15 Facts on HCl + MgSO3: What, How To Balance & FAQs

HCl is one of the important mineral acids and MgSO3 is an alkaline earth metal sulfite salt. Let us focus on the essential facts on how HCl and MgSO3 react to each other.

HCl or hydrochloric acid reacts with MgSO3 or magnesium sulfite, which is the sulfite salt of magnesium. The sulfite salt remains in hexahydrate form mainly and its anhydrous form can readily absorb water in presence of air.

This article will generate some idea about all the essential characteristics of the reaction HCl + MgSO3.

What is the product of HCl and MgSO3

The products of HCl + MgSO3 are magnesium chloride (MgCl2), sulfur dioxide (SO2), and water (H2O). The first produced product, sulfurous acid (H2SO3), being an unstable compound, readily decomposes into SO2 and H2O.

Reaction between HCl and MgSO3

What type of reaction is HCl + MgSO3

HCl + MgSO3 is a type of double displacement reaction as reactant ions are exchanging their positions while forming products.

How to balance HCl + MgSO3

The equation for the reaction HCl + MgSO3 is

HCl + MgSO3 =  MgCl2 + SO2 + H2O

The balanced equation is obtained by following the steps mentioned below.

  • In the above equation, the number of Mg, S, and O atoms are the same before and after the reaction.
  • HCl + MgSO3 = MgCl2 + SO2 + H2O
  • For both H and Cl atoms, their number of atoms is 1 and 2 respectively before and after the reaction.
  • HCl  +  MgSO3  = MgCl2 + SO2 + H2O
  • Multiply HCl by 2 to make the number of H and Cl atoms 2 on both sides.
  • Thus the balanced equation is
  • 2HCl + MgSO3 =  MgCl2 + SO2 + H2O

HCl + MgSO3 titration

Back titration is required to get the amount of the poorly insoluble salt MgSO3 in the titration between HCl and MgSO3.


Conical flask, pipette, volumetric flask, measuring cylinder, titration stand, and burette.


Phenolphthalein is used as an indicator here.


  • Take MgSO3 salt in a conical flask and add excess HCl of known concentration and volume using a pipette.
  • Combine it thoroughly and add a few drops of phenolphthalein.
  • Titrate the unreacted acid left after the reaction, with NaOH solution of known concentration from a burette.
  • Continue the process until the color converts to light pink.
  • Repeat the procedure 2-3 times to avoid errors.
  • Record all the burette readings.
  • Finally, using the formula S1V1 = S2V2, the amount of unreacted HCl is calculated.
  • From the amount of HCl reacted with MgSO3, the amount of MgSO3 is determined.

HCl + MgSO3 net ionic equation

The net ionic equation for the reaction HCl + MgSO3 is

2H+ (aq) + SO32− (aq)  → H2O (l) + SO2 (g)

Follow the steps mentioned below in order to get the net ionic equation,

  • The two reactants, HCl and MgSO3, and one of the products, MgCl2, being ionic, will dissociate into ions.
  • The complete ionic equation is
  • 2H+ (aq) + 2Cl (aq) + Mg2+ (aq) + SO32− (aq) = Mg2+ (aq) + 2Cl (aq) + H2O (l) + SO2 (g)
  • After erasing the spectator ions (Cl and SO32−) from both sides, we get the net ionic equation, which is-
  • 2H+ (aq) + SO32− (aq) → H2O (l) + SO2 (g)

HCl + MgSO3 conjugate pairs

In the reaction HCl + MgSO3,

  • The conjugate pair of HCl is Cl.
  • The conjugate pair of MgSO3 is not possible as it is a salt.

HCl + MgSOintermolecular forces

In the reaction HCl + MgSO3, the intermolecular forces present are-

  • London dispersion forces and dipole-dipole; are the intermolecular forces present in HCl; the second one is more significant among these two because of its polar nature.
  • Electrostatic force of attraction is present in MgSO3 as it is ionic in nature.

HCl + MgSO3 reaction enthalpy

For HCl + MgSO3, the reaction enthalpy value cannot be calculated as the enthalpy of formation value of MgSO3 is not available in the database.

CompoundsEnthalpy of formation (kJ/mole)
HCl (aq)-167.2
MgSO3 (s)
MgCl2 (aq)-796.9
SO2 (g)-296.8
H2O (l)-285.8
Table representing enthalpy of formation values of all compounds

Is HCl + MgSO3 a buffer solution

HCl + MgSO3 cannot produce a buffer solution as in a buffer solution, strong acids like HCl cannot be present.

Is HCl + MgSO3 a complete reaction

HCl +  MgSO3 is a complete reaction as further reaction is impossible after product formation.

Is HCl + MgSO3 an exothermic or endothermic reaction

HCl +  MgSO3 is whether exothermic or endothermic that cannot be predicted during the reaction as the enthalpy of formation value of MgSO3 is unavailable in the database.

Is HCl + MgSO3 a redox reaction

HCl +  MgSO3 is not a redox reaction as the atoms present in the reactants and product molecules are having same oxidation states throughout the reaction.

Is HCl + MgSO3 a precipitation reaction

HCl + MgSO3 is not a precipitation reaction as the product MgClis a water-soluble solid, and there is no question of precipitation for SO2 and H2O as they are gas and liquid respectively.

Is HCl + MgSO3 reversible or irreversible reaction

HCl + MgSO3 is an irreversible reaction as it is unidirectional in nature.

Is HCl + MgSO3 displacement reaction

HCl + MgSO3 is a displacement reaction as chloride and sulfite ions are swapped between HCl and MgSO3.


In conclusion, the product MgCl2 is a white, crystalline ionic compound consisting of Mg2+ cation and Cl anion. SO2 is an oxide of sulfur having a strong odor.