15 Facts on HCl + H3PO4: With Several Elements Reaction

Every chemical reaction works, with chemistry and properties associated with them, whereas the reaction between two acids is explained below. Let us discuss the given reaction.

When phosphoric acid, a weak acid, reacts with HCl, categorized as a strong acid, a water-soluble chlorinated compound will be produced. H₃PO₄ has a tetrahedral arrangement and is a non-volatile, transparent, orderless liquid with a monoclinic crystalline structure.

Here we will learn more about the reaction’s mechanism, such as enthalpy, redox reaction, intermolecular force, conjugate pairs, etc., in the following article.

What is the product of HCl and H₃PO₄

Phosphorous pentachloride as a major and water as a minor product will be formed during the reaction between hydrochloric acid and phosphoric acid.

What type of reaction is HCl + H₃PO₄

The mentioned reaction is considered to be a double displacement reaction, where anion (phosphate) of phosphoric acid switches its places with cation (chlorin), leading to the formation of a completely different compound. Additionally, this type of reaction also comes under the redox reaction category.

How to balance HCl + H₃PO₄

The reaction is balanced using the following steps.

HCl+H₃PO₄ =PCl₅ + H₂O

• Step 1-Coefficient of individual chemical molecules are labeled as,
• HCl= a, H₃PO₄ = b, PCl₅ =c and H₂O=d
• Step 2- Now, we count the number of hydrogen (H), Phosphorous (P), oxygen (O), and chlorine (Cl) on both the reactant and product sides. That gives,
• On the reactant side, P=1, Cl= 1, H=4 (3 from phosphoric acid and one from hydrochloric acid), and O=4.
• On product side; P=1, Cl= 5, H=2 and O=1
• Step 3- Now equate the number of elements from both the reactant and product sides in the case of Cl.
• In the case of Cl, there is only 1 Cl on the reactant side (present in HCl). However, there are 5 Cl present on the product side (PCl₅).
• Multiplying ‘a’ with 5 results in 5 Cl on both sides, though it increased the number of H (from 4 to 8).
• Step 4- Balancing further reaction; H needs to be balanced in this case.
• d is multiplied by 4 to make the count of H equal on both sides.
• But if d=4, it automatically increases the number of O in the water.  So, the new coefficients are a=5, b=1, c=1, and d=4.
• The overall balanced equation is
• 5HCl+H₃PO₄ = PCl₅ + 4H₂O

HCl + H₃PO₄ titration

The conductometer titration can be performed using hydrochloric acid vs. phosphoric acid to observe the equivalence point of the reaction. By using the below-mentioned experiment and condition, titration between HCl and H₃PO₄ can be performed.

Apparatus used

50 ml Burette, burette holder, 10 ml pipette, conical flask, volumetric flask, and two beakers.

Indicator

During conductometry titration, no indicator will be used as the conductometer is detected by measuring the conductivity of the solution.

Procedure

• Initially, the burette is washed, rinsed, and filled with HCl, and noted the initial reading.
• The conical flask is filled with phosphoric acid, followed by adding HCl dropwise into the phosphoric acid.
• This causes the H⁺ ion to be released into the solution, but due to the presence the OH^– present in phosphoric acid, the solution will give a neutral charge till the point of equivalency.
• At the endpoint, there will be an increase in the concentration of the H⁺ ion, which will result in conducting solution and be measured by a conductor meter.

HCl + H₃PO₄ net ionic equation

The net ionic equation of the reaction scheme is.

H⁺ (aq) + Cl^– (aq) + PO₃^2- = [PCl₄⁺] [PCl₆^–] + H⁺+ OH^–

• Here HCl will be ionized into a proton (H^–) and chloride ion (Cl^–).
• While H₃PO₄ is tribasic acid which gets ionized into a hydroxide ion (OH^–) and in phosphite ion (PO₃²-). 

HCl + H₃PO₄ conjugate pairs

[H₄PO₄]⁺ will act as a conjugate base, and Cl- will be considered a conjugate acid during the reaction.

HCl+H₃PO₄ =Cl^‑ + [H₄PO₄]

HCl and H₃PO₄ intermolecular forces

• Dipole-dipole forces and London dispersion forces are present in HCl.

• Hydrogen bonds hold phosphoric acid together.

HCl + H₃PO₄ reaction enthalpy

The reaction HCl+H₃PO₄ suggests ΣΔH°_f(R) (1342.1) > ΣΔH°_f(P) (1002.1), lowering of the reaction enthalpy where the energy of the reaction is higher than the energy of the product.

Is HCl + H₃PO₄ a buffer solution

This reaction mixture will not yield a buffer solution. The similar nature of the reagents, weak acid H3PO4, and strong acid HCl, can yield buffer solution only at a specific concentration.

Is HCl + H₃PO₄ a complete reaction

The reaction mentioned above is not complete as there is no product on the right side of the above reaction, and for a reaction to be complete, there must be one or more products, such as phosphorous pentachloride or water.

Is HCl + H₃PO₄ an exothermic or endothermic reaction

The reaction between hydrochloric acid and phosphoric acid is considered an exothermic reaction where the reaction of both element will release heat.

Is HCl + H₃PO₄ a redox reaction

The reaction between hydrochloric acid and phosphoric acid is not a redox reaction because as no change in oxidation state is observed.

Is HCl + H₃PO₄ a precipitation reaction

The reaction mentioned above is not a precipitation reaction since the product yellow coloured phosphorous pentachloride is soluble in the other by-product, which is water.

Is HCl + H₃PO₄ reversible or irreversible reaction

The mentioned reaction is reversible as the equilibrium can be shifted backward by lowering the concentration of water. In addition, the intermediate form is exceptionally reactive in its natural state and can change the direction in which a reaction is proceeding by applying more force.

Is HCl + H₃PO₄ displacement reaction

The reaction between the compound is not a displacement reaction, as one element from both compounds get displaced to yield the final product.

Conclusion

The double displacement reaction between HCl, which is a strong acid, and phosphoric acid, which is a weak acid, resulted in the formation of yellow-colored water consisting of phosphorous pentachloride, along with the evolution of heat and is considered to be a reversible reaction according to Le Chatelier’s principle.