I am going to make some sulfuric acid through the electrolysis of a solution of copper sulfate (CuSO4 + 2H2O --electricity-->
H2SO4 + Cu + O2 + 2H2) and by taking advantage of how cheap it is to buy it and how copper does not really
react with sulfuric acid, (unless under special conditions) I am hopping it will work. But because of the strong oxidizing conditions, I need to have
an anode that will not corrode or react during the process. Any ideas (besides: platinum, lead dioxide(?), and maybe even gold...)?Hexavalent - 20-6-2012 at 09:50
What voltage current do you intend to use?BiOCl:BoatsInOutCrashLand - 20-6-2012 at 09:52
Somewhere around 5 or 6 volts... maybe more... it depends i guess.
[Edited on 20-6-2012 by BiOCl:BoatsInOutCrashLand]Hexavalent - 20-6-2012 at 10:10
Why not use thick carbon electrodes and filter out your solution when you're done?? 5 or 6V at a reasonable current will not erode them too
much....how much acid do you want to produce??
Are you doing this for the experience of doing electrochemistry or do you actually need sulfuric acid? If the latter, then NurdRage has a great video
on doing it using methods much better than here, or you can just buy a suitable drain opener from the hardware store. Look at the labels; some of them
contain up to 98%, 18M H2SO4.plante1999 - 20-6-2012 at 10:11
Carbon rod will corrode But contamination will be easy to removeMR AZIDE - 20-6-2012 at 10:12
Have you actually managed to purchase Conc Sulphuric, as drain cleaner in the UK, Hexavalent.??
If so, what were the products.....???
BiOCl:BoatsInOutCrashLand - 20-6-2012 at 10:22
If I try to filter the solution, can't it absorb the water molecules from the filter (unless it's very dilute)? I am doing this for the experience and
i plan to use it for a few experiments that i'm planning.plante1999 - 20-6-2012 at 10:34
filter the acid before boiling it. THexavalent - 20-6-2012 at 11:41
Mr Azide
This stuff I bought from a local building supplies company, but I imagine it can be purchased at hardware stores;
The label on my bottle specifies 97% H2SO4.Hexavalent - 20-6-2012 at 11:44
Yea, as plante1999 said you can just filter off the any small carbon bits that break off the electrode.
Filtering it will not dilute the acid in any way....if you feel confident, you can boil down the acid to concentrate it....but I would not advise it,
certainly not to someone with little experience such as yourself. If you want more concentrated acid, I would recommend simply purchasing it as I
mentioned above.BiOCl:BoatsInOutCrashLand - 20-6-2012 at 13:12
My plann is to have a higher concentration of the copper sulfate (not too much though) to have a higher concentration of the acid (that way i do not
need to boil it down).Hexavalent - 20-6-2012 at 13:46
At 5-6V, conversion time for concentrated copper sulfate solution to sulfuric acid is going to be quite long, and even then you may need to boil it
down.
BiOCl:BoatsInOutCrashLand - 20-6-2012 at 14:42
Well i do not need it to be too concentrated for my needs and if the process is going too slowly, i will use a higher voltage...maybe 9. bob800 - 20-6-2012 at 15:56
<s>I just calculated that this method is capable of generating acid of no higher than 1 M concentration, but this seems a bit low. Could someone
please double-check my work?</s> -- [EDIT -- OK, found my mistake. 9% seems more reasonable]
CuSO<sub>4</sub> becomes saturated in water at 320 g/ 1 L (anhydrous, @STP)—that's a 2 M solution. Assuming that this reaction proceeds
with 100% efficiency and to completion, 2 mol of CuSO<sub>4</sub> will form 1 mol of H<sub>2</sub>SO<sub>4</sub>:
So the 2 M solution of copper sulfate is now a <s>1</s>2 M solution of sulfuric acid in water—<s>98 g/
L</s>196 g/ L, or roughly <s>9%</s> 20% concentration.
[EDIT: 2nd equation was completely unbalanced. See next post for correction]
[Edited on 21-6-2012 by bob800]vmelkon - 20-6-2012 at 17:29
9%? That's pretty weak.
