15 Facts on H2SO3 + Br2: What, How To Balance & FAQs

Sulfurous acid(H₂SO₃) is a water-soluble acid, and Bromine(Br₂) is a volatile diatomic molecule. Let us explore more about their reaction.

Sulfurous acid is also known as trioxo-sulfuric acid, it is a colourless liquid and weaker acid than sulfuric acid. Bromine appears to be a reddish-brown liquid at room temperature, having a density of 3.1028 g/cm³.

The article below will cover some important aspects of the reaction between H₂SO₃ and Br₂.

What is the product of H₂SO₃ and Br₂?

H₂SO₃ reacts with Br₂ to give Dithionic acid(H₂S₂O₆) and Hydrobromic acid (HBr).

2H₂SO₃ + Br₂ → H₂S₂O₆ + 2HBr

What type of reaction is H₂SO₃ + Br₂?

The reaction of H₂SO₃ + Br₂ is an oxidation-reduction reaction.

How to balance H₂SO₃ + Br₂?

To balance the H₂SO₃ + Br₂ reaction, the following steps are to be followed.

H₂SO₃ + Br₂ → H₂S₂O₆ + HBr

• Count the number of atoms present on the reactant and product sides.

Elements involved	Reactants side	Products side
H	2	3
O	1	2
S	3	6
Br	2	1

• Multiply with significant numbers to the specific reactants and products such that the number of each atom on the reactant side and the product side becomes equal.
• 2× H₂SO₃ on reactant side and 2 × HBr on the product side.
• Count the number of atoms after the multiplication process to ensure an equal number of atoms on both sides.

Elements involved	Reactants side	Products side
H	4	4
S	2	2
O	6	6
Br	2	2

• write the complete balanced chemical equation.
• The balanced chemical equation is
• 2H₂SO₃ + Br₂ = H₂S₂O₆ + 2HBr

H₂SO₃ + Br₂ titration

Titration of H₂SO₃ + Br₂ is not possible because H₂SO₃ is an acid so it will be titrated only by a strong base like NaOH, not with Br₂.

H₂SO₃ + Br₂ net ionic equation

The net ionic equation of the reaction is-

Br_2(aq) + 2SO₃^2- _(aq) = 2Br^–_(aq)+ S₂O₆^2-_(aq) 

The net ionic equation is obtained by using the steps below.

• Write the balanced chemical reaction
• 2H₂SO₃ + Br₂ = H₂S₂O₆ + 2HBr
• H₂SO₃, HBr and H₂S₂O₆ dissociates in aqueous media as
• H₂SO₃ = 2H⁺_(aq) + SO₃^2-_(aq) 
•  HBr = H⁺_(aq) + Br^–_(aq) and
• H₂S₂O₆ = 2H⁺ _(aq)+ S₂O₆^2- _(aq).
• So, the complete ionic equation is
• Br_2(aq) +4H⁺_(aq) + 2SO₃^2- _(aq) = 2Br^–_(aq)+ S₂O₆^2-_(aq) + 4H⁺_(aq) 
• 4H⁺ gets cancelled out from both sides.
• And the net ionic equation becomes:
• Br_2(aq) + 2SO₃^2- _(aq) = 2Br^–_(aq)+ S₂O₆^2-_(aq) 

H₂SO₃ + Br₂ conjugate pairs

The conjugate pairs of H₂SO₃ + Br₂ reaction are

Compounds	Conjugate acid	Conjugate base
H2SO3 +   H2O  →	H3O+ (aq)	HSO3–(aq)
HSO3––+   H2O  →	H3O+ (aq)	SO32-(aq)
H2S2O6 +   H2O  →	H3O+ (aq)	S2O62– (aq)
HBr + H2O  →	H3O+ (aq)	Br-

H₂SO₃ and Br₂ intermolecular forces

The intermolecular forces of the reaction H₂SO₃ + Br₂ are:

• H₂SO₃ molecule has hydrogen bonding tendency, dipole-dipole interaction and ion-dipole interaction.
• Br2 is a nonpolar molecule and thus possesses London dispersion force.
• HBr is an ionic molecule and has ionic interaction.
• H₂S₂O₆ shows dipole-dipole interaction and Hydrogen bonding interaction.

H₂SO₃ + Br₂ reaction enthalpy

The enthalpy of the reaction H₂SO₃ + Br₂ is not available in literature. For dithionic acid(H₂SO₃) ΔH⁰_f (enthalpy of formation) value is not experimentally calculated.

Is H₂SO₃ + Br₂ a buffer solution?

H₂SO₃ + Br₂ is not a buffer solution because H₂SO₃ + Br₂ is a mixture of a weak acid(H₂SO₃) and a Lewis acid ( Br₂) whereas buffer solution is made by mixing weak acid and its conjugate base or weak base and its conjugate acid.

Is H₂SO₃ + Br₂ a complete reaction?

The H₂SO₃ + Br₂ reaction is a complete reaction, no further reaction is possible here.

Is H₂SO₃ + Br₂ an exothermic or endothermic reaction?

The exothermic and endothermic nature of the H₂SO₃ + Br₂ reaction can not be specified without knowing the reaction enthalpy.

Is H₂SO₃ + Br₂ a redox reaction?

H₂SO₃ + Br₂ reaction is a redox reaction because here, sulfur of H₂SO₃ is oxidized from +4 to +5 oxidation state, and H₂SO₃ reduces bromine from 0 to -1 oxidation state.

Is H₂SO₃ + Br₂ a precipitation reaction?

H₂SO₃ + Br₂ reaction is not a precipitation reaction because the products dithionic acid(H₂SO₃) and hydrobromic acid(H₂SO₃) are soluble in water and so do not form precipitate.

Is H₂SO₃ + Br₂ reversible or irreversible reaction?

The H₂SO₃ + Br₂ reaction is a reversible reaction because it can undergo the reverse reaction also:

H₂S₂O₆(aq) + 2HBr(aq) = 2H₂SO₃(aq) + Br₂(aq)

Is H₂SO₃ + Br₂ displacement reaction?

The H₂SO₃ + Br₂ reaction is not a displacement reaction as no accountable ion displacement has taken place there.

Conclusion

Sulfurous acid is a weak acid and is used in pigments, dyes, and as a reducing agent. Bromine-bearing chemicals are used in agriculture industries. Dithionic acid is water soluble and used as a gentle oxidizing and reducing agent.