Sciencemadness Discussion Board

Electrolysis of potassium soap?

HellstormOP - 9-2-2012 at 12:32

recently I've tried to electrolyse very concentrated and hot potassium soap with very little water in it in an effort to generate potassium metal. I took a special, yellow-brownish and very sticky semi-solid potassium soap, which contains additional potassium carbonate in it, and according to the label, has a pH of 10-11. Then, I microwaved a small amount of it, until it was boiling hot and started to foam. I took a laptop's power supply and connected it to two wires, where I removed the insulation at the other end, and then I placed the wires into the still hot soap, which had the consistency of liquid honey. However, nothing actually happened! There was hardly any bubble formation at the electrodes, although the power supply definitely was plugged in.

I'm wondering why this electrolysis didn't work, as soap actually consists of salts of potassium and fatty acids, and thus should undergo electrolysis when molten. Also, there was potassium carbonate dissolved in it, which should have been electrolysed either.

Mr. Wizard - 9-2-2012 at 13:02

How much current were you able to push through the molten solution? Liquids only conduct if they have something to move the electrons or charged ions. It may be that at that temperature there are no K+ ions, just molten covalently bound potassium and the acid soap (stearate, palmate ?? )

Laptop power supplies are often set up not to deliver voltage and current unless it meets certain parameters, such as a signal from the computer that it is 'ready'. I have an Apple G3 laptop power supply that won't even show any voltage unless it gets the correct signal from the computer. This made it very exasperating to trouble shoot, and I bought another power supply, only to find it wasn't the problem. Check it with a meter to see if it has voltage. Use a small light bulb, or an ammeter to measure if any current is flowing through your molten solution.

HellstormOP - 9-2-2012 at 13:22

Well, I currently don't own an ampmeter. However, I noticed that the supply has a short circuit protection, as it automatically turns off (green LED goes dark) if short circuited. Thus, it already shows voltage if it is just plugged in.
BTW: The green LED didn't go dark as I put the electrodes into the hot soap, thus, the short circuit protection did not kick in.
AFAIK, soap always comprises ions and no covalent bond between the alkali metal and the acid rest. Also, there was potassium carbonate in it, which should have been electrolysed, as it was dissolved in the molten soap.

Mr. Wizard - 9-2-2012 at 19:04

OK I see your situation. With some very simple equipment you can experiment to see if the liquid conducts current, and most likely ionized. Take a very small light bulb (mains voltage) in the area of 1 to 15 watts that will operate from your mains, and set the light bulb up in series with the molten liquid, using a couple of nails or bare copper wires as the electrodes. If the liquid will conduct, the bulb will light up. The bulb serves two purposes, indicating current flow, and limiting current flow to a safe amount. Be careful, as the full voltage of the mains will be on the wires. This will not yield any K, but just demonstrate the ability to carry current. To do electrolysis the current must be rectified, or converted to pulsating DC with a diode. A diode can be a cheap one that will handle the current of your bulb, or can be fabricated from a sodium bicarbonate solution with a lead sheet and an aluminum sheet. This link demonstrates the construction of the DIY diode.

Once again, the voltages on these wires and in the liquid can kill you. Most know this, but if you don't, here is the warning.

Bonee - 20-2-2012 at 12:15

hmm did you even calculated the amount of potassium in the mix?
i think the molten mix catch fire even before you provide enough energy to liberate free potassium ions

the electrolysis of potassium carbonate need some very high temperature and you are dealing with a 90%+ organic liquid

497 - 20-2-2012 at 23:39

Make some ethylene/propylene carbonate, then it might actually work. I think KI may be soluble enough in them. Or AlCl3 complex of KCl will definitely work.

HellstormOP - 1-3-2012 at 02:45

@Bonee: Apparently, the K2CO3 is dissolved in the soap, as it appears transparent. Thus, the K+ ions are already liberated.
Also, it is possible to use ionic liquids (low-temperature molten salts) to produce even alkali metals by electrolysis, and a molten soap at least hypothetically is an ionic liquid.

[Edited on 1-3-2012 by HellstormOP]

HellstormOP - 1-3-2012 at 04:20

@497: Can I use acetone instead? It is polar-aprotic, thus it should be able to dissolve both the K+ ions and the large, non-polar fatty acid ions. It is also substantially cheaper and easier to obtain than ethylene/propylene carbonate.

HellstormOP - 2-3-2012 at 03:38

Nobody has got any othe ideas?

HellstormOP - 3-3-2012 at 09:31

Another question: When I heated the soap to remove any residual water, the water bubbled oujt but the soap still was very viscous. Can ions sufficiently move in relatively viscous fluids, when there is enough voltage?

bbartlog - 3-3-2012 at 10:19

If you are actually trying to obtain potassium metal rather than just examine the current carrying capacity of various types of molten potassium compounds, you will need to do something else. Elemental potassium will react with any of the melts that you have proposed. There are only a few solvents that have any chance of working (see what 497 has posted, above), and just randomly proposing possibilities (acetone won't work) is a waste of time.

HellstormOP - 3-3-2012 at 10:27

Why should acetone not work? And why should potassium metal react with the fatty acid ion?

HellstormOP - 4-3-2012 at 13:56

Can ions sufficiently move in relatively viscous fluids, when there is enough voltage?

HellstormOP - 8-3-2012 at 00:55

Yesterday I tried to find out if that soap is electrically conductive if it is heated/molten. I firstly heated the soap until the water was fully evaporated (firstly the soap assumed the color and consistence of pudding, apparently because of the micro-sized water bubbles and potassium carbonate crystallizing out. Then, it turned hard and brittle. Apparently, potassium soap cannot be molten using a normal electrical kitchen heating plate. Also, I've found out that a small amount of water is necessary so hat the potassium carbonate can be dissolved in soap.), and then used my recently purchased ampmeter to measure the resistance. The ampmeter showed a resistance of 1 MOhm. I placed the soap in an almost air-tight container, for later experiments.

Little_Ghost_again - 16-10-2014 at 06:18

Potassium soap is made with potassium hydroxide, instead of sodium hydroxide as in normal soap.
I cant see this working but then again I am a noob.
In theory there should be almost none of the potassium hydroxide in the soap after it has saponified or iy would be caustic.
The idea when making soap is to use all the hydroxide up in saponifaction.
The term potassium soap is a bit misleading. Its like calling normal soap sodium soap. So I am guessing the only potassium in there is from the carbonate.
Thats about all I can tell you. Apart in 99.99% of all cases liquid soap is made with potassium hydroxide and 99% hard soap sodium hydroxide. When you make the soaps you try and make sure that all the hydroxide is used up in the reaction with oils.
So a cleaner start point would be the just use the carbonate, Although your pH seems high to me for soap