Martian rust

Iron nail turns red in a solution of copper salt

Scientific name: The nail becomes red because it is covered with a thin layer of copper. Copper settles on the surface of the nail because it is a less active metal than iron.


Martian rust - An iron nail turns red in a solution of copper salt

by MEL Science

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Copper - Iron Single Replacement (720p Time-Lapse)

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Wear protective gloves

Always follow general safety recommendations. Please note that conducting chemistry experiments you must comply with the relevant legal procedures in your country.

Perform this experiment

Reaction formula

CuSO4 + Fe → FeSO3 + Cu

Step-by-step instruction

  1. Pour 0.5M CuSO4 solution into a small beaker.
  2. Take an iron nail. Attention! The experiment is not possible with a steel nail.
  3. Put the nail into the beaker with the CuSO4 solution.
  4. Wait 10 seconds.
  5. Remove the nail - its surface is covered with a thin layer of red copper.
  6. If the nail is placed back into the CuSO4 solution for 15 minutes, the nail will be covered with a thick uneven layer of spongy copper.
  7. If an iron nail is placed in the CuSO4 solution briefly (about 10 seconds), it will be covered with a thin layer of red copper. If left in the solution for a longer time, the nail is covered with loose copper build-up.

Scientific background

Why does the nail become red?

The nail becomes red because it is covered with a thin layer of copper. Iron from the surface of the nail goes into solution and the copper from the solution forms a thin layer on the nail surface. The copper in the solution is in the form of a positively charged ion Cu2+. This means that the copper is missing two electrons. Each electron carries a negative charge. To turn into a metal (uncharged) form Cu0, copper takes the missing electrons from iron and turns into metal.

Why does copper settle on the surface of the nail?

Copper settles on the surface of the nail because it is a less active metal than iron. The activity of a metal is its ability to donate electrons, becoming a positively charged ion. The more active the metal is, the more it tends to become an ion. In this case, the iron in the nail tends to become an ion and gives up its electrons to copper in the solution. Copper accepts electrons from the solution and turns into metal form.

Why is iron more active than copper?

In order to introduce a measure of metal activity, chemists came up with a special term called reduction potential. Without going into the details of the calculation and measurement of reduction potential, you can simply put metals in a series in order of decrease in its value. Metals with the highest redox potential more easily act as reducing agents and readily donate electrons. These metals are located at the top:

K (potassium)

Ca (calcium)

Li (lithium)

Na (sodium)

Mg (magnesium)

They have just one or two electron and it is easy to part with them.

The greediest are precious metals. If we use an analogy from the real world, we can say that poor people spend money more easily, and the rich are often very thrifty to trivial matters. So it is possible to remember that noble metals are not inclined to give up their "treasure" - electrons. Therefore, at the end of the activity series there will be the following metals:

Cu (copper)

Hg (mercury)

Ag (silver)

Au (gold)

Iron on the other hand occupies an intermediate position between the highly active metals and precious metals. Therefore, if copper and iron were to "fight" for an electron, iron, having greater activity, gives the electron to copper. The main reason for this is the larger reduction potential of iron. Reduction potential is an experimentally measured value, and this value is more for iron than for precious metals. But you can remember the three main groups of metal activity: the elements of the first and second groups (columns of the periodic table) are the most active. Precious metals are least active. Other metals occupy an intermediate position.


Published on 10 January 2016

  • Fire
  • Heating with fire
  • Explosion
  • Poisoned gas
  • Organic
  • Electricity
  • Solution
  • Oxidation reduction
  • Color change
  • Precipitate
  • Gassing
  • Catalyst