By Richard E. Bleil, Ph.D.
Electrolytes are just like regular elctros, but with one-third fewer calories.
Today, a student asked for my help in determining the concentration of electrolytes in water using electrical conductivity. To make his “solution”, he took a known mass of powdered metal and put it in water (three metals, actually: copper, zinc and iron).
So, I thought it might be fun to discuss electrical conduction. First, let’s discuss metals. We all know that metals conduct electricity in their elemental forms. Heck, this is why wires are always made of metal. On a sub-atomic level, the metals at the surface of the metal do an odd thing.
Electrons live in “orbitals”. You can think of them as apartment buildings, where pairs of electrons live together. It’s so romantical and shhhhhtuff. Now, electrons live in orbitals, but not all orbitals are occupied. At the surface of metals, these orbitals do a very unusual thing, and kind of merge. So, the surface of a metal is basically one large orbital, like a huge living space that all of the electrons share. This is why metals are shiny; the light bounces off the the electrons on the surface of the metal.
So, if you push new electrons into this merged mega orbital on one end, it will shove all of the electrons on the surface, creating them all to move in the direction of the incoming electrons. Hence, the electricity is conducted, but, as a bit of trivia for you, it only conducts on the surface of the metal. A larger wire has a greater volume and can absorb more heat without melting, but it’s only the surface that conducts. This is also the basis of a “Faraday cage”, which can be seen at physics shows where extremely high voltage electricity is arced onto a metal cage, while inside a person sits safely protected. If your car is ever struck by lightening, do not exit the car, because that charge will sit on the surface of the car, and if you step out, it will short through you. instead, drive the car and touch the surface to a bush or other nice conductor to discharge any static remaining on the surface.
If you make a salt of the metal (salts are simply ionic compounds of metals), you break this mega orbital. The orbitals are now in compounds and no longer free to merge, which means that salts, in and of themselves, do not conduct electricity.
Here’s an odd tidbit of which few people are aware. Pure water, I mean absolutely pure with no contaminants whatsoever at any concentration, does not conduct electricity. This seems counter intuitive to people when they first hear it, having been told to avoid water in electrical storms because, we are told, water does conduct electricity, but this is actually wrong.
The problem, you see, are these salts. They’re called “electrolytes” because, when dissolved in water, even at extremely low concentrations, they do conduct electricity. In water, these ionic compounds “dissociate” into ions, which are charged species (cations have a positive charge, and anions have a negative charge), and they travel freely and independently throughout the water solution.
Think of going to a party with your significant other. If you are at a place where you both are very comfortable, you both know people that you like at the party (and you’ve been together for a while), do you spend every moment together at the party? Most people would say “no”, but I don’t know you, maybe you’re very shy. Most people would “separate” from their significant other, and each would visit with their friends. They are at the party together, but they are free to roam.
Ions are like that. They are there in the solution together, but they separate and roam around independently. These ions are charged (positive and negative as I mentioned above), and it’s the charges on these ions that carry electrical current. Water does not have charge, so it cannot carry current alone, and in solid salts, the ions are trapped together, thereby canceling their charges, so solid salts cannot carry current alone either. But when you put salts (electrolytes) in water, the combination will carry current. (To the best of my knowledge, there are no other solvents that will allow ionic compounds to dissociate, so I believe that this is only true for water.)
It does not take much salt in water to dissociate and conduct electricity. This is the danger of water around electricity; the concentration of electrolytes in tap water, water on the ground, bottled water or any other form of water that is not very VERY highly purified, it will conduct electricity. This is why conductivity can be used to measure the concentration of salts at very low concentrations. The higher the dissolved salts (sometimes called “TDS”, or “Total Dissolved Solids”) the higher the conductivity the solution will be.
But, when a solute truly dissolves in a solvent, it will form a clear (but not necessarily colorless) solution. If you can see the particles, or if you get a cloudy mixture (like milk), it’s not a true solution because the solute did not truly dissolve. (The cloudiness is called the “Tyndall Effect”, and it is the reason that milk will eventually separate much like oil and vinegar are cloudy when mixed but will separate.) In their elemental form, metals do not dissolve in water. If they did, I wasted a BUNCH of money on my car. As might be imagined, the powdered metals in the water that the student used did not dissolve, and he could see the individual metal particles continuing to float around in the water.
But, the student did see a conductivity in the solution. This might seem odd, since the metal was not connected as needed to conduct electricity (like in a wire), and it did not dissolve. But, the reality is that oxygen is highly reactive. With the exception of gold, every metal exposed to air has a layer of metal oxide, and these metal oxides are electrolytes. Oxides are not “soluble”, but when something is “insoluble”, all it really means is that very very little will dissolve. Very very little, as we’ve discussed, is enough to conduct electricity for electrolytes.
Hopefully you’ve enjoyed this blog and learned something, but, honestly, I love this kind of stuff, and it’s because of this love that I wrote it! If you have a topic that you would like to learn more about, especially science or math but on any topic, feel free to let me know. I consider requests!