15 Facts on HCl + Mn3O4: What, How To Balance & FAQs

Mn3O4, known as Trimanganese tetraoxide, is a mixed oxide and hydrochloric acid (HCl) is a strong acid with a pungent smell. Let us look into the reaction HCl+Mn3O4 in details.

Hydrochloric acid is corrosive by nature, and when it reacts with Mn3O4 gives a gas and a reduced manganese salt. Mn3O4 is an oxide with a spinel structure containing one Manganese in a +2 oxidation state and the other two in +3 oxidation state, often represented as MnO.Mn2O3.

Here, we will examine the products, intermolecular forces, and, enthalpy associated with the reaction of Mn3O4 and HCl in detail.

What is the product of HCl and Mn3O4

When Mn3O4 reacts with HCl it gives MnCl2 (Manganese dichloride), Chlorine gas (Cl2), and water molecules as by-products.

Mn3O4 + HCl → MnCl2 + Cl2 + H2O

What type of reaction is HCl + Mn3O4

The Mn3O4 + HCl reaction is a redox reaction as Manganese is reduced and chlorine is getting oxidized.

How to balance HCl + Mn3O4

The Mn3O4 + HCl reaction can be balanced by the following steps,

Redox reaction
  • First, we need to indicate the elements undergoing reduction and oxidation respectively.
  • The equation is divided into two halves. Here, in Mn3O4 two Manganese that are present in the +3 oxidation state are reduced to the +2 oxidation state, and chlorine is oxidized.
  • 1. Reduction: Mn+2Mn2+3 + 2e → 3Mn+2
  • 2. Oxidation: 2Cl → Cl2 + 2e
  • The charges are balanced so the equation is given by,
  • Mn3O4 + 2HCl → 3MnCl2 + Cl2 + H2O
  • The elements are further balanced using coefficients to get the same number of elements on either side of the reaction. The balanced equation becomes,
  • Mn3O4 + 8HCl → 3MnCl2 + Cl2 + 4H2O

HCl + Mn3O4 titration

Mn3O4 solution can be titrated against hydrochloric acid using a suitable indicator.

Apparatus used

Volumetric flask, conical flask, burette, pipette, funnel, and measuring cylinder.


Phenolphthalein indicator is used as the titration is done in the acidic medium.


  • The standardized solution of HCl is taken in the burette.
  • With the help of the pipette, Mn3O4 solution is taken into the conical flask and 2-3 drops of the indicator are added to it.
  • The HCl is added dropwise until a light pink color is obtained, which indicates the endpoint of the reaction from which calculation will be done.

HCl + Mn3O4 net ionic equation

Following steps can be used to write the net ionic equation.

  • The balanced equation is-
  • Mn3O4 + 8HCl → 3MnCl2 + Cl2 + 4H2O
  • The phases (solid, liquid, gas, or aqueous) of the compounds are shown.
  • Mn3O4(s) + 8HCl(aq) → 3MnCl2(aq) + Cl2(g) + 4H2O(l)
  • The strong electrolytes are split into ions. H2O is a weak electrolyte and Mn3O4 is solid so will not split. The equation now becomes,
  • Mn3O4(s) + 8H+(aq) + 8Cl(aq) → 3Mn2+ + 6Cl(aq) + Cl2(g) + 4H2O(l)
  • The spectator ions are canceled out and the net ionic equation is given by,
  • Mn3O4(s) + 8H+(aq) + 2Cl(aq) → 3Mn2+ + Cl2(g) + 4H2O(l)

HCl + Mn3O4 conjugate pairs

The Mn3O4+HCl combination will not make a conjugate pair as they will not conjugate with each other, and Mn3O4 is a mixed oxide so there is no concept of conjugate acid-base pair.

HCl and Mn3O4 intermolecular forces

  • HCl molecule shows London dispersion forces and dipole-dipole interactions as it is a polar compound.
  • Ionic interactions are present in Mn3O4 and it has spinel structure.
Intermolecular forces in HCl

HCl + Mn3O4 reaction enthalpy

The enthalpy of the reaction HCl+Mn3O4 is -87.2 KJ/mol. The enthalpy is calculated using the formula-                      

∆Hf°(reaction) = ∆Hf°(products) – ∆Hf°(reactants)

= – 2808.4 – 2721.2

= -87.2 KJ/mol

Reactants and productsEnthalpies ∆Hf° (KJ/mol)
HCl (aq)-166.9
Cl2 (g)0.0
Enthapies of compounds

Is HCl + Mn3O4 a buffer solution

The HCl+Mn3O4 combination does not function as a buffer solution as Mn3O4 is an oxide rather than a salt and also HCl is a strong acid, not a weak acid.

Is HCl + Mn3O4 a complete reaction

The reaction of Mn3O4 with HCl is a complete reaction as the soluble salt and the gas formed will not react further.

Is HCl + Mn3O4 an exothermic or endothermic reaction

The reaction between Mn3O4 and HCl is an exothermic reaction as it releases heat during the reaction.

Is HCl + Mn3O4 a redox reaction

The HCl-Mn3O4 is a redox reaction as Mn3O4 is acting as an oxidizing agent by oxidizing chlorine and HCl is behaving as a reducing agent by reducing Manganese to a +2 oxidation state.

Is HCl + Mn3O4 a precipitation reaction

The reaction between HCl and Mn3O4 is not a precipitation reaction as the products formed are completely soluble and no precipitate is formed.

Is HCl+ Mn3O4 reversible or irreversible reaction

HCl+Mn3O4 is an irreversible reaction because the products formed during the reaction will not react back to give back the reactants. The chlorine gas formed will be escaped making the forward reaction more feasible.

Is HCl + Mn3O4 displacement reaction

The reaction (HCl + Mn3O4) is not a displacement reaction.


Mn3O4 found as a natural mineral is used as a weighing agent and in the production of ferrites. The salt (MnCl2) formed in the reaction is widely used for manufacturing dry cell batteries.

Read more facts on HCl:

HCl + ZnCO3

Lubna Khan

Hi! I am Lubna Khan. I have done my Postgraduation in Chemistry at Jamia Millia Islamia, New Delhi. I have been in academia for years and have always welcomed new opportunities, lifestyles, and cultures coming my way. Let us connect more at LinkedIn:www.linkedin.com/in/lubna-khan-705477216

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