... can the process be reversed by applying voltage (i.e charging the battery)?

grateful for your help.
 

#12

Joined Nov 30, 2010
18,217
One electrode will be etched to death. Trying to get the molecules to go back can be a problem because a lot of them wandered off into the soup.
 
Top