15 Facts on HCl + MgCO3: What, How To Balance & FAQs

The reaction of colourless HCl acid solution and MgCO3 which is insoluble in water forms a colourless aqueous compound. Let us find out different relevant facts about the reaction.

Hydrochloric acid also referred to as muriatic acid, is a colourless solution categorized as a strong acid, prepared from hydrogen and chloride elements. Magnesium carbonate is an odorless compound present in form of a whitish bulky powder used as a dying agent in food, printing inks, etc.

In the article, we will discuss the reaction mechanism, balancing method, titration and reaction enthalpy.

What is the product of HCl and MgCO3?

HCl reacts with MgCO3 to form Magnesium Chloride, with carbon dioxide and water as by-products, as shown in the following reaction:

MgCO3 + 2HCl → MgCl2 + CO2 + H2O

What type of reaction is HCl + MgCO3?

HCl+ MgCO3 is a neutralization reaction since the reaction of HCL and MgCO3 leads to the formation of salt which is MgCl2.

How to balance HCl + MgCO3?

To balance a chemical reaction, the following steps are to be followed-

  • Step 1: Write down the unbalanced chemical reaction.
  • MgCO3 + HCl → MgCl2 + CO2 + H2O
  • Step 2: Write down the number of moles of each element in the reactant side and product side, as tabulated below,
CompoundsReactant SideProduct Side
Number of moles of each element in the reactant side and product side
  • Step 3: For a balance reaction, the number of moles of each element in the reactant side is equal to the number of elements in the product side, in this case, chlorine and hydrogen moles are unbalanced.
  • Step 4: Multiply HCl with 2 on the reactant side, which balances the reaction.
  • Step 5: Balanced chemical reaction-

Balance Chemical Reaction

HCl + MgCO3 titration

Since MgCO3 is insoluble in water, back titration is performed.


Beaker, volumetric flask, conical flask, burette, titrating stand, and measuring cylinder


An acid-base indicator is used: Phenolphthalein


  • Weigh a known amount of MgCO3 in a beaker and pour the liquid HCl acid into it. The mixture is thoroughly mixed and transferred in the volumetric flask. To make up the solution up to the mark, distilled water is added.
  • From the flask, transfer 25ml of the solution to the conical flask using a measuring cylinder.
  • Add 2 to 3 drops of phenolphthalein indicator.
  • Titrate the solution against 0.1M NaOH, and continue it till the colour changes to light pink. For accurate results, repeat the procedure three times and note down the titration reading.
  • Using N1V1=N2V2, concentration of MgCO3 is determined.

HCl + MgCO3 net ionic equation

  • Mg2+(aq) +CO32− (aq)+2H+(aq) +2Cl(aq) →Mg2+(aq) +2Cl(aq)+H2O(ℓ)+CO2(g)
  • Step2: Cancel out the elements whose ions remain unchanged throughout the reaction
  • Mg2+(aq) +CO32− (aq)+2H+(aq) +2Cl(aq) →Mg2+(aq) +2Cl(aq)+H2O(ℓ)+CO2(g)
  • Step3: The reaming equation is the net ionic equation
  • CO32− (aq)+2H+(aq)→ H2O(ℓ)+CO2(g)

HCl + MgCO3 conjugate pairs

In conjugate acid-base pairs, there is always a chemical difference of one proton between them,

  • For HCl, Cl is the conjugate base.
  • For MgCO3, CO3 is the conjugate base.
  • For H2O, OH is the conjugate base.

HCl and MgCO3 intermolecular forces

HCl is a covalent compound, and London dispersion forces and dipole-dipole interaction takes place. MgCO3 being an ionic compound, possess an electrostatic force of attraction.

HCl + MgCO3 reaction enthalpy

Reaction enthalpy of HCl reacting with MgCO3, is -50.4KJ/mol, calculated as follow:

  • Step 1: Write down the enthalpy of each element present in the reactant side and product side as tabulated below
  • Step 2: The change in enthalpy of the reaction is calculated as follows-
CompoundsEnthalpy (KJ/mol)
MgCO3 (s)-1095.79
HCL (aq)-167.15
MgCl2 (aq)-801.15
CO2 (g)-393.51
H2O (l)-285.83
Enthalpies of each element present in the reactant side and product side
  • Change in Enthalpy = (summation of enthalpies in product side) – (summation of enthalpies in reactant side)
  • Enthalpy Change = [1*(-801.15) + 1*(-285.83) + 1*(-393.51)] – [2*(-167.15) + 1*(-1095.79)] = -50.7 KJ/mol.

Is HCl + MgCO3 a buffer solution?

HCl+ MgCO3 reaction is not a buffer solution due to the presence of the strong acid that is HCl.

Is HCl + MgCO3 a complete reaction?

HCl+ MgCO3 is a complete reaction since at equilibrium complete moles of reactant are consumed, producing the complete product

Is HCl + MgCO3 an exothermic or endothermic reaction?

HCl+ MgCO3 is an exothermic reaction, since the reaction enthalpy is -50.4KJ/mol, which is negative, thereby increasing the temperature.

Is HCl + MgCO3 a redox reaction?

The HCl+ MgCO3 reaction cannot be classified as a redox reaction, because there is no electron transfer taking place, that is the oxidation state of elements on the product side remains unchanged.

Is HCl + MgCO3 a precipitation reaction?

The HCl+ MgCO3 reaction is not a precipitate reaction, since the reaction yields, MgCO3 which is a salt soluble in water; CO2 which is a gas; and H2O, so there is no precipitate formed in the reaction.

MgCO3 + 2HCl → MgCl2 + CO2 + H2O

Is HCl + MgCO3 reversible or irreversible reaction?

HCl+ MgCO3 is an irreversible reaction, due to the formation of a gas molecule on the product side, which increases entropy, which makes the product side more stable than the reactant side.

Is HCl + MgCO3 displacement reaction?

HCl+ MgCO3 is a double displacement reaction. The reaction of HCl and MgCO3 results in the formation of entirely two different compounds by interchanging the anions and cations of the reactant side.

How to balance HCl + CaCO3 + MgCO3 = CO2 + CaCl2 + Mg(OH)2?

  • First, write the unbalanced equation –
  • HCl + CaCO3 + MgCO3 = CO2 + CaCl2 + Mg(OH)2
  • Tabulate the number of moles of each element in the reactant and product side as follow:
CompoundsReactant SideProduct Side
Enthalpies of each element present in the reactant side and product side
  • To balance the equation, multiply 2 with HCl on the reactant side and multiply 2 with CO2 on the product side, which balances the reaction.
  • Therefore, the balanced equation is –
  • 2HCl + CaCO3 + MgCO3 = 2CO2 + CaCl2 + Mg(OH)2


The reaction of HCl with MgCO3 forms whitish magnesium chloride which has a variety of uses. It is used in fire extinguishers, disinfectants, flocculating agent etc. It is a double displacement, neutralization, exothermic reaction with -50.7 KJ/mol enthalpy change.

Pratham Shah

Hi....I am Pratham Manish Shah, Pursuing an Integrated MTech degree in Chemical Engineering from the Institute of Chemical Technology Mumbai Marathwada Jalna. With Lamdageeks, I am Interested in learning ongoing education opportunities to maintain knowledge of emerging technologies and methods. Let's connect via LinkedIn: www.linkedin.com/in/pratham-shah-07

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