Nails in Copper (II) Chloride

[Derrell]

hi, im new here and can anyone of you tell me why nails react the way it does when it interacts with copper (II) chloride?

 

thanks

[jowrose]

When you place a steel (iron) nail in a CuCl2 solution, the iron first displaces the copper and forms FeCl2, because iron is more reactive than copper (take a look at an activity series of metals). If you leave the FeCl2 out (it is a clear solution, with a slightly green tint) in contact with air, it slowly oxidizes to form FeCl3 (a yellow-orange solution). Of course, the colors could be mixed up, as no nail is pure iron. You will get impurities ranging from carbon (if it's a steel nail) to magnesium to nickel.

 

If I'm wrong, I hope somebody will correct me...

[rakuenso]

i thought you meant finger nails for a second

[Derrell]

thanks jowrose!

[Ferdinand]

Interestingly, I carry out a demo of iron nail in copper II sulphate solution regularly, or get my students to do it themselves. As expected, bright "salmon-pink" solid appears on the nail as the redox process occurs.

 

However, why does the redox process between iron nail's atoms and copper II ions in copper II nitrate solution NOT occur? That is, the iron nail remains shiny. Please excuse my ignorance, but no-one has been able to explain this anomaly to me.

[woelen]

This sounds interesting. If I understand well from your post, you did the same experiment twice under the same conditions, once with copper nitrate and once with copper sulfate?

 

I have both copper nitrate and copper sulfate and I'll see if I can repeat the experiment. Could you provide me with precise information about what you did?

[Ferdinand]

Okay over the years(about 15-20) I have quickly set up the metal displacement demo of a large shiny iron nail in royal blue copper sulfate solution.If not, I've gotten my students to do it. Each time as expected, the predicted observations are made - salmon pink solid produced, blue colour fades. Sometimes, I have unwittingly used copper nitrate solution instead or copper sulfate solution - thinking that all I really required was a ource of copper II ions in solution. But every time I've dipped that shiny iron nail into the copper II nitrate solution (and left it there) the iron nail remained shiny. No redox process. It has gotten to the stage where I make sure that it is NOT a copper nitrate solution to get my salmon pink solid.

[woelen]

It is clear to me now what you did. I'll repeat the process. I have very pure Cu(NO3)2.3H2O and CuSO4.5H2O and I'll use that for the experiment. For the nail I'll use an ordinary iron and shiny nail.

 

I also have CuCl2.2H2O and for each of the three copper salts I intend to do the experiment. The results will be posted here as soon as I have results.

[YT2095]

just a thought, but isn`t copper chloride the end result of Iron Chloride PCB etchant when it`s exhausted?

 

the iron displaces the copper until the reactions complete, so adding iron back into won`t reverse it or even react?

[woelen]

When you immerse a PCB in a solution of FeCl3, then you'll get some complex mix of copper (I) and copper (II) ions. Indeed, with an iron immersed in copper (II) chloride solution, I do not expect formation of a copper layer on the iron, but I still expect it to react. I expect formation of iron (II) or even iron (III), and formation of copper (I) species. Probably the liquid will becomes very dark brown, due to formation of mixed-valency complexes.

 

I think Ferdinand's experiment is interesting to do and see the effect of the anion on the total mix. I'll perform the experiment tonight or tomorrow and I'm really curious what will happen. I expect differences with all three different salts. I'll try to give an explanation, as soon as I have experimental results.

[YT2095]

I`ll give the Nitrate one a try now, I don`t have any copper chloride, and the sulphate one`s perfectly established as a working procedure.

it`ll be interesting to compare results

 

edit: Ouch! it`s a good thing I decided to try this for myself when I did, most all of my copper nitrate has turned to liquid and some`s leaked out (no damage done), that was lucky!

 

edit2: there`s no observable reaction taken place, I`ve even examined the iron under a microscope for copper particles, Nothing, not even the tiny rusty bits seem affected. I`ll point out as a sidenote though, Copper Nitrate will stain your hands if not washed off right away

[YT2095]

Wow! you`re not going to beleive this, but where I cut the nail in half there is Copper plating! and it`s moved up about 1.5mm, the rest is still unchanged albeit a little darker in color and the little rust patches are still the same. there`s also a white(ish) ppt at the bottom of the tube, but that MAY be unrelated as my copper nitrate had liquified almost entirely and the inside cap of the bottle was a waxed cardboard (that`s now a blue/green color).

[woelen]

I've done the three experiments with copper sulfate, copper (II) chloride and copper nitrate. The effect for each of the three salts is very different.

 

First I did experiments with different types of nails, but these results are very inconsistent. Some nails are copper plated quickly, also in nitrate solution, other nails are not copper-plated. Apparently these nails have different composition, so Ferdinand's observation's cannot reliably reproduced with the nails, I have in my barn.

 

===============================================

 

So, I took coarse powdered 99.9% iron (lab grade powder, not the cheap filings or powder used for magnetism experiments). With this iron powder I obtained very interesting results.

