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topic 4134p2

Why does copper sulphate induce a kind of rust on a nail?

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A discussion started in 1999 but continuing through 2019

June 11, 2013

Q. When an iron nail is kept in copper sulphate solution for about 3-4 hours, which part of nail first gets reacted with the solution?

padma p [last name deleted for privacy by Editor]
student - pondicherry, india

June 17, 2013

Hi Padma. Aren't you supposed to conduct an experiment to get this answer? Don't miss out on the fun parts. Do the experiment, make some observations, tell us what they were, and then we will be very happy to discuss it with you. Thanks.


Ted Mooney, Teds signature
Ted Mooney, P.E. - Pine Beach, New Jersey
Striving to live Aloha

September 17, 2011

Q. I have to do a similar experiment to the people above. In class we slid blue copper sulfate crystal into the bottom of a test tube, added piece of paper and then some water. We then added some sodium chloride, and another piece of paper and more water. Then we took a nail, removed the coating by using steel wool and added the nail. We then again added more water until it covered the nail. We then observed the thing and I'm not sure what really happened. The copper sulfate turned dark purple. The nail had reddish brown substance on it, and I'm guessing that is rust? If it is rust, was that reaction from the salt or copper sulfate?

Allan D [last name deleted for privacy by Editor]
- Bridgeport, Connecticut, USA

September 19, 2011

A. Hi, Allan.

Actually most of the question was answered a few times. But maybe you are younger and unable to understand the answers?

I don't know what you are referring to with the "paper". Maybe you were checking the pH with pH paper?

The copper in copper sulphate is not in copper colored metallic form, but in an ionic form that colors the solution a deep blue. When you put an iron object into that solution, some of the iron from the surface dissolves into the solution, driving out some of the copper from the solution, which is reduced to copper metal on the surface of the iron. That turns the nail copper colored. I'm not exactly sure what is happening to the color of the solution, but some of the blue colored copper is leaving it, and some blackish iron sulphate or iron chloride is going into it.


Ted Mooney, Teds signature
Ted Mooney, P.E. - Pine Beach, New Jersey
Striving to live Aloha

September 20, 2012

Q. Hi. I'm also doing an experiment of breaking up compounds.
So I had to do a lab and I was asked to write the answer for these questions if you can please help to figure it out!
*How is the method of getting Cu out of a CuSo4 solution different from separating the components of a mixture?
*State whether the copper is combined or uncombined (I don't know what to do in this part)
*(a) in the deposit on the nail
*(b) in copper sulfate solution

Perla G. [last name deleted for privacy by Editor]
- New York

September 20, 2012

A. Hi Perla.

When you encounter questions like these, the first thing to ask yourself is: "Have I not yet figured out the answer, or do I not even understand the question?" You used the phrases "breaking up compounds" and "separating the components of a mixture" -- and that should give you some ideas; but you can also google "compounds vs. mixtures". As you study compounds vs. mixtures, the meaning of the word "combined" in this context will hopefully become apparent.

If your teacher actually wrote CuSo4, rather than CuSO4, call him or her out for it :-)
... proper capitalization is crucial in chemistry. Good luck.


Ted Mooney, Teds signature
Ted Mooney, P.E. - Pine Beach, New Jersey
Striving to live Aloha

November 7, 2012

Q. Could you explain why sodium chloride causes iron nails to rust?

ANDERSON [last name deleted for privacy by Editor]
- Pappua, New Guinea

November 9, 2012

A. Hi Anderson. Please explain the experiment that you performed, and the results that you got, which seemed to indicate that sodium chloride causes iron nails to rust, and I will try to explain your findings. Or read the earlier entries on this page. Good luck.


Ted Mooney, Teds signature
Ted Mooney, P.E. - Pine Beach, New Jersey
Striving to live Aloha

March 31, 2013

Q. Why does iron rusts badly if it is placed with copper plate?

Kay A [last name deleted for privacy by Editor]
- bandar seri begawan, Brunei

April 1, 2013

A. Hi Kay. The answer is on this page already. But if you wish to view it from a different perspective, you have two different metals with two different oxidation potentials, connected with both an electrical path and an ionic path, so --

The more noble metal (copper) will steal electrons from the less noble metal (iron) that it is connected to, oxidizing them to positively charged ions which will dissolve into solution. Good luck.


