Hello All:
Owl invited me to this forum via a common friend. I bring to the table a healty amount of scepticism and a few years teaching AP Chemistry in High School. I have a piece of paper that says I am a Chemical Engineer. I took and passed the Engineer in Training exam at the end of my University experience. All that and 50 cents might get me a cup of hot chocolate at a lot of places. I am still learning.
I have tried to get at the video mentioned, both with a browser and my FTP program without success. Size of file is not a problem to me as I have a *really fast* connection to the backbone of the Internet.
Electrolysis and batteries are subjects that first year College Chemistry classes never seem to get into in any detail. I know that my College classes did not even talk about it or I was asleep when they did - and I got good grades in Inorganic Chemistry. I have been looking at alternative energy for about 5 years as a way to keep my brain working after leaving the University.
What I know about electrochemistry has been gleaned from reading College Chemistry Textbooks and on the Internet.
I love the Periodic Table of the Elements. It tells so much. If there is interest I will post a treatise for understanding the table for the non-chemist. It might demystify a few things for some of you.
The metals all have electrons in excess of the previous Noble Gas configurations. They want to lose them to form Positively charged ions and the non-metals all have unfilled valence shells that are just a few electrons short of the next Noble Gas configuration and they want to get them and become negatively charged ions. Many of the atoms do a sharing between two or more atoms to form complex ions like Nitrate, Nitrite, Sulfate and Sufite. Each of those is a different ion even though they are spelled close to each other. The desire to gain or lose electrons to form ions is the basis of all most chemical reactions. Most of the rest is positively charged ions being attracted to negatively charged ions. A good example is Table Salt NaCl. Sodium metal is very reactive - it wants to lose an electron and is very eager to do so. A bit in water strips off a Hydrogen atom from water to form Sodium Hydroxide and liberate Hydrogen gas. It is so energetic that the Hydrogen Gas liberated has the energy to react with atmospheric Oxygen and go BOOM!. I did it many times in my classroom. Chlorine gas can kill you. Once Chlorine has gained an electron it becomes Chloride - a thing your body tolerates. If Sodium gets with Chlorine - Sodium Chloride is the result. This reaction is so energetic that it needs to be done behind a solid shield if any humans are around. The product is something that is essential to life - table salt.
In a battery there is one thing that has extra electrons and one thing that wants those electrons. These two are united by a substance that can carry ions and each is tied to a terminal. The terminals are used to allow electrons to flow from one side to the other during discharge or suck electrons from one side and inject them into the other side when the battery is charged. Cell voltage is given by the relative desires of the two items to gain or lose electrons. Oxidation is the loss of electrons while Reduction is the gain of electrons. Reduction occurs at the positive terminal of a battery and oxidation occurs at the negative terminal. Cell voltages tend to be pretty low and many batteries are groups of cells stacked up so that the cell voltages add. The standard car battery is such a stacked arraingement.
To illustrate a cell, consider the Vanadium Redox battery. It has been researched by a female Chemical Engineer at the University of New South Wales. Her name is Maria Skyllas-Kazacos. The web site for the battery is at
http://www.vrb.unsw.edu.au for those who want to look into it in greater detail. I use this as an example of a female scientist who is doing things that can change the world for the good of man. This battery can double the effective output of stream based electric generation systems and gives the Vanadium industry of NSW another market for Vanadium Pentoxide.
This battery is interesting becuase the only active things are Vanaduim ions on both sides of the battery. That is the beauty of it. We can talk about only one atom being Oxidized and Reduced. In the fully charged state, one side has lots of +2 Vanadium ions and the other side has lots of +5 Vanadium ions. The +5 ion wants to gain an electron to go down to the +4 (be reduced) and the +2 has an electron it will let you have so that it can go up to the +3 charge state (be Oxidized) if you want the electon badly enough. You have a battery if your desire to acquire an electron is greater than the other sides desire to keep it. The desires of many atoms and ions to gain an electron have been determined and are shown as voltages. They are shown on a table of Standard Reduction Potentials. The Metals all form only positively charged ions. If they gain an electron the value of your charge is reduced - thus Reduction is the gain of an electron.
When building a battery, you reverse the sign of the thing that is Oxidized (loses the electron) and add the potentials to give what your cell potential at standard states will be. The fun starts when you start using non-standard conditons. Stronger solutions, different temperatures. FUN!
The desire of atoms to gain or lose electrons is called electronegativity. The atoms on the periodic table have electronegativities. The non-metals have High electronegativities and the metals have low. That is why the metals react with the non-metals to form ions. Values of electronegatives have been determined and by compareing the two values you can get an indication of how strong the desire for the things to react with each other will be. In the case of ions, positively charged ions combine with negatively charged ions when the water is removed if they are soluable, or they come together and precipitate out of solution if they are not water soluable. I had my AP Chem students memorize a list of rules to help them on the AP Chem exam.
