Sciencemadness Discussion Board

VERY strange electrolysis results?

jgourlay - 26-7-2008 at 13:17

Doing the electricity + water = H2 and O2 thing. Primitive setup: all containers are plastic water bottles, water is tap water with a pinch of baking soda, wire is ancient rubber insulated copper. 20Vdc.

Instead of getting each wire bubbling gas, the "com" wire is bubbling gas as expected. The +V wire is shedding this milky white precipitate that is liquidy and heavier than water. What gives?

chemkid - 26-7-2008 at 13:52

Were scientists not fortune tellers...having so many bad apparatus components gives huge variety of possibilities. But it should be a pretty simple fix...use the scientific method and change things until the results change.

Start by replacing baking soda with salt, as salt is a better electrolyte. Does that give the expected results?

Next, replace the plastic with glass, how about now?

Now replace the wire with new wire and immerse only the copper part in solution? How about now?

Now use distilled water, how about now?

Seriously, get some apparatus even simple changes like using a measuring cup instead of a plastic water bottle and salt instead of baking soda will greatly improve your science rather than having every experiment turn into an experiment to find out whats no going as expected.

Chemkid

[Edited on 26-7-2008 by chemkid]

jgourlay - 26-7-2008 at 14:12

Wow...that was helpful. I used baking soda instead of salt because several sites online recommend it. As for the rest....if I could use my wife's glassware, or just pop on over to walgreens and pick up a hoffman apparatus, I would.

ShadowWarrior4444 - 26-7-2008 at 18:11

The plastic containers should have no effect on the reaction, so one must consider the possible ions in solution and the composition of the copper pipe.

The anode was the one giving off the precipitate, so it was an oxidation product. Copper pipes are not pure copper; they are generally recycled and may be alloyed. Perhaps it contains tin or zinc which would provide a milky white hydroxide precipitate.

When presented with the problem of finding an unknown chemical, you should look at all possible elements present in the reaction and what compounds of them have the properties you're looking for. Secondarily, examine the conditions those compounds are said to form under, and any tests you can perform for them.

BromicAcid - 26-7-2008 at 18:37

Quote:
Originally posted by jgourlay
The +V wire is shedding this milky white precipitate that is liquidy and heavier than water. What gives?


Okay, some clairification here. You say it's a precipitate but that it's liquidy, so is it really a precipitate? When electrolysis is discontinued do you end up with any noteable amount of solid settled on the bottom of your container? (Anything you could recover?) Additionally, distilled water really would help eliminate the possibility of side reactions and simplify matters, you can buy it from most any grocery store or pharmacy in the drinking water area. Barring that just tell us about your water, it's tap you say, but it's not well water or anything is it? Is it hard water?

Electrolysis is notoriously slow and although you might be seeing something coming off your electrode the amount generated is likely incredibly small so impurities in your water could be at fault. Finally, you mention the voltage but what about the current? How many amps? At high amps many strange reactions can occur so that could also help matters.

Chemkid was right in that there are a number of variables here, things are so much easier to see things in person, but all we have to do is take our time and ask the questions that are relevant and eventually we will have enough information.

My current guess is that you have hard water, there are some calcium ions floating around and you're oxidizing the water to give peroxide and peroxycarbonates which are generating insoluble salts with the calcium. But that's just a shot in the dark, looking forward to your response.

[Edited on 7/26/2008 by BromicAcid]

not_important - 26-7-2008 at 22:40

You don't even need hard water, processed water commonly has traces of Ca and perhaps Mg in it, added intentionally both for keeping the water alkaline and for health reasons.

As already stated, a small amount of precipitate can seem rather voluminous as it drifts down off an electrode.

And also as already stated, try using deionized/distilled water. With alkaline electrolytes, nickel or stainless steel electrodes are the best cheap material.

Don't use NaCl if you're after O2, you'll get Cl2 plus sever corrosion of most easily accessible electrodes.

Klute - 27-7-2008 at 05:42

Did the white component start appearing immeidatly at the beggining of the electrolysis? Or was there so kind of induction period?

Depending on the plastic, isn't possible some plastifiers get into solution and precipitate as it is oxidized to a polymer or a large mw carboxylic acid?

jgourlay - 27-7-2008 at 06:31

Guys, thanks for the responses. Chemkid, sorry I was testy with you: I was just frustrated. The first, and last, time I did this I was about twelve, had an even crappier setup, and it worked gangbusters. I'm supposed to be showing this to a bunch of little kids this week so....

Okay, I left this running overnight. The "precipitate, is some kind of bluish copper compound: evidently from the wires. It's milky blue, roughly settling at the bottom but also dispersed through the liquid.

The water is houston water. I don't think it's hard, at least not by the standards of where I grew up. I need to do some more research to figure out how to make this work...

Weird thing is that I did this as a kid, and our water unbelievably hard....

chemkid - 27-7-2008 at 07:11

I was a little testy myself, I apologize.

woelen - 27-7-2008 at 09:31

With copper wire as anode you'll get oxidation of the anode and hardly any (if any at all) gas is produced. The light blue material you get probably is copper carbonate, or some basic copper carbonate.

If you do the same experiment with sodium chloride, you don't get chlorine at the anode, but a brown/yellow slimy precipitate of Cu2O/CuCl mix, which becomes flocculent after some time and mnay darken to a deep green/brown.

If you really want oxygen at the anode, then use a graphite rod. With sodium bicarbonate as electyrolyte you will get a mix of oxygen and carbon dioxide. With sulphuric acid or sodium hydroxide you will get oxygen. With sodium hydroxide, you also get oxygen at the anode when you use a copper anode.