Personally, I get my H2SO4 from old car batteries. Some people abandon them or you can visit certain garages (they leave the old ones outside). Just
connect them to a battery charger for 1 day just to make sure it makes as much H2SO4 as possible. The conc never reaches the same as a new battery.
I'm in Canada and there aren't hardware stores that sell H2SO4. They are all NaOH + sodium metasilicate.barley81 - 20-6-2012 at 17:35
In a 2M solution of copper sulfate, there are 2 moles of sulfate ions per liter. If only one mole of sulfuric acid were formed per two moles of copper
sulfate, where would the extra sulfate go? It's a 1:1 ratio between copper sulfate and sulfuric acid, and you would get 196g sulfuric acid per liter
of solution (roughly 20% concentration)bob800 - 20-6-2012 at 19:30
In a 2M solution of copper sulfate, there are 2 moles of sulfate ions per liter. If only one mole of sulfuric acid were formed per two moles of copper
sulfate, where would the extra sulfate go?
Ah, you are correct! My second equation is only balanced electrically (there's more sulfate on the left side than the right, as you pointed out). It
is a 1:1 ratio:
2 SO4 + 4 H ---> 2 H2SO4
in which case you are correct about the 2 M acid. I guess this method isn't quite as bad as I originally thought!electrokinetic - 20-6-2012 at 20:05
Funny you posted this, I'm doing the same thing except my goal isn't to get sulfuric acid, it's just to do some copperplating. Here's a couple of
things I found out.
First, you can always dissolve more copper sulfate. Those calculations are based on starting with a saturated CuSO4 solution but there's no reason
you can't keep it saturated. I kept adding CuO or copper carbonate because I didn't want the pH to get too low.
Second, when the pH gets low enough, hydrogen will start evolving at the cathode even with copper ions present. I know there's some equation that
explains that, but I'm too lazy to look it up right now. All I know is, I came in after having it going all weekend and no matter how low I turned
the voltage I couldn't keep hydrogen from evolving.
BiOCl:BoatsInOutCrashLand - 20-6-2012 at 21:54
@barley81-Yes, I began to wonder that also. @electrokinetic- I was planning to supper saturate my solution originally...but now that i think of it,
the copper sulfate will most likely recrystalize during the procces...keeping it saturated may be a better idea... the hydrogen gas may be the
electrolysis of the acid i am guessing...
Okay, so now I have finished a few calculations on how long the electrlysis proces may take... it wil take three days (at 9 volts) to make one mole of
the acid (but instead of using a molar solution, I will be using just enough water to make a saturated solution of one mole of copper sulfate). But of
course the the proces is not 100% efficient so there will be liess than the expected yield...but as long as i add a bit more than a mole it still may
be able to reach the expected yield... I think I will try what electrokinetic did another time...
[Edited on 21-6-2012 by BiOCl:BoatsInOutCrashLand]AJKOER - 22-6-2012 at 07:00
Compare the product results above with mixing Oxalic acid (usually available as a dihydrate) and CuSO4 and filtering:
Obviously, dissolving the CuSO4 creates even further dilution requiring the final Sulfuric acid product to be concentrated. See the thread "Using
Oxalic Acid to Make H2SO4,..." at http://www.sciencemadness.org/talk/viewthread.php?tid=18963
Copper oxalate is an interesting salt as upon heating it in an inert atmosphere liberates Cu, but in air stream for some 2 hours, produces a very fine
CuO with a high surface area (useful for catalytic purposes). See: "Copper Oxalate synthesis and decomposition" at http://info.tuwien.ac.at/struchem/files/poster_cuox.pdf BiOCl:BoatsInOutCrashLand - 22-6-2012 at 11:30
Thanks for the idea AJKOER! I will try that some day...
If the pentahydrate is used... CuSO4.5H2O + 2H2O --electrcity--> H2SO4 + 5H2O +
Cu + H2 + 2O2... meaning that there will be 5 moles of extra water in the final products (not including the water that did not
come from the pentahydrate). On that note, is it possible to heat the pentahydrate to drive of the water molecules without it decomposing? If so, how
should it be heated?
[Edited on 22-6-2012 by BiOCl:BoatsInOutCrashLand]