With regard to batteries, the energy needed to take away another electron from things has been determined and is expressed in terms of volts. This value is called the Standard Cell Potential. Returning to the Vanadium Battery, the V+5 gaining an electron and becoming V+4 is +1.00 volts. The V+3 gaining an electron to become V+2 is -0.26 volts.
Putting V+5 at one terminal and V+2 at the other terminal to give an oxidation reduction pair gives a theoretical voltage of 1.26 volts per cell. A fully charged cell will be all V+5 and V+2 and a fully discharged cell will all be V+4 and V+1. If there is nothing in the solutions that can "grab" any of the Vanadium ions and precipitate it out of solution, this battery should be able to be charged and discharged an infinite number of times. Since the charges are carried on ions in solution, there need to be some electrodes, say Stainless Steel or Carbon which just provide a site for the electrons to pass.
The interesting thing in this battery is the "Salt Bridge." This component must allow charges to equalize between the two solutions, but prevent the mixing of the solutions. Mixing the solutions is a *bad* thing. Some chemistrys generate so much Heat of Mixing that they can explode.
In the Vanadium battery, a mixing failure just produces a dead cell.
The people at NSW used Nafion - an expensive and strong Proton Exchange membrane. I wrote and have a small sample of it to play with. I am cheap or poor, take your pick. I think it can be done with gel filled tubes as salt bridges. A gel filled tube will allow charge carriers to pass, but should not allow mixing of the two solutions. A project I have on low burner is to prototype a home sized version of the Vanadium Redox battery that a homeowner could build, then write and sell a book about how to do it. Lead Acid batteries have a charge/discharge life span of a few years. People who are off-grid or grid-tied and generating end up spending a lot of money every few years for new batteries. A properly built Vanadium Redox battery should have an infinite life span with only minimal maintainence. I am noodlin on how to make stable components cheaply that will last for years...
I read the entire thread over the last two days. Some of it literally put me to sleep, my eyes glazed over and my head began to nod. I hope not to have that effect on you. I am accused of being long winded, but that is part and parcel of my teaching nature - put up with it!
I am noodling on the things that have been said, and there are a few things I need to spend some more time researching before I feel good about exposing my ignorance. Here is what I have gleaned so far:
AlaskaStar confirms that the fertilizer is Ammonium Sufphate
(I hate not being able to do sub and super scripts properly here hope this comes out properly)
This substane is an Ammonium Ion( +) with a Sulphate ions( -)
( NH ) (SO )
( 4 ) 4)
for a combined equation of NH4SO4
Fot this to be the final product, both ions need to be in the reaction vessels.
Sulfuric Acid gives the Sulfate ions easily obtained. It can be purchased at most any auto parts store. What Molar Concentration he is using is still an open question. How about it Alaska? Those in the know can purchase concentrated Sufluric Acid and dilute it down with DI or Distilled Water. I prefer to work with Distilled Water. In some ways I am a purist.
BTW - ON SOAPBOX
When mixing things, Always add the concentrated thing to the less concentrated.
In this case you would add Concentrated Acid being added to Water.
If there is an explosion, (think Heat of Mixing... look it up if you do not know what it is.) YOU will be covered in WATER with some of the acid. You might survive and be a little wiser as a result.
The BAD WAY results in you being covered with Concentrated ACID. You could be KILLED and would be standing at the Pearly Gates wondering what happend.
AWWW gee, do I have to do it that way? Acid to Water... YES!
OFF SOAPBOX
Two metals are used. Many metals could be used, but the comment about the hardware store eliminates a lot of them. I don't thing there will be any Vanadium here, so it was a good teaching tool that will not cloud the issue. You cannot find Vanadium at most hardware stores, unless they stock pottery supplies because Vanadium Pentoxide is a red powder used in coloring pottery... Naw...
For the water to come apart and produce Hydrogen reqires a voltage difference greater than about 2 or 3 volts. I kow that I am being pessimistic and that 1.42 volts is the book value for water dissassociation. My engineering training taught me that theroretical and actual are often not the same when it is put into practice.
If one of the metals is forming an oxide, it will steal the Oxygen from water resulting in liberation of Hydrogen gas. So it really has to want that oxygen...
How is the Ammonium Ion getting into the system? It must come in with one of the reacting species. What Ammoniates are used in construction?
That one needs some research.
For the metal that the acid is going to attack, Iron is a good one - easy to get and cheap. Ferric Sulphate or Ferrus Sulphate are easy to obtain. I think that one side of the battery is pretty much settled. Sulfuric Acid and Iron. The thing that is still out there is the other side of the battery.
Have I bored you you enough?
OgreOwner