Ted Mooney, Teds signature
Ted Mooney, P.E. - Pine Beach, New Jersey
Striving to live Aloha

March 23, 2015

Q. I am doing an experiment with CuSO4 crystals, then filter paper on top, NaCl, then another layer of filter paper, and iron nail and H20. My question is what does the NaCl do/help in the experiment and what are gas bubbles formed from.

Thank you.

Emily A [last name deleted for privacy by Editor]
- Los Angeles, USA

June 2015

thumbs up signSorry Emily, it's too vague for me. I don't know what gas bubbles you are speaking of, nor why your procedure puts NaCl between the CuSO4 and the iron nail, or what you procedure really looks like. As a student it's important for you to distinguish between questions to which you don't know the answer vs. questions where you don't even understand the question. In the former case you are right to seek the answer, but in the latter case you must get clarity from your teacher ... and I'm not quite sure which is the case here. Good luck.


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Ted Mooney, P.E. RET - Pine Beach, New Jersey
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June 7, 2015

Q. What confuses me is why the reaction is a displacement reaction and not double displacement reaction like that of Sodium Sulphate and Barium Chloride? Like copper is being displaced from its sulphate, so is Fe from the nail. Why doesn't the iron erode from the nail up to the point where all Cu^2+ ions have been replaced by iron and Cu2 forms a sediment/precipitate?

Srishti G [last name deleted for privacy by Editor]
- Delhi, India

June 2015

A. Hi Srishti. A double displacement reaction is of the form
AB + CD => AD + CB

Your reaction of
CuSO4 + Fe => Cu + FeSO4 is of the form
AB + C => A + CB and there is only one displacement.

One reason the reaction doesn't continue until all Cu^2 ions have been replaced is that the iron becomes completely covered with copper in metallic form and there is no more iron exposed, so CuSO4 can't reach the iron anymore. A second issue to consider is that ferrous sulphate is rather soluble in water, so it doesn't tend to precipitate in this situation. Good luck.


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Ted Mooney, P.E. RET - Pine Beach, New Jersey
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Will Nickel/Cobalt sulphate deposit onto a Bare Steel Rod (Iron) like Copper sulphate does

October 10, 2015

Q. Fe + NiSo4 = Ni + FeSo4, will the resulting elemental Nickel or Cobalt plate over an iron rod? I have done this type of immersion plating using a simple iron nail and Copper sulfate, so I was wondering if the same could be applied with nickel sulfate or cobalt sulfate?


Marvin S [last name deleted for privacy by Editor]
hobbyist - Nicaragua

October 2015

A. Hi Marvin. Please google "galvanic series chart" and "seawater series chart" and you will find that pure nickel is even more noble than copper, so it looks like it should deposit on the iron nail even more readily ... but I'm quite sure that you'll discover that in fact it doesn't "immersion deposit" on iron anyway. One thing that makes science fun is that it's not dead easy and completely predictable by the simplest of rules; rather, it's always complicated enough to challenge us.

So please try it and tell us what happens ... then we can attempt to figure out why. Good luck


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Ted Mooney, P.E. RET - Pine Beach, New Jersey
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October 15, 2015

A. Marvin,
I believe what you are asking for is the "electroless nickel" plating process that was first developed sometime around the 1950s.

sidebar2 ----------
You may be reading that chart wrong. My lists of standard reduction potentials for half cell reactions shows the reduction of Cu(II) to Cu(0) to have a positive value (trending towards a spontaneous reaction) while the reduction of Ni(II) to Ni(0) has a negative value (trending towards a non-spontaneous reaction). However, the reduction of Fe(II) to Fe(0) has an even more negative value, which means the oxidation (reverse reaction, positive value) ought to be strong enough (but only just barely) to still drive the nickel reduction forward under ideal conditions. Clearly most plating tanks are not ideal conditions, which is why the EN process relies on the presence of an additional reducing agent.

ray kremer
Ray Kremer
Stellar Solutions, Inc.
supporting advertiser
McHenry, Illinois
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thumbs up sign Thanks Ray, I may have misread, or may be misunderstanding something -- everyone always needs more schooling, and I appreciate when people make me realize I don't understand something I thought I did :-)

Although your 'trending towards' is correct, it's not quite the case that positive values mean spontaneous reduction to metal and negative value indicate spontaneous oxidation to ions. The zero point or reference point for half cell reaction 'voltages' is hydrogen and standard conditions; not ionization-reduction go/no-go.

