15 Facts on H2SO3 + Fe2O3: What, How To Balance & FAQs

Ferric oxide (Fe₂O₃) is a transition metal oxide, and it reacts with weak sulfurous acid. Let us explore the products obtained from the reaction of Fe₂O₃ + H₂SO₃.

Fe₂O₃ is an amphoteric oxide having both acidic and basic character. Sulfurous acid (H₂SO₃) is a weak acid, and both of them undergo a neutralization reaction at ambient temperature and pressure.

This article focuses on the products, balancing method, reaction enthalpy, and reversibility with some more relevant topics of the reaction between H₂SO₃ and Fe₂O₃ in detail.

What is the product of H₂SO₃ and Fe₂O₃?

Ferric sulfite [Fe₂(SO₃)₃] along with water (H₂O) are obtained as the products of the reaction between sulfurous acid (H₂SO₃) and ferric oxide (Fe₂O₃).

Fe₂O₃ (aq) + 3H₂SO₃ (aq) =  Fe₂(SO₃)₃ (aq) + 3H₂O (l)

What type of reaction is H₂SO₃ + Fe₂O₃?

The chemical reaction, H₂SO₃ + Fe₂O₃ is one type of-

• Acid-base reaction or neutralization reaction
• Irreversible reaction
• Exothermic reaction
• Double-displacement reaction

How to balance H₂SO₃ + Fe₂O₃?

The following steps should be followed to balance a chemical reaction-

• Write the unbalanced chemical equation first using a right arrow sign to signify that the reaction is not balanced yet. Fe₂O₃ (aq) + H₂SO₃ (aq) → Fe₂(SO₃)₃ (aq) + H₂O (l)
• The mole numbers of each of the reacting elements should be determined on both the reactant and product sides.

Elements	Mole numbers on the reactant side	Mole numbers on the product side
Fe	2	2
S	1	3
O	6	10
H	2	2

• To balance both sides (reactant and product) we have to multiply 3 with the mole number of H₂SO₃ on the reactant side and 3 with the mole number of H₂O on the product side.
• Therefore, the final and the balanced equation will be – Fe₂O₃ (aq) + 3H₂SO₃ (aq) = Fe₂(SO₃)₃ (aq) + 3H₂O (l)

H₂SO₃ + Fe₂O₃ Net Ionic Equation

The net ionic equation of the reaction H₂SO₃ + Fe₂O₃ is-

2Fe³⁺ (aq) + 3O^2- (aq) + 6H⁺  + 3SO₃^2- (aq) =  2Fe³⁺(aq) + 3SO₃^2- (aq) + 3H₂O (l)

H₂SO₃ + Fe₂O₃ Conjugate Pairs

The conjugate pairs (pair of compounds differ by one proton) of H₂SO₃ + Fe₂O₃ is –

• The conjugate pair of  H₂SO₃ is HSO₃^–
• The conjugate pair of H₂O is OH^–
• There is no existence of conjugate pairs of ferric oxide as well as ferric sulfite.

H₂SO₃ + Fe₂O₃ Titration

The acid-base titration of H₂SO₃ + Fe₂O₃ cannot be performed because it is the reaction between a weak acid and an amphoteric oxide (a weak base). In this type of titration, the detection of the equivalence point is not possible as there is no sharp change in the titration graph of the weak acid and the weak base.

H₂SO₃ + Fe₂O₃ Intermolecular Forces

The intermolecular forces present in the reaction of H₂SO₃ + Fe₂O₃ is-

• Fe₂O₃ and H₂SO₃ is ionic compound on the reactant side. Therefore, the Columbic attraction force is working between ferric ion (Fe³⁺) and oxide ion (O^2-) in the lattice of ferric oxide and hydrogen ion and sulfite ion (SO₃^2-) in H₂SO₃. These two ions are attached by this electrostatic attraction force
• H₂O is a covalent compound. Thus, dipole-dipole force and London dispersion forces are present in sulfurous acid molecules. Besides that, it can also form strong intermolecular hydrogen bonding with other H₂SO₃ molecules.

H₂SO₃ + Fe₂O₃ Reaction Enthalpy

The enthalpy of the reaction H₂SO₃ + Fe₂O₃ are written below-

Chemical compound	Formation enthalpy
H2SO3	-552 KJ/mol (gas) -600.45 KJ/mol (liquid)
Fe2O3	-824.2 KJ/mol
H2O	-286 KJ/mol

Is H₂SO₃ + Fe₂O₃ a buffer solution?

H₂SO₃ + Fe₂O₃ is not a buffer solution because neither it is a mixture of a weak acid and its conjugate base (CH₃COOH and CH₃COONa, acidic buffer) nor a weak base and its conjugate acid (NH₄OH and NH₄Cl, basic buffer). H₂SO₃ is a weak acid and Fe₂O₃ is an amphoteric oxide that acts as a weak base.

Is H₂SO₃ + Fe₂O₃ a complete reaction?

H₂SO₃ + Fe₂O₃ cannot be a complete reaction because it is only the reactants written here. It will be considered a complete reaction if the reactants along with the products, ferric sulfite [Fe₂(SO₃)₃] and water (H₂O), are written here. Therefore, the complete reaction will be –

Fe₂O₃ (aq) + 3H₂SO₃ (aq) =  Fe₂(SO₃)₃ (aq) + 3H₂O (l)

Is H₂SO₃ + Fe₂O₃ an exothermic or endothermic reaction?

H₂SO₃ + Fe₂O₃ is an exothermic reaction because the change of enthalpy is negative. In an exothermic reaction, heat is absorbed on the product side and generated on the reactant side and the amount of heat absorbed on the product side is always greater than the amount of heat generated on the reactant side.

Is H₂SO₃ + Fe₂O₃ a redox reaction?

H₂SO₃ + Fe₂O₃ is not a redox reaction because this reaction does not involve any electron transfer. Therefore, no change of oxidation state is taking place. Reacting elements (Fe, S, O and H) do not change their oxidation state from the reactant side to the product side.

Elements	Oxidation state on the reactant side	Oxidation state on the product side
Fe	+3	+3
H	+1	+1
S	+4	+4
O	-2	-2

Is H₂SO₃ + Fe₂O₃ a precipitation reaction?

The chemical reaction, H₂SO₃ + Fe₂O₃ is not a precipitation reaction because no precipitation of any compound appears on the product side. ferric sulfite [Fe₂(SO₃)₃] is not obtained as a precipitate after the completion of the reaction and it becomes soluble in water.

Is H₂SO₃ + Fe₂O₃ a reversible or irreversible reaction?

The reaction, H₂SO₃ + Fe₂O₃ is an irreversible reaction due to obtaining more stable products. It is a neutralization reaction and all the neutralization reactions become irreversible due to the formation of more stable salt and water than its corresponding acid and base on the reactant side.

Is H₂SO₃ + Fe₂O₃ displacement reaction?

The reaction, H₂SO₃ + Fe₂O₃ is a double-displacement reaction. In this reaction, iron is replaced by hydrogen from ferric oxide, and hydrogen itself is replaced by iron from sulfurous acid to obtain the products. Due to happening two displacements, it is defined as a double-displacement reaction.

Conclusion

Sulfurous acid has some significant applications in the manufacturing industry of fertilizers, dyes detergents, inorganic salts, etc. Ferric oxide is used as the major feedstock of iron production. It is also used in cosmetics and dental composites.