Amazing iron

Study the chain of iron chemical transformations

Difficulty:
Danger:
Duration:
20 minutes
Experiment's video preview

Reagents

Safety

  • Put on protective gloves and eyewear.
  • Conduct the experiment on the plastic tray.
General safety rules
  • Do not allow chemicals to come into contact with the eyes or mouth.
  • Keep young children, animals and those not wearing eye protection away from the experimental area.
  • Store this experimental set out of reach of children under 12 years of age.
  • Clean all equipment after use.
  • Make sure that all containers are fully closed and properly stored after use.
  • Ensure that all empty containers are disposed of properly.
  • Do not use any equipment which has not been supplied with the set or recommended in the instructions for use.
  • Do not replace foodstuffs in original container. Dispose of immediately.
General first aid information
  • In case of eye contact: Wash out eye with plenty of water, holding eye open if necessary. Seek immediate medical advice.
  • If swallowed: Wash out mouth with water, drink some fresh water. Do not induce vomiting. Seek immediate medical advice.
  • In case of inhalation: Remove person to fresh air.
  • In case of skin contact and burns: Wash affected area with plenty of water for at least 10 minutes.
  • In case of doubt, seek medical advice without delay. Take the chemical and its container with you.
  • In case of injury always seek medical advice.
Advice for supervising adults
  • The incorrect use of chemicals can cause injury and damage to health. Only carry out those experiments which are listed in the instructions.
  • This experimental set is for use only by children over 12 years.
  • Because children’s abilities vary so much, even within age groups, supervising adults should exercise discretion as to which experiments are suitable and safe for them. The instructions should enable supervisors to assess any experiment to establish its suitability for a particular child.
  • The supervising adult should discuss the warnings and safety information with the child or children before commencing the experiments. Particular attention should be paid to the safe handling of acids, alkalis and flammable liquids.
  • The area surrounding the experiment should be kept clear of any obstructions and away from the storage of food. It should be well lit and ventilated and close to a water supply. A solid table with a heat resistant top should be provided
  • Substances in non-reclosable packaging should be used up (completely) during the course of one experiment, i.e. after opening the package.

FAQ and troubleshooting

I apply a magnet to the cup, but nothing happens. What to do?

Perhaps, you are using a very weak magnet. For instance, some souvenir magnets that hold just fine on a fridge may not be suitable for this experiment. Try finding a stronger magnet.

Step-by-step instructions

Iron reacts with citric acid, creating ferrous citrate FeC6H6O7.

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The unreacted iron can be collected with a magnet.

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While the magnet is holding the residual metallic iron, you can pour out the colorless ferrous citrate solution.

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Hydrogen peroxide H2O2 oxidizes iron(II) to iron(III), forming a yellow ferric citrate FeC6H5O7 solution.

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Potassium hexacyanoferrate(II) K4[Fe(CN)6] reacts with iron(III) ions, yielding prussian blue, which is insoluble.

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To repeat the experiment, wash the Petri dish.

Disposal

Dispose of solid waste together with household garbage. Pour solutions down the sink. Wash with an excess of water.

Scientific description

What happens when we add citric acid to iron powder?

When citric acid is added to iron powder, a whole chain of reactions initiates. First, citric acid reacts with metallic iron Fe. Being a typical metal, iron readily donates electrons and becomes “oxidized”. Simultaneously, the protons H+ in citric acid become reduced producing hydrogen H2 in form of gas bubbles. We observed the gas bubbles in the experiment. This process is represented by the following electrochemical reaction:

2H+ + 2e → H2

As the solid iron Fe donates its electrons to the hydrogen ions, it evolves into its oxidized form and turns into Fe2+ ions. Here is the corresponding reaction:

Fe – 2e → Fe2+

Let’s summarize the entire equation:

Fe + C6H8O7 → FeC6H6O7 + H2

These reactions are called redox reactions, or reduction-oxidation reactions. They always involve two components: an oxidizer that accepts electrons and a reducer that donates them.

What happens when we place a magnet under the bottom of the beaker?

Iron filings are attracted to the magnet, which we hold on the outside of the bottom of the beaker. The filings turn into fancy needles: the closer to the center of the magnet, the sharper and taller the needles. Such an arrangement isn’t by chance: the filings are arranged around the magnet along certain axes.

This magnetization occurs due to the specific structure of the iron atom.

Learn more

Only three elements, because of their unique structure, can be permanent magnets: namely, iron, nickel, and cobalt. Their atoms contain charged particles – electrons. The electrons rotate around a nucleus in the same direction and, thus, create a magnetic field. Substances, which create magnetic fields, are called ferromagnetic

Each magnet has two poles (north and south), which are always found on opposite ends. The force of the field is directed from the north pole towards the south pole. Although a human eye can’t see a magnetic field, this experiment demonstrates what it “looks” like.

Why did the solution change its color as we added hydrogen peroxide and potassium hexacyanoferrate?

During the last stage of our experiment, we witnessed two reactions simultaneously. Let’s examine them separately.

The first reaction is that of ferrous iron and hydrogen peroxide H2O2 commonly used as an antiseptic medicine. Upon reaction with H2O2, the Fe2+ ions are oxidized and form Fe3+ ions. However, the Fe3+ ions remain bound to the citrate ions, and it is this complex that produces the deep yellow color of the solution. Simultaneously, as the hydrogen peroxide is reduced, its molecules are transformed into water molecules.

The second reaction takes place between our mixture and that of potassium hexacyanoferrate K4[Fe(CN)6]. When potassium hexacyanoferrate is added to the solution, it turns bright blue at the place where drops are deposited. This beautiful color is due to very fine granules of so-called Prussian blue. Prussian blue is a water-insoluble pigment with a complex formula based on KFe[Fe(CN)6]. The last, but nonetheless quite important, participant of this reaction is the oxygen from the ambient air.

The formation of Prussian blue occurs even when there is only a tiny number of iron ions in the solution. As a result, this reaction is used in qualitative tests to determine Fe2+ ions.