The Chemistry Behind HCl + Ag2CrO4: 15 Facts You Should Know

HCl is a strong acid and it can easily react with basic salt silver chromate without any catalyst. Let us discuss the chemistry behind this reaction.

Ag₂CrO₄ or silver chromate is mainly used for the mohr’s salt titration in analytical chemistry. It is a metallic salt and reacts with water to form a base so it is a basic salt and reacts with a diluted or concentrated form of acid. HCl or hydrochloric acid is a strong mineral acid that easily donates a proton.

Although there will be some parameters and limitations present in this reaction. Now we can discuss more the mechanism of the reaction like enthalpy, redox reaction, intermolecular force, conjugate pairs, etc with an explanation in the following part of the article.

1. What is the product of HCl and Ag₂CrO₄?

H₂CrO₄ (Chromic acid) and AgCl (silver chloride) are formed when diluted HCl and Ag₂CrO₄ are reacted together but when we use conc. HCl and Ag₂CrO₄ then dichromic acid (H₂CrO₇) and water are also formed along with silver chloride.

HCl(dil.) + Ag₂CrO₄ = AgCl + H₂CrO₄

HCl(Conc.) + Ag₂CrO₄ = H₂CrO₇ + AgCl + H₂O

2. What type of reaction is HCl + Ag₂CrO₄?

HCl + Ag₂CrO₄ reaction is an example of a double displacement reaction, and a redox and precipitation reaction. It is also a hydrolysis reaction because, in the course of the reaction, water is formed.

3. How to balance HCl + Ag2CrO4?

HCl + Ag₂CrO₄ = H₂CrO₇ + AgCl + H₂O, we have to balance the equation in the following way-

• First, we label all the reactants and products by A, B, C, D, and E as there are five different molecules obtained for this reaction and the reaction looks like this,
• A HCl + B Ag₂CrO₄ = C H₂CrO₇ + D AgCl + E H₂O
• Equating the coefficients for the same type of elements by rearranging them.
• After the rearrangement of coefficients of the same elements by their stoichiometric proportion, we get,
• H = A = 2C = 2E, Cl = A = D, O = 4B = 7C = E, Ag = 2B = D, Cr = B = C.
• Using the Gaussian elimination and equating all the equations we get, A = 4, B = 2, C = 1, D =4, and E = 1
• The overall balanced equation will be,
• 4HCl + 2Ag₂CrO₄ = H₂CrO₇ +4 AgCl + H₂O
• And another balanced equation will be, Ag₂CrO₄ + 2HCl = H₂CrO₄ + 2AgCl

4. HCl + Ag₂CrO₄ titration

To estimate the quantity of chromate or acid strength, we can titrate Ag₂CrO₄ and HCl_.

Apparatus used

We need a burette, conical flask, burette holder, volumetric flask, and beakers for this titration.

Titre and titrant

HCL versus Ag₂CrO₄, HCl acts as a titrant taken in the burette and the molecule to be analyzed is Ag₂CrO₄ taken in a conical flask.

Indicator

The whole titration is done in an acidic medium or acidic pH so the best suitable indicator will be phenolphthalein which gives perfect results for this titration at given pH.

Procedure

The burette is filled with standardized HCl. Ag₂CrO₄ is taken in a conical flask along with respective indicators. HCl is added dropwise to the conical flask and the flask is shaken constantly. After a certain time, when the endpoint arrives, the indicator changes its color and the reaction is done.

5. HCl+ Ag₂CrO₄ net ionic equation

The net ionic equation between HCl + Ag₂CrO₄ is as follows,

H⁺(aq.) + Cl^–(aq.) + Ag⁺(aq.) + CrO₄^2-(aq.) = 2H⁺(aq.) + CrO₇^2-(aq.) + H⁺(aq.) + OH^–(aq.) + Ag⁺(aq.) + Cl^–(aq.)

