Why Does Baking Soda + Vinegar + Toilet Paper Turn Blue?

[RestlessMind]

So, a long time when I was little and fiddling with the ol baking soda - vinegar reaction, I had placed some baking soda, toilet paper, and vinegar into one bowl/dish and let it react and get the toilet paper all wet. Then (for an unknown reason) I electrocuted it with a 9V battery, sticking two leads into the wet paper separated by a thin section of the paper. The water (with a dilute of sodium acetate according to the results of the reaction) sizzles a bit and then the paper turns blue. Darker blue the longer I hold the leads there.

So, my question is, why does it turn blue?

 

[Borek]

Probably some dye on the paper, perhaps changing color because of pH changes, but no idea about details.

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[RestlessMind]

I'll try just the paper with the water, and then we'll know if the sodium acetate solution has anything to do with it.

 

[RestlessMind]

Same effect with simply wet tissue. Also, I noticed that the positively charged electrode seems to oxidize extremely rapidly and no longer conducts electricity after that (obviously).

 

[Borek]

Try with electrodes made of different material.

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[chemisttree]

Copper leads anyone?

 

[RestlessMind]

They only seem to be made of copper on the inside, whereas on the outside there is a silver-colored metal. I don't know what it is.

What about the color change?

 

[Borek]

We are aiming at the fact that anode can get oxidized to blue Cu²⁺. That's why I asked about using other electrodes - if they will be not made of copper and there will be no blue color, we will know what was going on.

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[RestlessMind]

Ah! I'll see if I can find some and report back when I've repeated the experiment with them.

 

[chemisttree]

Nickel acetate or bicarbonate?

 

[RestlessMind]

What?

 

[Borek]

Other potentially bluish compounds that can appear if your wires are nickel covered.

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[RestlessMind]

I would say that's right, but I am pretty sure that Nickel is ferromagnetic, but these wires don't seem to be attracted to a magnet.

 

[Borek]

It doesn't have to be pure nickel, more like some alloy. And coating can be so thin you won't see any effect.

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[RestlessMind]

Ah, well then it is probably nickel. I don't know if there is any way to be sure, though.

So, nickel acetate or bicarbonate? Why is that forming with the process I am doing?

 

[Borek]

Something is getting oxidised on the electrode - that's effect of charge crossing phase boundary (solid/liquid). It is either nickel or copper. Cations need presence of some counterion - acetate is being present as you started with acetic acid, carbonate is present as carbon dioxide is always present in atmosphere.

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[RestlessMind]

And they're both blue. So is there anything more accessible than a mass spectrometer that'll tell us what the blue stuff is, or are we to settle with that it might be either of those two compounds? :P

 

[Borek]

It can be also a mixture.

A drop of dimethylglyoxime solution put on the spot should give pink color if it is nickel. There must be many other ways to skin that cat, but that's the only one I can think of right now.

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[RestlessMind]

dimethylglyoxime

what?

 

[Borek]

It is just a reagent.

http://en.wikipedia.org/wiki/Dimethylglyoxime

Much cheaper than mass spectrometer

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[RestlessMind]

Sounds good. :P

 

[chemisttree]

../carbonate is present as carbon dioxide is always present in atmosphere.

I was thinking of the baking soda as well.

 

[Borek]

Honestly - I forgot what was the original setup

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