People overreact a lot these days. I'm sure you know someone who reacts to everything with extreme positions. Well, in the world of elements, that person would be sodium. It pretty much reacts violently with anything. Sodium justice will not be denied I vaguely recall dropping sodium into water as a high school student, but all of that memory is fairly hazy. I had to relearn.
I wanted to practice a little electrolysis, where I run a current through a solution and collect the cations on the cathode (positive terminal) and collect the anions on the anode (negative terminal). I had just a little sodium hydroxide available, and a really small evaporating dish, so a small experiment seemed quite possible. In fact, it was MUCH faster and easier (in some ways) than I ever imagined.
I dumped about 10mg of sodium hydroxide pellets into the dish and fired it to a melt within seconds with a blowtorch. Then I dropped a pair of nails (zinc galvanization sanded off) connected to my car battery charger into the melt. I was careful not to electrocute myself. I had the charger set on 12V/6A at first (vs. the 6V and 2A settings). I figured that 10mg would yield at most 5.1g of sodium, so this small scale experiment was plenty.
The first thing I noticed is that the NaOH made a really nice and bright yellow flame when fired directly. Yes, this is the sodium flame test. The second thing I noticed is that it tended to freeze while I got the nails inserted and the charger plugged in. The solid was not conductive enough to melt the NaOH. I needed to put the nails in and then give it a really solid boost with the blowtorch. Pretty soon the electrolysis took over and sustained the liquid solution between the nails. Electricity does not meander around the long way, so the NaOH remained solid around the edges of the dish away from the nails and the path between them.
I wasn't sure what to expect. Sometimes things take hours, but almost immediately the current meter was showing was 2-3A, I had a nice production of gas bubbling at the anode, and I could see pellets of silver liquid metal forming and then turning whitish around the cathode. When it really got going, the little pellets did more than turn white: they started exploding (like minor fireworks) and occasionally whizzing around surface of the dish. This was pure sodium reacting to air and some water formed at the anode. I had to back away and unplug the charger. I did not wish to have any burn me or react with my skin.
Note that it was raining in 80-degree plus weather as Tropical Storm Beta moves onshore nearby here. There was decent humidity in the air, at least 1% water vapor. The odds of me collecting any nearly pure sodium were low. I had a bottle with mineral oil and tweezers handy, but I was also photographing and occasionally trying to film. I was also a bit careful about picking the sodium out of the melt for fear of it reacting with the air. I managed to get a few drops into the oil, but most of it reacted more than I wished before I got it there. Still, I did get some photographs, some grayish partially-unreacted metal in oil, and a nice video or two. The one thing I never got was a video of it popping and sizzling around - I was more concerned with stopping this than filming it. I do wish I had a video record of that though!
What are the reactions involved?
At the cathode (+) nail, 2Na+ + 2e- -> 2Na
The sodium ions are reduced.
At the anode (-) nail, 2OH- -> H2O + 2e- + .5O2
The hydroxide is oxidized.
A further "reverse" reaction occurs: The Na that comes into contact with water creates the original ions and a little hydrogen gas.
Na + H2O -> .5H2 + Na+ + OH-
Here is the electrolysis is action. the cathode is on the left side. The whitish looking blobs near the cathode are pure sodium. It looked more silver in real life. If you look close you can see bubbling everywhere, ostensibly H2 gas and O2 gas and some water vapor. I can't really explain the blackish/gray collection around the cathode other than sodium formed here, presumably much of it in microscopic form. Much of it reacted with the atmosphere to turn back into NaOH, but clearly bits of it just disappeared back into the melt and cooled off. I'm not totally sure why the anode side and much of the melt turned yellow/brown. Maybe this is what the solution looks like when deprived of some but not all of its sodium. Perhaps there is some carbonate reaction occurring as well. It seemed a little darker than I expected.
This closeup shows it better, including the cooled NaOH on the sides.
Finally, here is what I collected below. It is really hard to photograph, and this is far from pure sodium. Each little drop I tried to collect turned to NaOH, some partially and some completely. None of it is mercury-like in all of its metallic splendor. Nonetheless, the grayish ones that are not fully reacted will still make a nice little reaction with water, I am told.
By the way, what is mineral oil? It is a by-product of refining that is made of carbon and hydrogen without oxygen. It is generally inert for collecting species of reactive metals and minerals and storing hydrated things like iron and opal without them oxidizing or dehydrating.
Here is my impure metal in mineral oil:
This was a quick and fairly easy experiment, despite the risks of electrocution, sodium burns, and fire. While I could have probably done better, I think it proved that NaOH really has sodium, electrolysis really works, and sodium is extremely reactive with air, water, and just about everything but mineral oil. This makes me wonder about the sodium ions in our diet, from table salt and other sources such as baking soda. That is some reactive stuff pulsing around our bodies somewhere. No wonder we don't want too much of it.
I assume the same experiment would work with potassium hydroxide. I'll have to look that up.
Thanks for reading,
Paul
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