15 Facts on H2SO3 + Fe(OH)3: What, How To Balance & FAQs

Ferric hydroxide [Fe(OH)3] is a transition metal base and it reacts with sulfurous acid. Let us discuss the products obtained from the reaction between Fe(OH)3 and H2SO3.

H2SO3 and Fe(OH)3 react with each other and form ferric sulfite [Fe2(SO3)3] and water. Fe(OH)3 is a weak base and H2SO3 is also a weak acid. They undergo a neutralization reaction to form salt and water.

This article focuses on the products, enthalpy change, type, balancing method, conjugate pairs, intermolecular forces, and some more relevant topics of the reaction.

What is the product of H2SO3 and Fe(OH)3?

Ferric hydroxide, Fe(OH)3 reacts with the weak acid, H2SO3, and produces ferric sulfite [Fe2(SO3)3] and water (H2O).

2Fe(OH)3 (aq) + 3H2SO3 (aq) =  Fe2(SO3)3 (aq) + 6H2O (l)

What type of reaction is H2SO3 + Fe(OH)3?

The reaction between H2SO3 + Fe(OH)3 is one type of-

How to balance H2SO3 + Fe(OH)3?

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

  • Write the unbalanced chemical equation first using a right arrow sign as it is not balanced yet. Fe(OH)3 (aq) + H2SO3 (aq)  Fe2(SO3)3 (aq) + H2O (l)
  • The mole numbers of each of the reacting elements should be determined on the reactant and product side.
ElementsMole numbers on the reactant sideMole numbers on the product side
Mole numbers of the reacting elements on reactant and product side
  • To balance both sides (reactant and product) we have to multiply 2 with the mole number of Fe(OH)3, 3 with H2SO3 on the reactant side, and 6 with the mole number of H2O on the product side.
  • Therefore, the balanced equation will be – 2Fe(OH)3 (aq) + 3H2SO3 (aq) =  Fe2(SO3)3 (aq) + 6H2O (l)

H2SO3 + Fe(OH)3 Titration

The titration between H2SO3 + Fe(OH)3 is not possible because H2SO3 is a weak acid and Fe(OH)3 is a weak base. The titration between a weak acid and a weak base is not possible because the equivalence point cannot be detected with accuracy due to not getting any sharp change in the titration curve.

H2SO3 + Fe(OH)3 Net Ionic Equation

The net ionic equation of the chemical reaction H2SO3 + Fe(OH)is

2Fe3+ (aq) + 3OH (aq) + 6H+  + 3SO32- (aq) =  2Fe3+(aq) + 3SO32- (aq) + 6H2O (l)

H2SO3 + Fe(OH)3 Conjugate Pairs

The conjugate pairs (pair of compounds differ by one proton) equation of H2SO3 + Fe(OH)is-

  • The conjugate pair of  H2SO3 is HSO3
  • The conjugate pair of H2O is OH

H2SO3 + Fe(OH)3 Intermolecular Forces

The intermolecular forces act on H2SO3 + Fe(OH)are-

  • The electrostatic force of attraction is working in Fe(OH)3. In the lattice of ferric hydroxide, the ferric ion (Fe3+), and hydroxyl ion (OH) are attracted by each other by this strong interionic Columbic force.
  • Being a covalent compound, dipole-dipole interaction and London dispersion forces are present in H2SO3. It can also form a very strong intermolecular hydrogen bonding with water molecules as well as itself.
  • One of the products, ferric sulfite is ionic, and water is a covalent molecule. Therefore, the above intermolecular forces are also present between them.

H2SO3 + Fe(OH)3 Reaction Enthalpy

The enthalpy of the reaction H2SO3 + Fe(OH)3 are written below-

Chemical compoundFormation enthalpy
H2SO3-552 KJ/mol (????H gas)
-600.45 KJ/mol ( ????H liquid)
Fe(OH)3-824 KJ/mol
H2O-286 KJ/mol
Enthalpy of the reactants and products

Is H2SO3 + Fe(OH)3 a buffer solution?

