15 Facts on H2SO3 + KMnO4: What, How To Balance & FAQs

KMnO4 is a strong oxidizing agent so it can easily react with H2SO3 under normal conditions. Let us see the mechanism behind the reaction between H2SO3 and KMnO4.

Potassium permanganate is a purple color solid molecule and makes a solution for using this reagent. Due to its characteristics and color change with pH, it acts as a self-indicator in any type of titration. Sulfurous acid is a strong reducing agent and it can reduce other elements and undergo self-oxidation.

The reaction between H2SO3 and KMnO4 does not require any catalyst because KMnO4 acts here as a self-catalyst. Let us discuss the mechanism of the reaction between sulfuric acid and iron, the reaction enthalpy, the type of reaction, product formation, etc in the following part of the article.

1. What is the product of H2SO3 and KMnO4?

H2SO3 and KMnO4 are reacted together to give Manganese sulfate and Potassium sulfate along with some water molecules and sulfuric acid.

H2SO3 + KMnO4 = MnSO4 + K2SO4 + H2SO4 + H2O

2. What type of reaction is H2SO3 + KMnO4?

H2SO3 + KMnO4 reaction is an example of a double displacement reaction along with redox and precipitation reactions. It is also an acid production reaction along with a hydrolysis reaction.

3. How to balance H2SO3 + KMnO4?

H2SO3 + KMnO4 reaction should be balanced in the following way,

  • Labelling all the reactants and products by the required number of alphabets
  • First, we labeled all the reactants and products by A, B, C, D, E, and F as there are six different atoms obtained for this reaction and the reaction looks like
  • A H2SO3 + B KMnO4 = C MnSO4 + D K2SO4 + E H2SO4 + F H2O
  • Equating all the Coefficients for all the same type of elements by rearranging them.
  • After the rearrangement of all the coefficients of the same elements by their stoichiometric proportion we get,
  • H = 2A = 2E = 2F, S = A = C = D = E, O = 3A = 4B = 4C = 4D = 4E = F, Mn = B = C, K = B = 2D.
  • Using Gaussian elimination to determine the coefficient values
  • Using the Gaussian elimination and equating all the equations we get, A = 5, B = 2, C = 2, D = 1, E = 2, and F= 3,
  • Now write the whole equation in the balanced form
  •  The overall balanced equation will be,
  • 5 H2SO3 + 2 KMnO4 = 3 MnSO4 + K2SO4 + 2 H2SO4 + 3 H2O

4. H2SO3 + KMnO4 titration

To estimate the quantity of potassium or manganese we can perform a titration between KMnO4 and H2SO3.

Apparatus used

We need a burette, conical flask, burette holder, volumetric flask, and beakers for this titration.

Titre and titrant

H2SO3 versus KMnO4, H2SO3 acts as a titrant taken in the burette and the molecule to be analyzed is KMnO4 taken in a conical flask.

Indicator

The whole titration is done in acidic pH as the concentration of H2SO3 is high and for this reaction, KMnO4 acts as a self-indicator because it is a colored solution and changes in different pH.

Procedure

The burette was filled with standardized H2SO3 and KMnO4 was taken in a conical flask along with the respective indicator. H2SO3 is added dropwise to the conical flask and the flask was shaking constantly. After a certain time when the endpoint arrived KMnO4 changes its color.

5. H2SO3+ KMnO4 net ionic equation

The net ionic equation between H2SO3 + KMnO4 is as follows,

H+(aq.) + OH(aq.) + SO2(g) + K+(aq.) + MnO4(aq.) = Mn2+(aq.) + SO42-(aq.) + K+(aq.) + H+(aq.) + OH(aq.)

  • To derive the net ionic equation the following steps are required,
  • First, we ionized all the possible compounds in their existing state.
  • After that, H2SO3 will be ionized in proton and sulfite ions as it is a strong electrolyte
  • After that KMnO4 also dissociated to K+ ion and MnO4.
  • After that, the product MnSO4 also dissociated to Mn2+ which is d5 stable configuration and corresponding SO42-.
  • Water is also ionized to H+ and OH-.
  • SO2 is an existing gaseous form so it cannot be ionized.