 

Copper sulfate solution: The iron grains are copper plated fairly quickly. Within a few tens of seconds, the color of the grains shifts from grey to red/salmon. The liquid remains blue. After 4 hours, the liquid has become a little turbid and brown/yellow. This looks like hydrolysed iron (III).

The observations can nicely be explained:

metal displacement: Fe + Cu(2+) --> Fe(2+) + Cu

The Fe(2+) lateron is slowly oxidized by oxygen from the air, forming basic Fe(3+) compounds.

 

Copper nitrate solution: Even after 4 hours, the liquid still is nice bright blue and clear. The iron still is grey. It has become slightly darker grey, but there definitely is no copper plating. So, here I perfectly reproduce Ferdinand's observation, now with lab grade chemicals.

This observation puzzles me indeed. I'll look more into this and come back on this later with variations (e.g. pH and concentration).

 

Copper (II) chloride: This is most remarkable. Within 10 seconds, all iron is displaced by copper. A coarse grainy red/brown precipitate is formed and the liquid becomes very light green (color of iron (II) chloride in solution). After shaking for a minute, the liquid turns brown/yellow and turbid. This indicates oxidation of the iron (II), and formation of basic iron (III) compounds, which indeed are brown/yellow. See my webpage on iron (III) species and their hydrolysis.

Next, I checked what the brown/red precipitate is. I rinsed it two times with clean water and then added 10% HCl. The precipitate does not dissolve. This means that it is copper metal. If it were Cu2O, then it would dissolve quickly in the dilute HCl.

The observations with copper (II) chloride can also be understood very well. The complex CuCl4(2-), present in this solution is a fairly strong oxidizer, which is capable of oxidizing Fe to Fe(2+), itself being reduced to copper metal and free Cl(-) ions:

Fe + CuCl4(2-) --> Fe(2+) + Cu + 4Cl(-)

The Fe(2+) in turn is oxidized by oxygen from the air.

This experiment also shows that CuCl2 does not oxidize the iron to Fe(3+). As YT already mentioned, that would not be the expected thing, because FeCl3 is used as PCB etchant, which dissolves copper. So, with Fe(3+), copper metal is oxidized to copper ions, and the Fe(3+) is converted to Fe(2+). With Fe and copper ions, however, the copper ions are converted to metal and the Fe is converted to Fe(2+).

[YT2095]

well I`ve left my nail in overnight, now the soln is very green and there`s copper particles at the base of the test tube, it certain has reacted here albeit very slowly.

Woelen, you seem to be sugesting that it`s impurities in the nail I`ve used, and although I agree that there certainly will be some as it`s Steel rather than iron, what impurity would be the most likely to show a positive result?

the Carbon and Silicon content wouldn`t be reactive.

[woelen]

The nails I use probably contain quite some zinc. This often is used to make them less susceptible to rusting, but a zinc nail (or one, containing quite some zinc) will be copper plated in any solution, containing copper (II) ions, even in copper nitrate solution.

 

The metals zinc, cadmium, magnesium and aluminium most likely will cause the formation of copper, regardless of the anion.

 

I also did another experiment with another nail. This gives a dark green/black solution when Cu(NO3)2 is used and it becomes lightly copper-plated in a solution of CuSO4. So, using nails is indeed very inconsistent. The problem is that we do not know the impurities. This apparently also differs from country to country.

 

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To me it is a real surprise to see, that the anion has such a strong influence on the displacement reaction between iron and copper. The effect of chloride I already got aquainted with, I've seen that before many times, but the effect of the nitrate really puzzles me. As you see, the highschool text books oversimplify things. Even with seemingly simple things like displacement reactions there is a lot more to tell about this than what the school books suggest. I'll certainly dive into this more deeply.

[woelen]

Sorry for the double post, I cannot edit my previous post anymore.

 

I also did an experiment with slightly acidified solution of Cu(NO3)2. The solution was acidified with a few drops of dilute (2 mol/l) HNO3. These little drops of acid result in almost immediate copper plating of the iron particles and the liquid becomes dark green.

 

Apparently, slight acidification of the nitrate solution makes the copper-plating much faster. The green color also can be explained. HNO3 is reduced by iron and/or copper metal, which is converted to NO and/or NO2. This in turn results in formation of the deep brown [Fe(NO)(H2O)5](+) complex. What remains puzzling, however, is that neutral copper nitrate does not result in copper plating.

[YT2095]

Hmmm... there`s No annomaly then with my result either!

as when I took the top off my container there was a VERY strong smell of Nitric acid (NO2), so in all probability, mine had decomposed somewhat and become a little acidic (hence the smell).

 

many hours on and the experiment is Still in the test tube, there is a tiny amount of rusty bubbles on the surface now, however this MAY BE due to the fact that I take the iron out by sliding a magnet up the side of the tube and perhaps some got oxidesed whilst out, and subsequently ran back down again after?

[woelen]

YT, is your Cu(NO3)2.3H2O a commercial sample or did you make it yourself? Home-made copper nitrate is very hard to make free of nitric acid. I once made nickel nitrate and even after I obtained it as a solid, thin fumes could be observed above the solid.