H2SO3 + Fe(OH)is not a buffer solution because it is not a mixture of either a weak acid and its conjugate base (CH3COOH and CH3COONa, acidic buffer) or a weak base and its conjugate acid (NH4OH and NH4Cl, basic buffer). In this mixture, H2SO3 is a weak acid, and Fe(OH)acts as a weak base.

Is H2SO3 + Fe(OH)3 a complete reaction?

Only H2SO3 + Fe(OH)cannot be a complete reaction because it is only the reactants written here. If the actual products which are water and ferric sulfite are also written along with the reactants then it will be considered a complete reaction. Therefore, the complete reaction is written below-

2Fe(OH)3 (aq) + 3H2SO3 (aq) = Fe2(SO3)3 (aq) + 6H2O (l)

Is H2SO3 + Fe(OH)3 an exothermic or endothermic reaction?

H2SO3 + Fe(OH)3 is considered to be an exothermic reaction because the enthalpy of the neutralization is always exothermic. The energy released due to the formation of water molecules is greater than the energy absorbed for the progress of the reaction.

h2so3 + fe(oh)3
Energy diagram of an exothermic reaction

Is H2SO3 + Fe(OH)3 a redox reaction?

H2SO3 + Fe(OH)3 is not a redox reaction because in this reaction no electron transfer is taking place. Therefore, there is no change in the oxidation state of Fe, H, O, and S. All the elements maintain their oxidation state throughout the reaction.

ElementsOxidation state on the reactant sideOxidation state on the product side
Oxidation state of the elements

Is H2SO3 + Fe(OH)3 a precipitation reaction?

H2SO3 + Fe(OH)3 is not a precipitation reaction because none of the two products (ferric sulfite and water) are obtained as a precipitate after the completion of the reaction. The product, ferrous sulfite [Fe2(SO3)3] is completely soluble in water. It is rather a displacement reaction.

Is H2SO3 + Fe(OH)3 a reversible or irreversible reaction?

H2SO3 + Fe(OH)3 is an irreversible reaction because the product side is more stable than the reactant side. Besides that, it is a neutralization reaction, and all the neutralization reaction becomes irreversible due to the formation of more stable salt and water.

Is H2SO3 + Fe(OH)3 displacement reaction?

H2SO3 + Fe(OH)3 is a double-displacement reaction because each of the reacting chemicals is displaced by each other to form the products. In this reaction, Fe is displaced by hydrogen from ferric hydroxide whereas hydrogen is displaced by Fe from sulfurous acid.

Double Displacement Reaction H2SO3 FeOH3
Double Displacement Reaction


Ferric hydroxide acts as an iron supplement in the living body and helps to cure iron deficiency anemia. Sulfurous acid also has different uses in the manufacture of fertilizers, dyes detergents, inorganic salts, etc.

Read more about following H2SO3 facts

H2SO3 + Al
H2SO3 + Al(OH)3
H2SO3 + CuS
H2SO3 +KClO3
H2SO3 + O2
H2SO3 + BaCl2
H2SO3 + Ba(OH)2
H2SO3 + K2O
H2SO3 + CaO
H2SO3 + Ca(OH)2
H2SO3 + CaCl2
H2SO3 + HgO
H2SO3 + BaCO3
H2SO3 + Mn(OH)2
H2SO3 + AgOH
H2SO3 + Fe(OH)3
H2SO3 + K
H2SO3 + LiOH
H2SO3 + Fe2O3
H2SO3 + NaHCO3
H2SO3 + Ca
H2SO3 + CsOH
H2SO3 + Ag2S Reaction
H2SO3 + Hg(OH)2
H2SO3 + AL2O3
H2SO3 + KIO3
H2SO3 + FeCO3
H2SO3 + Zn(OH)2
H2SO3 + NH3
H2SO3 + Na2CO3
H2SO3 + CaCO3
H2SO3 + CuO
H2SO3 + KMnO4
H2SO3 + FeCl2
H2SO3 + AlBr3
H2SO3 + NaHSO3
H2SO3 + Na
H2SO3 + Br2