3 Facts on Cr2O3 + HCl: What, How To Balance

In this article, “cr2o3 + hcl”, the product of this reaction, balancing method and the type of reaction is discussed briefly.

Cr2O3 or chromium oxide is a green coloured crystalline compound with molecular mass 151.99 g/mol. On the other side HCl is a strong mineral acid with molecular weight 36.458g/mol. In their chemical reaction chromium chloride (CrCl3) and water (H2O) is obtained as product.

Let’s focus on the following discussions on the reaction.

What is Cr2O3 + HCl?

Chromium oxide or chromia is a crystalline solid compound which is basically used as pigment. The appearance of this compound is light to dark green with melting and boiling point 24350 C and 40000C respectively. It is a water insoluble compound.

The packing of the crystal is hexagonal close packing (HCP) with corundum structure. It is a hard and brittle material. Cr2O3 or chromia can be synthesized from sodium di chromate (Na2Cr2O7) reduction.

Na2Cr2O7 + S → Na2SO4 + Cr2O3.

It can be also synthesized by the decomposition of chromium salt or by the exothermic decomposition of ammonium dichromate.

(NH4)2Cr2O7 → Cr2O3 + N2 + H2O

cr2o3 + hcl
 Structure of Cr2O3

Hydrochloric acid or HCl also known as muriatic acid is a colorless liquid with pungent smell. It is a very strong acid with pH = 3.01. It has a large ka value (pka = -5.9).

What is the product of Cr2O3 + HCl?

HCl is made with hydrogen and a nonmetal(Cl). After reacting with chromium oxide, one salt of chromium and water is obtained. The above reaction is one type of redox reaction. In this reaction chromium chloride (CrCl3) and water (H2O) is formed.

Cr2O3 + HCl → CrCl3 + H2O

These reaction proceeds towards forward direction due to increase of entropy (disorder) in a higher extent. Because water is formed in product side which is a highly stable covalent compound.

Chromium chloride is a chromium compound in which chromium presents in +3 oxidation state. The molecular weight of this compound is 158.36 g/mol. The appearance of the anhydrous chromium chloride is a violet coloured solid and it is water soluble but insoluble in ethanol, ether, acetone. It is used as catalysts and precursors to dyes for wool.

How to balance Cr2O3 + HCl?

Balancing of chemical equation is mandatory to determine how many numbers of molecules or moles are required to complete a chemical reaction. There are some steps which should be followed to balance any chemical reaction. They are-

  • At first, the unbalanced equation is written
  • Then balance the equation by using proper method.
  • Physical state of the each of the reactant and product is written within bracket.

Now, it’s time to balance the above reaction through the following method.

  1. Writing up the unbalanced equation-

Cr2O3 + HCl → CrCl3 + H2O

2. Calculation of required number of molecules and add them as the stoichiometry before each of the reactant and product.

In reactant side, two chromium and three oxygen molecules are present in Cr2O3 molecule. To balance the number of chromium (Cr) and oxygen (O), 2 and 3 will be multiplied with CrCl3 and H2O respectively in product side. Similarly, to balance the number of chlorine and oxygen, 6 will be multiplied with HCl.

After multiplying these numbers as stoichiometry the final balance chemical equation will be-

Cr2O3 + 6HCl → 2CrCl3 + 3H2O

What type of reaction is Cr2O3 + HCl?

The above reaction is an example of redox reaction. Redox reactions are basically the combination of two reactions. They are-

  1. Oxidation reaction
  2. Reduction reaction

In this redox reaction one reactant is reduced and another reactant is oxidized by each other to form the oxidized and reduced product respectively.

Now coming to this reaction-

Cr2O3 + 6HCl → 2CrCl3 + 3H2O

In this reaction, Cr2O3 is reduced to form CrCl3 and HCl is oxidized to H2O. Thus, HCl is playing a role of reducing agent and Cr2O3 is playing a role of oxidizing agent in this reaction.

So, it is definitely a redox reaction in which reduction and oxidation take place simultaneously in the same reaction.

Redox Reaction


From the above article we have collected the information on the reaction of Cr2O3 with HCl. The products obtained from the redox reaction are chromium chloride (Cr2O3) and water (H2O).

Aditi Roy

Hi..I am Aditi Roy, I have completed my graduation from University of Calcutta and am pursuing M.Sc in Chemistry from Techno India University. My area of specialization is on Inorganic Chemistry.

Recent Posts