6. H2SO3+ KMnO4 conjugate pairs

H2SO3 + KMnO4 reaction has the following conjugate pairs,

  • Conjugate pair of H2SO3 = SO32-
  • Conjugate pair of OH = H2O
  • Conjugate pairs of SO42- = H2SO4

7. H2SO3 and KMnO4 intermolecular forces

H2SO3 + KMnO4 reaction has the following intermolecular forces,

  • The intermolecular force between H2SO3 is an electrostatic, covalent force.
  • For the KMnO4 it is ionic interaction and for MnSO4 and K2SO4 the ionic interaction is along with the coulombic force.
  • H-bonding is present in water and van der waal’s force and London dispersion force are present in SO2. 
MoleculeActing
force
H2SO3 / H2SO4Electrostatic,
Covalent,
Dipole
interaction
KMnO4Ionic, metallic, and
electrostatic
K2SO4 / MnSO4Coulombic force, strong
ionic interaction
H2OCovalent,
H-bonding
SO2Van der Waal’s force,
London force
Intermolecular Forces

8. H2SO3 + KMnO4 reaction enthalpy

In H2SO3 + KMnO4 reaction enthalpy is -6112.25 KJ/mol which can be obtained by the formula enthalpy of products – enthalpy of reactants, and here the change in enthalpy is negative.

MoleculeEnthalpy
(KJ/mol)
KMnO4-813
H2SO4-814
MnSO4-1130
K2SO4-1437.8
H2O-68
H2SO3+52.89
Enthalpy of Reactants
and Products

9. Is H2SO3 + KMnO4 a buffer solution?

H2SO3 + KMnO4 reaction gives a buffer solution of K2SO4 and H2SO4 and they can control the pH of the solution. Because the latter is acid so it can control the pH after adding a base.

10. Is H2SO3 + KMnO4 a complete reaction?

H2SO3 + KMnO4 reaction is the complete reaction because it gives three complete products MnSO4, K2SO4, and H2SO4 along with water molecules. The reaction takes need some time to complete until all the reactants completely reacted the products are not formed.

11. Is H2SO3 + KMnO4 an exothermic or endothermic reaction?

The reaction H2SO3 + KMnO4 is exothermic in terms of thermodynamics first law. So, the reaction released more energy and temperature to the surroundings so we have to be more cautious, Where, δH is always negative.

12. Is H2SO3 + KMnO4 a redox reaction?

The reaction between H2SO3 + KMnO4 is a redox reaction because in this reaction Mn gets reduced whereas sulfur gets oxidized. In this reaction, KMnO4 acts as an oxidizing agent whereas H2SO3 acts as a reducing agent.

Screenshot 2022 12 02 120013
Redox Schematic of the
H2SO3 and KMnO4 Reaction

13. Is H2SO3 + KMnO4 a precipitation reaction

The reaction H2SO3 + KMnO4 is a precipitation reaction because K2SO4 and MnSO4 get precipitated in the solution at acidic pH and are not soluble in the reaction mixture.

14. Is H2SO3 + KMnO4 reversible or irreversible reaction?

The reaction between H2SO3+ KMnO4 is reversible because we get SO2 gas when H2SO3 dissociated. When gas is formed during the reaction the entropy of the reaction increases and the equilibrium of the reaction shifts towards the left-hand side also.

5 H2SO3 + 2 KMnO4↔3 MnSO4 + K2SO4 + 2 H2SO4 + 3 H2O

H2SO3 = H2O + SO2

15. Is H2SO3 + KMnO4 displacement reaction?

The reaction between H2SO3+ KMnO4 is an example double displacement reaction because in the above reaction Mn and K are displaced by H+ in H2SO3 forming corresponding sulfate and both cations also displaced H+ and formed H2SO4.

Screenshot 2022 12 02 120027
Double Displacement Reaction

Conclusion

In the reaction between KMnO4 and H2SO3 gives us sulfuric acid as one of major product so it can be used in industry for production of acid. This reaction also produced two ionic salt so it is more important reaction in industry as well as chemistry. As it is exothermic and large amount of energy will be produced during the course of reaction so we have to maintain the safety.