realflow100

yes apparently all you need is a simple salt bridge. not what I expected.

if you look back in a previous post i made (page 1) I used a piece of folded over paper towel draped over a 2-compartment container with sodium sulfate solution in each compartment with the solution wicked up the paper towel. with an electrode in each one and it seemed to work. created ph down to 2 and it seemed to behave as expected. though I only ran it at low current for a few hours. the design seemed to work well to prevent them from mixing about as effective as a clay pot. but much simpler and smaller-scale. I imagine it could of ran for longer and a ph of 1 would of been reached.

Yes they require high temperatures. charcoal. CO2. Sulphides. Dangerous gasses. which I could consider special processes requiring advanced equipment tools and additional compounds. It is much simpler to do the electrochemical separation method I described. with a porous material draped over 2 containers. and an electrode inserted into each container with sodium sulfate with a current applied. No high temperatures. No dangerous gasses or fumes. No charcoal. No sulphides. Additionally you get sodium hydroxide to use. and you can always undo it by recombining and mixing the two solutions back into one and get back the sodium sulfate. its reversible. The advanced version of the set up is just more efficient and robust and can produce a higher amount in shorter time.

Now I'm wondering if instead there would be some reason that sodium bisulfate would form first before true sulfuric acid. Essentially the concentration of sodium ions decrease over time gradually while the acidity increases. with an increase in the amount of hydrogen ions in the acidic compartment as well. but I dont know if the conversion to sulfuric acid would happen yet or in stages. where 1/2 neutralization of sulfuric acid point has been reached (1 part sodium to 2 part sulfuric acid)? I set up a more robust and more efficient version of the experiment. with a porous material sandwiched and sealed in between wide slots cut between two thin (rectangular shaped) containers to increase the surface area substantially and efficiency. in just a couple hours at 200mA current and about 3-4 volts. the acidic compartment reached as low as PH of 1. while the basic compartment reached closer to 13.5-14

Unless I've still completely missed something obvious. I don't understand.

Theres no driving force between them though with a salt bridge dividing/separating them from one another? I dont see how I could be missing anything. In my setup I didn't observe any sort of rapid neutralization between the two halves when the external supply was removed. They remained relatively stable even when sat for an hour while testing. the PH did not change significantly and I didn't observe any noticeable behavior at the salt bridge interface between the two compartments. unless your trying to explain that the "salt bridge" would need to be enormous in length or size or something? The two halves are not simply connected to one another directly. there is no easy path between them other than through the salt bridge. Think of a typical cell using a salt bridge setup like zinc and copper salt solutions. No reaction occurs between them automatically because the salt bridge separates their charges preventing them from mixing/reacting with each other. I don't see the problem with the setup.

Sodium sulfate would likely constantly be replenished at the salt bridge because as sodium hydroxide and sulfuric acid meet. they form sodium sulfate again. it could just be in an ever-tighter portion of the salt bridge as the concentrations rise?

I didn't really notice any rapid reactions at the porous separator I used. I could leave the solution sitting and not much would happen. The ph did not really start to change with any significance on it's own even when I left it sitting for about an hour. it didn't really seem to undo any of my progress. if there is any reaction it's probably quite slow. at least at these dilute concentrations. I imagine it might be more of an issue if someone tried to get higher concentrations. The thing is. if sodium sulfate does form from neutralization. it stops reacting because sodium sulfate itself is a neutral salt and doesn't react with either sulfuric acid or sodium hydroxide. so depending on the size of the "neutralized" portion between the two compartments. it might slow down and stop reacting after some time. leaving the bulk of the two solutions relatively unchanged. The way I set it up seemed to work as a fairly effective bottleneck in stopping or sufficiently slowing spontaneous reactions without an external force applied.

Sodium hydroxide is also conductive. so the reaction can "continue" proceeding without needing to occasionally add more sodium sulfate. while magnesium hydroxide is essentially nonconductive.

