11 Facts on HCl +Hg2O : What, How to Balance & FAQs

Hydrochloric acid and Mercurous oxide are two of the many inorganic compounds. Let us explore what happens when we make them react to each other.

The aqueous solution of hydrogen chloride is an inorganic acid known as HCl, sometimes known as muriatic acid.Hg2O, also known as mercurous oxide, is an inorganic metal oxide. These two when react together form a toxic compound.

Let us in this article dive more into the facts, and properties like chemical nature, the product formed , conjugate pairs, and equations associated with this reaction.

What is the product of HCl and Hg2O?

When HCl reacts with Hg2O it forms Hg2Cl2 as the product, also known as mineral calomel. The reaction scheme is as follows :

Reaction scheme of Hg2Cl2 formation

What type of reaction is HCl + Hg2O?

The reaction between HCl and Hg2O is a displacement reaction.

How to balance HCl + Hg2O?

Step 1- Labeling of atoms.

Each individual molecule is labeled as A, B, C, and D as four atoms are present.HCl+Hg2O = Hg2Cl2 + H2O reaction is not balanced. If we go by this reaction number of molecules on LHS is not equal to number of molecules on RHS.

A Hg2O+B HCl = C Hg2Cl2 + D H2O

Step 2 – Now we check the coefficients for each atom for the reactants and products.

  • Hg 2A=2C
  • O – 1A=1D
  • H – 1B=2D
  • Cl – 1B=2C

Step 3- The variables and coefficients are further balanced and calculated as follows-

A = 1, B = 2, C = 2, and D =1

So, the overall balanced equation will be, Hg2O + 2HCl → Hg2Cl2 + H2O

HCl + Hg2O net ionic equation

The net ionic equation of HCl+Hg2O is – Hg2O + 2HCl → 2Hg++2Cl + H2O

HCl+ Hg2O conjugate pairs?

  • The conjugate base pair of HCl = Cl, Chloride ion.
  • The conjugate pair for Hg2O = Hg+

HCl and Hg2O intermolecular forces?

HCl and Hg2O both of them show ionic intermolecular interactions. We observe dipole-dipole interaction in HCl whereas in Hg2O it is electrostatic interactions and that too of low polarization.Hg2O is insoluble in water but soluble in nitric acid.

Is HCl + Hg2O a complete reaction?

The reaction HCl+Hg2O is a complete reaction as a complete product Hg2Cl2 is formed following the reaction as given below.

Hg2O + 2HCl → Hg2Cl2 + H2O

Is HCl + Hg2O an exothermic or endothermic reaction?

The reaction HCl+Hg2O is an exothermic reaction, it is concluded from the following facts-

  • The product Hg2Cl2 formed from the reaction of HCl and Hg2O is stable as compared to that of the reactant Hg2O.
  • Also, since it is a double displacement reaction.

Is HCl + Hg2O a redox reaction?

The reaction HCl+Hg2O is a double displacement/metathesis reaction thus it is NOT a redox reaction.

Is HCl + Hg2O a precipitation reaction?

The reaction HCl+Hg2O is not a precipitation reaction as the product formed, Hg2Cl2 , is soluble in water.

Is HCl + Hg2O reversible or irreversible reaction?

HCl+Hg2O is an irreversible reaction as the Hg2Cl2 product formed is stable as opposed to the reactant Hg2O which is chemically unstable.

Is HCl + Hg2O displacement reaction?

The reaction between HCl and Hg2O is a double displacement reaction or metathesis reaction.


The reaction between HCl and Hg2O forms a product, Hg2Cl2, which is an example of a mercury (I) compound. Calomel or Hg2Cl2 appears as an odorless and white solid in nature. It plays an extremely important role in electrochemistry and is used as a component in reference electrodes.

Shubhi Mishra

Hello..... I am Shubhi Mishra. I share an eternal love for Chemistry. It is never "too much" to learn and think about Chemistry. My qualifications stand as MSc-Chemistry, BSc-BEd(Physical Sciences). Let's connect through my LinkedIn profile-https://www.linkedin.com/in/shubhi-m-a310191b8/

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