• HCl will be ionized as proton and chloride as it is strong acid and electrolyte.
• After that Ag₂CrO₄ also dissociates into Ag⁺ ion and CrO₄^2-ion as it is also a strong electrolyte
• In the product part, AgCl is ionized into Ag⁺ and Cl^–as it is a strong electrolyte and salt in the aqueous form.
• H₂O ionized into proton and hydroxide ion.
• H₂CrO₇ is also ionized into di protonic form and CrO₇^2- as counter ion as it is an acidic molecule and can be dissociated into an aqueous medium.

6. HCl+ Ag₂CrO₄ conjugate pairs

In the reaction, HCl+ Ag₂CrO₄ conjugate pairs will be the corresponding de-protonated and protonated form of that particular species which are listed below-

• Conjugate pair of HCl = Cl^–
• Conjugate pair of OH^– = H₂O
• Conjugate part of CrO₇^2- = HCrO₇^–
• Conjugate part of HCrO₇^– = H₂CrO₇
• Conjugate part of H₂CrO₄ = CrO₄^2-

7. HCl and Ag₂CrO₄ intermolecular forces

 HCl + Ag₂CrO₄ has the following intermolecular reactions,

Molecule	Acting force
HCl	Electrostatic, van der waal’s Dipole interaction
Ag2CrO4	Strong electrostatic force and ionic interaction, Coulumbic force, metallic bond
AgCl	Electrostatic force, ionic interaction,
H2CrO4 / H2CrO7	Covalent force, ionic interaction, dipole interaction
H2O	Ionic interaction and H-bonding

8. HCl + Ag2CrO4 reaction enthalpy

HCl + Ag₂CrO₄ reaction enthalpy is +1001.24 KJ/mol which can be obtained by the formula: enthalpy of products – enthalpy of reactants. Here the change in enthalpy is positive.

Molecule	Enthalpy (KJ/mol)
Ag2CrO4	-731.8
HCl	-36.45
AgCl	-127.01
H2CrO7	-2033
H2O	-68

9. Is HCl + Ag₂CrO₄ a buffer solution?

In the reaction between HCl + Ag₂CrO_4, there is no such buffer formed but the mixture of H₂CrO₇ can control the pH even added base in the solution.

10. Is HCl + Ag₂CrO₄ a complete reaction?

The reaction between HCl + Ag₂CrO₄ is complete because it gives two major ones: an electrolytic salt and an acidic molecule along with water as a by-product.

11. Is HCl + Ag₂CrO₄ an exothermic or endothermic reaction?

The reaction of HCl + Ag₂CrO₄ is endothermic in terms of thermodynamics first law. This reaction released more energy and temperature to the surroundings, where δH is always positive.

12. Is HCl + Ag₂CrO₄ a redox reaction?

HCl + Ag₂CrO₄ reaction is a redox reaction because in this reaction chromium gets reduced and also silver gets oxidized. Where HCl acts as a reducing agent and Ag₂CrO₄ acts as an oxidizing agent.

13. Is HCl + Ag₂CrO₄ a precipitation reaction

The reaction between HCl + Ag₂CrO₄ is a precipitation reaction because AgCl gets precipitated in the solution at certain pH.

14. Is HCl + Ag₂CrO₄ reversible or irreversible reaction?

The reaction between HCl+ Ag₂CrO₄ is irreversible because it produces an acid molecule. Due to the production of the acidic molecule, the equilibrium shifts towards the right-hand side only or forward directions.

HCl + Ag₂CrO₄ —-> AgCl+ H₂CrO₇ + H₂O

15. Is HCl + Ag₂CrO₄ displacement reaction?

The reaction between HCl+ Ag₂CrO₄ is an example of a double displacement reaction. Because in the above reaction, H⁺ was displaced by Ag⁺ from HCl, and Ag⁺ was displaced by proton from the Ag₂CrO₄.

Conclusion

The reaction between HCl and Ag₂CrO₄ is important because it can produce dichromic acid. In the course of reaction silver chloride is also produced so it is an industrially important reaction for the production of AgCl and H₂CrO₇. When we use diluted HCl acid then it forms H₂CrO₄.