[Siracuse]

(if my english is bad and/or technical terms are badly translated, I apologize in advance)

I'm having some trouble understanding some of the phenomena and the chemical reactions resulting from two laboratory experiments: the electrolysis of a copper rectangle(anode...that loses electrons, right?) and a steel nail(alloy of iron, cathode), and the other one being a series of tests using different electrolytes for spontaneous reactions, involving a carbon rod from a zinc-carbon commercial galvanic cell, or simply regular battery as the cathode, and two different anodes, one being of aluminium foil and the other one being the zinc cylinder from the battery.

The experiment procedures

a) Copper/Steel electrolysis

In this experiment, a solute of HCl with concentration of 1,0mol/L is used as an electrolyte, and is kept in a small 50ml glass container (called Beaker in english, I suppose). Next, the electrodes are put into the solute, making sure they aren't completely submerged in the acid. Afterwards, the electrodes are connected to a 9,0 Volt battery and a voltmeter. As soon as this procedure is done and all cables are connected, the electrolysis process starts.

The negative amperage starts to be measured, and it is soon noticed that it drops rapidly, but then slows down (it is verified later that the plotted data is close to a logarithmic function). Several reactions are being observed: the copper is constantly being corroded, and Cu(0) particles start to cover the steel nail, as expected.

Another reaction is observed: in the anode, bubbles start to appear, possibly hydrogen. But, also, another substance is observed to start sticking in the copper rectangle. It's white-colored, thin...it remains unidentified. Maybe a separate electrolysis process involving the ions in the solute and copper. Also, it is noted that the solute starts to adquire a faint-blue color. Very likely a small quantity of copper chlorate, as its solute also has a blueish tone. After the experiment is done, it is observed that the white substance starts to fall off, and deposits at the bottom of the container.

During the experiment, a very unexpected thing happens. As said before, the plotted data of the measured amperage matches that of a log. function. But at the later half of the experiment, the amperage starts to raise. I can't even think of a very rational explanation for this.

In summary, here's my doubts for a) :
-What are the chemical (half)-reactions involved in this experiment? I was expecting only one reaction to happen, but the experiment suggest that another reaction was triggered as well;
- What are the chemical compounds observed in this experiment? The white layer deposited in the container, the weak blue tone of the solute (which SUGGESTS presence of copper ions, but not entirely sure) and the bubbles (hydrogen gas, very likely);
-Why did the amperage raise? What, all of sudden, somehow, the concentration of the reactants raised in molarity or something? What's the meaning of this 


b) Spontaneous processes: unconventional batteries

Given a regular zinc-carbon battery, it's stripped for the sake of using its chemical compounds. More specifically,

- The carbon rod;
- The zinc cylinder;
- The "electrolytic paste", a combination of water, manganese oxide and ammonium chloride that acts both as a electrolyte and a electrode.

The latter two are used as electrodes, cathode and anode respectively. The paste is filtered to separate the ammonium chloride from the manganese oxide, to be used later as a electrolyte. The ammonium chloride solution is further dissolved with distilled water, and stored in another beaker. The zinc cylinder was supposed to be cleaned, to remove all electrolytic paste. I think a little bit of it was still inside of it...

Another two electrolytes are prepared, one being in a natural container that grows in trees. Yes, the lemon, or more specifically a lime in this case, where supposedly the citric acid is the electrolyte, a weak one. The other one is the previously used, contaminated solute of hydrochloric acid.

Don't ask why I used a contaminated substance for the experiment, I'll explain later. Well, the first tested "battery" is the lemon, using the carbon rod and the aluminium foil. A voltage is measured, ok. It is also tested if this battery can turn on a cheap, basic calculator. Success!

The second "battery" is the ammonium chloride and the same combo of electrodes. A voltage is measured as well. The calculator is turned on, but faintly. No idea if this was a systematic error or that the electrolyte had a very little concentration of ions in it.

A third "battery" is tested, with the contaminated hydrochloric acid and the same electrodes. This goes a little bit differently than the other two: aluminium and hydrochloric acid don't seem to mix well together (yes I did my research, both react very well). A volatile reaction is soon observed as you put the aluminium foil only, without the cathode, into the solute. Bubbles emerge, which are, again, probably hydrogen gas. It is observed also that a black substance starts to appear in the aluminium foil's surface. This remains quite a mistery, it's a substance with similar aspect of the electrolytic paste. No visible changes were viewed in the cathode. The same chemical process was observed in the anode with the "battery" actually working: a voltage was measured and it did turn on the calculator.

A fourth one is tested, being similar to the third in terms of observations, results and chemical reactions, but using the zinc cylinder instead as an anode.


Now, my doubts for b):

- The influence of the electrolytes in the spontaneous process. Does the concentration and/or the substance in use itself have an influence in the process? The experiment suggests that yes, it does, but I can't infer a good conclusion out of the observations. Organic compounds are supposedly bad electric conductors. The ammonium chloride "battery" had the weakest voltage of all four "batteries" tested. Both hydrochloric "batteries" were contaminated, so not much can be drawn from it;
- What exactly is the black substance formed in the anode of both hydrochloric "batteries"? I honestly don't know if that was supposed to happen, given that the solute was contaminated. Is it possible to determine what was that?
- Why was the carbon rod used as an cathode? It wasn't possible to remove all of the "electrolytic paste" that was stickied in it, so maybe that paste was the substance to be used as a cathode after all? Or was it just used to aid on conducting the electrons?


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I'm aware this is an quite enormous post. Be sure, however, that my interest here is to learn, not just to get quick answers. These are the observations that I'm stuck into, the rest (yes, there was more) was solved. The most I can do under those questions is speculate, but I'm not able to infer a solid conclusion with the avaliable theory (I'm using an Atkins). Yeah, maybe I'm missing something big here. 

As a side note, regarding the hydrochloric acid, if you wondered: the teacher told me to reuse the contaminated solute from the electrolysis in the galvanic cells experiment. I tried to ask her a couple times for another 1,0mol/L 'clean' solute, but she was obviously busy and a bunch of people around her. She had to monitor the other experiments as well, timing was running out...so yeah.