Fe34 is a mixed valence oxide of iron which have some basic property ví it can react with HCl. Let us see what happens when both are reacted.

Fe3O4 iron is present in the +2 and +3 oxidation states due to tát the +2 oxidation state which is the basic property and for this reason, it can react with HCl. The reaction does not require any kind of catalyst or other parameters lượt thích temperature and pressure.

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Let us discuss the mechanism of the reaction between HCl and Fe3O4, the reaction enthalpy, the type of reaction, product formation, etc in the following part of the article.

1. What is the product of HCl and Fe3O4?

Ferric chloride and ferrous chloride are formed as major product along with water molecule when HCl and mixed Fe3O4 are subject to tát reaction, due to tát the different oxidation states of iron.

Product of the HCl and Fe3O4

2. What type of reaction is HCl + Fe3O4?

The reaction between HCl and mixed valence oxide of iron is a redox reaction where chlorine atoms are oxidized and iron gets reduced. Also, it is one kind of acid-base reaction along with a precipitation reaction because the product is precipitated.

3. How to tát balance HCl + Fe3O4?

HCl + Fe3O4 = FeCl2 + FeCl3 + H2O this reaction is not balanced yet because the atoms are not equal for the left side and right side, ví we have to tát balance the equation in the following way,

  • Step 1 – We first labeled all the reactants and products by A, B, C, D, and E as coefficients because there are five molecules present.
  • The reaction will look lượt thích this,
  • A HCl + B Fe3O4 = C FeCl2 + D FeCl3 + E H2O
  • Step 2 –   Now we use the equation by the suitable number, the coefficient already labeled as alphabet reactants and products.
  • Fe = 3B = C + D, Cl = A = 2C + 2 chiều, O = 4B = E, H = A = 2E
  • Step 3 – Now using Gaussian elimination we calculate the value of each coefficient and variable,
  • A = 8, B = 1, C = 1, D = 2, and E = 4
  • So, the overall balanced equation for the above reaction is,
  • Fe3O4 + 8HCl = FeCl2 + 2FeCl3 + 4H2O

4. HCl + Fe3O4 titration

Fe3O4 can be titrated against HCl under a suitable indicator to tát estimate the amount of iron in a given sample of Fe3O4, it can be done in some processes,

Apparatus used

A burette, conical flask, burette holder, volumetric flask, and beakers are required for titration.

Titre and titrant

Here HCl served as titrant which is taken in the burette and Fe3O4 will be the molecule to tát be analyzed.


The titration of HCl and Fe3O4 is done in acidic pH. Phenolphthalein is the perfect indicator which is pink in a basic medium and colorless in an acidic medium.


The burette is filled with standardized HCl and Fe3O4 is taken in a conical flask and mixed with an indicator. Then titration is started by adding HCl from the burette in a conical flask dropwise. After some time when the endpoint is reached indicator shows a color change which indicates that the titration is completed.

We repeat the titration several times for better results and then we estimate the iron quantity by the formula V1S1 = V2S2.

5. HCl+ Fe3O4 net ionic equation

The net ionic equation for the HCl is proton along with chloride and for the product, ferrous and ferric chloride along with chloride, proton and hydroxide ions come from water.

H+ + Cl + Fe3O4 = Fe2+ + 2Cl + Fe3+ + 3Cl + H+ + OH

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6. HCl+ Fe3O4 conjugate pairs

The conjugate pairs of the reaction HCl with Fe3O4 is the conjugate base of acid which is chloride ion and oxide is the protonic size of the molecule along with iron cation.

  • Conjugate pair of HCl = Cl
  • Conjugate pair of Fe3O4 = HFe3O4+

7. HCl and Fe3O4 intermolecular forces

The intermolecular force present in HCl is the strong electrostatic force between proton and chloride ion due to tát polarity. In the case of Fe3O4, there is only ionic interaction present along with covalent force as the molecule is non-polar.

MoleculeActing force
van der waal
Intermolecular Force of
Reatants and Products

8. HCl + Fe3O4 reaction enthalpy

The total reaction enthalpy for the reaction HCl and Fe3O4 is calculated by the formula, the enthalpy of the product – enthalpy of the reactants.

Enthalpy of
Reactants and Products

So, the total enthalpy change for the reaction is, +444 kJ/mol =[(-341.8)+2*(-399.5)+4*(-68)] – [(-1118.4)+8*(-92.3)] , which is positive value.

9. Is HCl + Fe3O4 a buffer solution?

The reaction between HCl and Fe3O4 does not give any buffer solution because Fe3O4 is not a basic salt.

Redox Schematic Of
HCl and Fe3O4

10. Is HCl + Fe3O4 a complete reaction?

The reaction between HCl and Fe3O4 is about to tát complete because it forms ferric chloride, ferrous chloride, and H2O after the completion of the reaction.

Fe3O4 + 8HCl = FeCl2 + 2FeCl3 + 4H2O

11. Is HCl + Fe3O4 an exothermic or endothermic reaction?

The reaction between Fe3O4 and HCl is endothermic as per thermodynamics because we get a positive enthalpy change for the reaction which denotes reaction absorbs the heat or the energy of the products is much lower kêu ca the energy of reactants. Where δH is always positive.

Energy Diagram profile of
Endothermic reaction

12. Is HCl + Fe3O4 a redox reaction?

The reaction of HCl and Fe3O4 is a redox reaction where the chlorine atoms get reduced and iron gets oxidized due to tát the mixed valence oxide and the oxygen atom gets oxidized here.

13. Is HCl + Fe3O4 a precipitation reaction

In the reaction between HCl and Fe3O4, one of the products formed is ferrous chloride which is precipitated in the solution and exists at the lower part of the conical flask.

14. Is HCl + Fe3O4 reversible or irreversible reaction?

The reaction between HCl and Fe3O4 is also irreversible as it can proceed only forward.

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Irreversible Reaction

15. Is HCl + Fe­3O4 displacement reaction?

The above reaction between HCl and Fe3O4 is a double displacement reaction where chlorine from the acid part is displaced to tát ferrous and ferric chloride molecules and iron is also displaced from its oxide to tát produce salt and water.


We conclude that the reaction of HCl with Fe3O4 gives us two mixed valence chloride molecules where iron shows +2 and +3 oxidation states. Because Fe3O4 is a spinel complex in organometallic chemistry.

Read more about Facts on HCl + CaOCl2, Facts on HCl + Ag and Facts on HCl + AgCl.