Salt-water Electrolysis gives fluffy brown precipitate?

[rbesfe]

I was demonstrating the electrolysis of salt-water to some of my friends and family, and decided to leave it going to collect some of the gas in tubes in the water. When I returned (about 1.5 hours later) there was a brown, fluffy precipitate and the water had turned a yellowish colour. Anyone have an idea of what this is or a link to a thread with the answer? Thanks!

[Sensei]

Metal electrodes that you used, or wires, dissolved..

Check volume of oxygen produced on positive electrode.

It will tell much about reaction.

 

You need f.e. gold metal electrodes to not produce oxides of metal on positive electrode.

 

The most likely you used iron?

 

Aluminum gives white gel full of bubbles Al(OH)₃ (it can even float on water, when it's full of Hydrogen bubbles).

 

Copper gives first aquamarine/turquoise Cu(OH)₂

after a while it changes to dark color CuO + H₂O (typically couple days)

(once I had container full of nice aquamarine color Cu(OH)₂, and accidentally while moving it hit other container, and within couple minutes it changed to dark color CuO)

 

Iron gives yellow,red,brown color.

 

Lot of salt will also change possible outcome.

Edited October 10, 2014 by Sensei

[Endy0816]

I recently had the same thing with a forgotten Leyden jar. Thought I had something growing in it at first.

[StringJunky]

Table salt has anti-caking agents in it so it could be a by-product of one or more of those..

 

 

An anticaking agent in salt is denoted in the ingredients, for example, as "anti-caking agent (554)", which is sodium aluminosilicate, a man-made product. This product is present in many commercial table salts as well as dried milk, egg mixes, sugar products, and flours. In Europe, sodium ferrocyanide (535) and potassium ferrocyanide (536) are more common anticaking agents in table salt. Natural anticaking agents used in more expensive table salt include calcium carbonate and magnesium carbonate. http://en.wikipedia.org/wiki/Anticaking_agent

[Sensei]

Table salt has anti-caking agents in it so it could be a by-product of one or more of those..

 

 

To check whether contamination is caused by salt you might simply run experiment with the same wires without any salt and leave it running overnight (because it will be going much slower).

Edited October 10, 2014 by Sensei

[Enthalpy]

Salt water electrolysis uses to produce sodium hypochlorite. That would explain the yellowish colour. The odour should tell it.

 

The rest is from the electrodes. Prefer graphite electrodes, for instance from a round battery - beware possible KOH and more in it.

[smhjn17]

A similar thing happened with me ....did u use copper electrodes,if yes then probably its a cu+1 compound which is red brown

[DrDoggy]

A similar thing happened with me ....did u use copper electrodes,if yes then probably its a cu+1 compound which is red brown

or green even

[smhjn17]

Ya...initially cu2+ appears as blue green cu(oh)2 and then gradually yellow green brown oxide of cu1+ forms....the results were quite fascinating

Infact the whole solution gets yellow in a while due to cu2o

[Sensei]

Infact the whole solution gets yellow in a while due to cu2o

 

Cu₂O is insoluble in water.

In fact it's produced on positive electrode in tiny tiny amount, as a layer covering electrode, and then peeling off and instantly sinking to the bottom of container, where it will gather with black CuO.

At first I wanted to show you photo how little you should get Cu₂O, in comparison to CuO.. It's ratio like 1:50+.. In 2 weeks of making CuO using electrolysis I made maybe less than 1 gram of Cu₂O as byproduct.

 

If you didn't buy your Copper metal electrodes by yourself but found somewhere, it might be made of alloy of Copper with something else.

And that secondary metal could be influencing results.

 

Cu₂O looks like:

Edited June 3, 2015 by Sensei

[smhjn17]

For sure this is the color of cu2o but depending upon the size of the lattice...the color can even be yellow or green even( as observed in a benedicts test)...

And the solution turned yellow just due to the suspended particles of cu2o while the electrolysis goes on....

What i observed was that more of yellow cu2o was produced than cu(oh)2 and black cuo was never produced(being in water cu(oh)2 cant dehydrate)

At first even i was surprised and thought that the the electrode is an alloy...but then i tried with pure copper strip ..the results were same

Edited June 3, 2015 by smhjn17

[Sensei]

Please show photos.

 

What voltage U are you using?

 

What is current I while electrolysis?

 

Are you using some salt to make water conductive? If yes, in what amount.
I don't, just tap water, that have enough ions.

 

I have plugged watt meter all the time, and never observed mentioned by you reactions, with just pure water and both Copper electrodes (especially lack of CuO?! Plentiful of Cu₂O?!)

 

Do you have Oxygen coming from positive electrode? I don't have any Oxygen. It all reacts with Copper..

(But I noticed that when there was NaHCO₃ in water, Oxygen was made on Copper positive electrode (in different volume than 2:1 with Hydrogen), but also there was plentiful of other reactions).

 

Did you tried collecting Hydrogen and/or Oxygen from electrodes in containers with scale, like upside down beaker, or upside down graduated cylinder.. ?

To measure volume of gases, their ratio.

While using different metals for electrodes and/or different salts, ratio of produced gases will be varying.

Edited June 4, 2015 by Sensei

[smhjn17]

Arent we talking here about electrolysis of salt water ie nacl with cu electrodes....im not talking abt tap water...my voltage is 9 volts