 

Another thing is that copper nitrate is very deliquescent. I have heard of more people that their copper nitrate had liquefied after a year of storage. I purchased 100 gram of this stuff two years ago in a drugstore and it still is nice dry and crystalline. I put it in a container with a screw cap. This container is put in a plastic bag, which is tightly closed. This plastic bag with the container inside is put in a larger outside container with screw cap again. The plastic bag inside is essential. It prevents fresh (and humid) air to cycle in and out of the container on varying air pressure and temperature.

[Ferdinand]

I have found this dialogue most enlightening...another reson why I'm so glad I've found this forum.

 

Interestingly, copper II sulfate solutions are slightly acidic, of course. Copper II nitrate solutions should also be slightly acidic due to aquated copper ions undergoing some hydrolysis - as in sulphate solutions. So, I am still totally ignorant of the lack of displacement, but jumping with excitement at Woelen's and YT's inputs. Thank you for taking this one up. Your investigative dialogues are so full of integrity that I seek to use the transcripts in my chem classes when we cover redox & metal displacement - with your permissions??

[woelen]

Of course you have my permission . I think it is good to show to the pupils that seemingly simple things in chemistry are not always that simple. When I myself was in high school (more than 20 years ago), I though that the information in schoolbooks was an accurate description of reality. Lateron I learnt that this only is a strongly simplified approximation.

[YT2095]

sure you can use them, afterall it`s only scientific findings we`ve presented

talking of which, day 2, and the soln is now a very light green with hints of orange rust and there are clearly noticable bubbles at the liquid surface now.

the diameter of the nail is almost double with a spongey mass the bottom half is quite clearly copper metal and as this progresses up the nail towards the top the color is a dark brown.

where I`ve been sliding the metal up the tube to look at it in air, it left a few droplets of this liquid which has now turned almost black with a shiney colored surface a bit like oil-on-water effect.

I`ll leave it for another day, and then take it out, wash it up and compare it to the other half of the nail I cut it from.

 

edit: Woelen it was "home made" copper nitrate, basicly 35amp copper wire dissolved in 70% nitric acid, copper in excess, then allowed to crystalise over gentle heat, and then the copper removed. I think in future I`ll store this as a liquid as I do with my Silver nitrate, it`ll save alot of storage hassle

[jdurg]

A short while back we were discussing acids and acid strength and it was rightfully mentioned that while nitric acid is considered a strong acid, it really doesn't dissociate 100% and is the 'weakest' of the 'strong' acids. Is it possible that the NO3- ions are pulling away some hydrogen ions from water to form the HNO3 molecule which leaves a miniscule amount of free OH- ions in solution? The OH- ions could be passivating the surface of the iron nail and thus not allowing it to react. If the amount is small enough, then any copper hydroxide that forms would remain in solution due to the very tiny bit present. This would also explain why an acidified nitrate solution will cause the reaction to occur because the extra H+ ions remove this passivated surface from the iron nail. hmmm......

[woelen]

No, I cannot agree with this explanation, because then with CuSO4 this effect would even be stronger.

 

The sulfate ion is derived from the acid ion HSO4(-), bisulfate, which is much weaker than nitric acid. If Cu(HSO4)2 would result in copper-plating and CuSO4 would not, then I could agree, but CuSO4 does do the copper plating very well.

 

I myself am thinking in the direction of oxidative passivation of iron. It is known that iron (and also many other metals like magnesium and aluminium) can be made more corrosion resistant, when treated with an oxidizing solution (e.g. potassium dichromate or dilute HNO3).

 

This effect is used for making nails less susceptible to corrosion and it also is used in pyrotechnics, to make magnesium-containing compositions more stable on storage. For this purpose, the metal is treated with K2Cr2O7 for a while and then cleaned again and then used. It might be that the nitrate from the Cu(NO3)2 has something to do with this, but I only heard the bells ringing, I have no sound explanation for this.

[Ferdinand]

Woelen,

 

an interesting response from Ann....March 1, 2006

 

An aqueous solution of copper(II) sulphate will contain the hexaaqua ion and the pentaaquamonohydroxyl ion, one of which is violet and one green (Having been retired many years, I've forgotten which is which, but the answer was contained in Dr. Alan Sharpe's Inorganic Chemistry, published many years ago. It may be included in one of his later textbooks.) Is it possible that the violet ion changes to the green ion under the conditions discussed? The commonly encountered blue solution contains a mixture of the two ions.

 

Ann Burton

- Macclesfield, Cheshire, UK

[woelen]

Wow, this sounds really interesting! I've never heard of this before. How did they discover this? Is it possible to have only one of the ions in solution? If I make the solution very acidic, then still the liquid is blue, and not green or violet. Wouldn't the ion [ce]Cu(H2O)5(OH)^{+}[/ce] be totally converted to [ce]Cu(H2O)6^{2+}[/ce] in non-coordinating strongly acidic solution. I've done this experiment with HNO3 and H2SO4, but with both the solution remains as blue as without the acid. With HCl, the solution turns green, but that is due to formation of the complex ion [ce]CuCl4^{2-}[/ce].