To my opinion, the use of plastic beakers is perfectly suitable in this experiment, especially when simple sodium bicarbonate or table salt is used. These will not corrode the plastic.

12AX7 - 27-7-2008 at 11:37

I'm not sure graphite will stand up to oxygen real great. In sulfuric acid, it swells, and it probably turns into whacky things in base as well (I don't think I've tried). Stainless steel is suitable in NaOH though, and that's easy to come by.

Tim

ShadowWarrior4444 - 27-7-2008 at 12:56

Quote:
Originally posted by 12AX7
I'm not sure graphite will stand up to oxygen real great. In sulfuric acid, it swells, and it probably turns into whacky things in base as well (I don't think I've tried). Stainless steel is suitable in NaOH though, and that's easy to come by.

Tim


This is quite true, graphite is unsuitable for water electrolysis because it can be oxidized and is not as structurally stable as a metal. You will likely see the anode slowly disintegrate into black powder.

In strong base, carbon is electrolytically oxidized to various organic compounds, such as mellitic acid. (There's a thread on that floating around here.)

Anything resistant to oxidation will serve as a useful anode; however anything but platinum will slowly degrade.

not_important - 28-7-2008 at 05:06

Quote:
Originally posted by Klute
Depending on the plastic, isn't possible some plastifiers get into solution and precipitate as it is oxidized to a polymer or a large mw carboxylic acid?


If you stick to bottled drinking water or juice containers, which are almost always polyethylene terephthalate (PET or PETE, recycling code #1), or clear disposable cups, usually polystyrene (recycling code #6) or poly(methyl methacrylate) (PMMA, no unique code), you'll not have plasticisers to deal with.

Polyolefins , milky translucent plastics, polypropene (PP, code #5), Low density polyethylene (LDPE code #4), High density polyethylene (HDPE code #2 - tupperware & milk jugs), also generally don't have plasticisers added when used in products intended for contact with food.

PETE is not good for contact with hot alkaline solution, or storage of basic solution in general. The same is true to a lesser degree for acrylics; in that case the alkali just removes the alcohol side chain leaving carboxylate groups that can interact with the solution, while with PETE the ester backbone is attacked leading to disintegration of the container.

jgourlay - 28-7-2008 at 05:54

Okay gents, thanks for the replys: I'm getting warmer. Last night I tried it again: NaCl with nails for electrodes. Obviously the copper is still in the water but somewhat protected by the nails.

Lots of one gas which I haven't tested yet (hydrogen?), none of the other, and oodles of brown goo (ferric chloride? Iron Oxide?).

Here's what I have I can use as electrodes, I'll let you all pick, and again I'm trying to get both hydrogen and oxygen, preferably without some third party something. Also, let me offer this: I've bandied about for years getting a variac for some other non-chemical experiments. I could be persuaded to do that, get a bridge rectifier and some caps, hook that mother up to 240vac and obviate the need for electrolyte.

1. Copper Wire.
2. Nails.
3. Some old gold chain, probably 10k trashy although I may have some 18K laying aroud.
4. Fine silver.
5. Soldering wire.
6. Pencil lead (does that count as graphite?) I can wrap some chopsticks in tinfoil and cook them redhot over coals to make charcoal--if that would work.
7. Nickel
8. BeCu
9. 303 stainless

Here are my electrolyte choices.

1. Sulphuric acid: I'm real hesitant here as my "lab" is the kitchen counter next to coffee point, so it would have to be so dilute that if a 3 year old tumped it over, she wouldn't get hurt. Hmmm...that lets out a 240volt power supply, too.

2. NaOH
3. Baking powder/soda
4. Vinegar
5. Borax
6. Salt
7. citric acid.

not_important - 28-7-2008 at 06:10

I'd go for the nickel, if you mean actual nickel or high nickel alloy and not the US coin. Stainless steel 2nd, nails or other low grade steel or iron alloys 3rd. Gold would be good if alloy and not just plated, the plating is often so porous that you might as well use the base metal by itself.

With iron, steel, or nickel electrodes, go for the alkaline electrolytes - NaOH, Na2CO3 (washing soda), NaCO3 (baking soda, not baking powder). Acids and halides - NaCl - will result in corrosion of the electrode instead of oxygen generation.

jgourlay - 29-7-2008 at 06:48

Would it help if where I wrap the electrode with wire I were to dab on some silicone so the copper has not exposure to the water?
Quote:
Originally posted by not_important
I'd go for the nickel, if you mean actual nickel or high nickel alloy and not the US coin. Stainless steel 2nd, nails or other low grade steel or iron alloys 3rd. Gold would be good if alloy and not just plated, the plating is often so porous that you might as well use the base metal by itself.

With iron, steel, or nickel electrodes, go for the alkaline electrolytes - NaOH, Na2CO3 (washing soda), NaCO3 (baking soda, not baking powder). Acids and halides - NaCl - will result in corrosion of the electrode instead of oxygen generation.

woelen - 29-7-2008 at 10:58

Yes, that would be a good thing. I actually made an electrode from a short platinum wire, where I melted the platinum wire in glass and made the connection with the copper wire inside the glass rod, such that only the platinum is exposed to the liquid.

The only problem might be that the silicone also is going between the electrode and the wire, so another cheap option may be to use some tape around the copper wire and then use some hardening glue, with which all of the tape is covered, leaving only the electrode and the copper wire isolation uncovered.