Autocatalytic reactions (electroless nickel) are a quite different thing from immersion/displacement reactions (copper sulphate on steel) though. Iron doesn't dissolve into solution in an electroless nickel tank and the reaction doesn't stop when the iron is completely covered: the reaction is only Ni++ => Ni0; there is no corresponding Fe0 => Fe++ involved. The electroless nickel reduction reaction is 'spring loaded' by hypophosphite primed to reduce nickel ions to nickel metal.


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Ted Mooney, P.E. RET - Pine Beach, New Jersey
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September 8, 2018

Q. Hello! I'm currently in 10th grade and we have a lab experiment about placing steel wool into 10% solution of CuSO4. We placed it inside a sealed test tube and heated it for over 2 minutes. The steel wool became duller in terms of shine after heating it up. I searched up in a couple of websites that it had a displacement reaction (single if I'm correct) but I was hoping for a more in depth explanation as to why it became duller and what was happening and what the elements were "doing" to each other. I'd really appreciate a quick response, thank you!

Pristine A [last name deleted for privacy by Editor]
- Pasig, NCR, Philippines

September 2018

A. Hi Pristine. Yes, it's a single displacement reaction, iron displacing copper:
Fe + CuSO4 => Cu + FeSO4

Assuming the intended reaction actually occurred, the 'dullness' is due to the fact that you formerly saw iron on the surface of the steel wool, but after this reaction you are now seeing copper, because the surface of the steel wool is now covered with copper.


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Ted Mooney, P.E. RET - Pine Beach, New Jersey
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April 23, 2019

Q. I'm in 9th Grade and we did copper (II) sulfate and steel wool. The steel wool changed color. Is it a chemical change? If it is, what are other factors that helps determine that it is a chemical reaction?

Red Dacup
- Mindanao, Philippines

May 2019

A. Hi Red. Your problem is probably not that you don't know the answer, but that you don't really understand the question :-)

You had a lesson, or perhaps a reading assignment, about the difference between a 'physical change' and a 'chemical change'. So google 'physical change vs. chemical change'.

A 'physical change' is one which changes the physical properties of the substance but is relatively easily reversed, such as: you can change liquid water to solid ice by cooling it, and restore it to liquid again by heating it. You can change liquid water to gaseous steam by heating it, and you can collect the steam and let it condense back to liquid.

A 'chemical change' involves making and breaking chemical bonds; it is usually quite difficult to reverse; and it generally either releases energy (such as when something burns and gives off heat) or (less commonly) absorbs energy. Although you witnessed a change in a physical property -- some of the blue copper in the solution became orange copper on the steel wool -- you can ask yourself two questions: 1. How would you go about reversing the process and getting the orange metal off of the steel wool and back into solution? It doesn't sound easy and straightforward to me. 2. Why did this color change occur? I'm not sure how far you've gotten in chemistry and if you know what reaction actually occurred. But the orange copper is copper metal whereas the blue copper is copper combined with other atoms, which means chemical bonds were made or broken.

The process gives off or absorbs heat if it is a chemical reaction, but it is probably beyond 9th grade level to design an experiment to measure a small heat change in a system like this one, so you probably need to forego that test of physical vs chemical changes. Good luck.


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Ted Mooney, P.E. RET - Pine Beach, New Jersey
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sidebar2 September 26, 2019

Q. Will copper sulfate protect steel for exterior use. I like the color of the treated metal, but I need corrosion protection as the items will be in mud, water, etc. Also, will it have any negative effect on the strength of steel springs?

Daniel Sanford
- Northport, Alabama

October 2019

A. Hi Daniel. An immersion deposit of copper on steel from a copper sulphate solution isn't useful for much, including corrosion resistance unfortunately. Even actual copper electroplating, which is much thicker and more adherent is unlikely to be useful for corrosion protection in mud and water. And yes, unless precautions are taken, including careful and timely baking for hydrogen embrittlement relief, it will weaken the springs. Sorry :-(


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Ted Mooney, P.E. RET - Pine Beach, New Jersey
Aloha -- an idea worth spreading

October 2, 2019

thumbs up sign Thanks so much for the response. This was very helpful.

Daniel Sanford [returning]
- Northport, Alabama

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