Possibly. it probably just depends if the sodium sulfate participates or not in whatever your doing with the sulfuric acid. and specifically what sort of concentrations your dealing with.

i started with a near-saturated solution. Not quite. to prevent precipitation from occurring too much. but I think if you wanted you could mix/stirring in additional sodium sulfate as the concentration of sodium sulfate decreases with further conversion to sulfuric acid/sodium hydroxide. I don't think that would be too necessary though if you only wanted a low molar concentration. (ph 1-2 is seemingly trivial to achieve even with a crude setup)

The thing is though. sodium sulfate is a neutral salt. and essentially doesn't react with sulfuric acid or sodium hydroxide directly. which is exactly what would be formed after any neutralization reaction essentially slowing down any neutralization after the sodium sulfate itself is formed. If we consider a 3 compartment setup. and used two salt bridges. the center compartment would have a relatively neutral mixture of sodium sulfate in it maintaining even further separation from the outer two compartments. Also depending on the construction of the compartments the efficiency and rate of diffusion of ions and the solution could be controlled. essentially if you first filled the middle compartment with sodium sulfate. then filled the outer ones with dilute concentrations of sulfuric acid and sodium hydroxide. no reaction would occur right away. even through there is a path of ions between the three solutions (the reaction would be very slow and gradual. occurring over time as ions and the solution gradually diffuses through the salt bridges. this could take hours or even days to run to complete equilibrium.)

Well it's at least been proven "potentially possible". Is there any ideas what sort of concentrations could actually be achieved with such a setup? With my "up and over" bridge it seems that the longer it ran. the more the ph would decrease in the acidic container and the more it would increase in the basic container. but I stopped at ph of 2 since it was getting late and i needed to sleep and couldn't sit up keeping an eye on it all night.

I tried creating a similar setup but without having access to a clay pot I decided on a different smaller scale setup. with just a pair of rectangular tall narrow containers. and a bit of folded paper towel draped across from one to the other allowing the sodium sulfate solution to soak through the paper towel from both containers.. I started with sodium sulfate in distilled water with a near-saturated solution. about 2M Added a pair of carbon plate electrodes. Started with about 1.5 watts of power. Oxygen and hydrogen evolution could be seen as small bubbles coming off of the electrodes. After about 12 hours the ph of the positive electrode side dropped to a very strong 2. while the negative electrode side increased to a very strong 13.5 Approximately 0.01M sulfuric acid concentration might be present in the positive electrode container. and I'm guessing that a similar concentration of sodium hydroxide might of formed in the negative electrode container It was confirmed that sulfuric acid was indeed created. I extracted a drop. put it on a slide and sprinkled a little baking soda on it. it immediately fizzed vigorously for about a second before stopping. releasing carbon dioxide. Indicating a clear neutralization reaction. The current flow or voltage required did not seem to change over time. both solutions remained conductive in the two containers. At 0.01M sulfuric acid concentration. there still remained 1.98 to 1.99M concentration of sodium sulfate. which is a very dilute concentration.

In the video. it is proposed that an aqueous solution of magnesium sulfate is put into the container and a micro porous clay pot (with no drain hole) is inserted. filled with a more dilute concentration of magnesium sulfate (presumably for initial conductivity) Carbon electrodes (or alternatively lead/lead dioxide) electrodes may be used. and inserted into the container and clay pot separately A voltage and current is applied. The negative being in the container. and the positive being in the clay pot to the electrodes Over several hours, potentially days, sulfuric acid is generated in the clay pot. while magnesium hydroxide forms in the container. There is still water in both the clay pot and container. that may need to be topped up regularly. The solutions that form are dilute. It proceeds slowly over time. This seems to be an inefficient way to do it though. and I'm fairly sure a more efficient and compact setup could be made. and I was wondering if sodium sulfate could be used instead of magnesium sulfate. Also I am not interested in concentrating to extreme hazardous concentrations. as that serves me no purpose. focusing more on the core idea and dilute concentrations.