Hydrochloric acid and sulphur(VI) oxide show redox reactions. In this article, we will understand some interesting facts about the reaction.
Chemically SO3 is called sulfuric oxide or sulfuric anhydride. It is used for the production of H2SO4 and explosives. HCl is a strong inorganic acid. The mixture of HCl and SO3 acts as an oxidation-reduction reaction. Oxidation occurs when the oxidation state increase and vice versa. In this reaction, SO3 acts as an oxidizing agent, and HCl acts as a reducing agent.
Let us discuss how to balance redox reaction between HCl and SO3, the products formed in this reaction, net ionic equation, conjugate pairs and many other related facts in this article.
What is the product of HCl and SO3?
The products formed by the reaction between SO3 and HCl are sulphur dioxide (SO2), Chlorine gas (Cl2) and water (H2O). The chemical equation can be written as follows:
SO3(l) + HCl(aq) = SO2(aq) + Cl2(g) + H2O(l)
What type of reaction is HCl + SO3?
The mixture of HCl + SO3 follows the oxidation-reduction (redox) reaction in which both oxidation and reduction occur simultaneously. In this reaction, sulphur trioxide acts as an oxidizing agent, and hydrochloric acid acts as a reducing agent.
How to balance HCl + SO3?
Follow the steps given below to balance the reaction between HCl and SO3.
- Initially, designate each reactant and product with the symbol and their state.
SO3(l) + HCl(aq) = SO2(aq) + Cl2(g) + H2O(l)
- Count different types of atoms in reactant and product and fill the table.
| Atom type | Reactant | Product |
|---|---|---|
| S | 1 | 1 |
| O | 3 | 3 |
| H | 1 | 2 |
| Cl | 1 | 2 |
- As the number of hydrogen and chlorine atoms is not the same, multiply HCl by 2. Then again, check the number of atoms.
SO3(l) + 2HCl(aq) = SO2(aq) + Cl2(g) + H2O(l)
| Atom type | Reactant | Product |
|---|---|---|
| S | 1 | 1 |
| O | 3 | 3 |
| H | 2 | 2 |
| Cl | 2 | 2 |
- Finally, we get a balanced chemical equation in which the stoichiometry for HCl, SO3, SO2, Cl2, and H2O comes out to be 2, 1, 1, 1, 1 respectively.
HCl + SO3 titration
For the mixture of HCl and SO3, redox titration is used.
Indicator:
Potassium permanganate (acts as self-indicator), phenolphthalein
Apparatus:
Funnel, Conical flask, Burette stand, Burette, Pipette, Stirrer, White glazed tile, Potassium permanganate, Hydrochloric acid, Sulphuroxide
Procedure:
- Initially, the HCl and SO3 should be standardized with KMnO4, acting as a self-indicator.
- Rinse the burette with M/10 KMnO4 solution and note the initial reading.
- Take 10 ml of HCl solution with the help of a pipette and transfer it to a conical flask.
- Dropwise, add KMnO4 solution till permanent pink colour appears.
- Note the final reading and determine the concentration of HCl.
- Then wash, rinse the burette with HCl and titrate with SO3.
- Add a few drops of phenolphthalein which acts as an indicator.
- Dropwise, add HCl solution into the SO3 solution till you get the pink colour.
- Write the final reading of the burette and determine the concentration of SO3.
HCl + SO3 net ionic equation
The ionic equation for HCl + SO3 is: SO3(l) + 2H+(aq) + 2Cl–(aq) = SO2(aq) + Cl2(g) + H2O(l)
The following steps should be followed:
- Initially, write the balanced chemical equation in terms of their physical state.
SO3(l) + 2HCl(aq) = SO2(aq) + Cl2(g) + H2O(l)
- The molecules in pure substances like SO3, SO2, Cl2, and H2O do not dissociate into ions, but HCl is a strong acid that dissociates into proton (H+) and chloride (Cl-) ions.
SO3(l) + 2H+(aq) + 2Cl–(aq) = SO2(aq) + Cl2(g) + H2O(l)
HCl + SO3 conjugate pairs
The mixture of HCl and SO3 does not form conjugate pairs. As observed from the ionic equation, both HCl and SO3 do not give or accept a proton (H+). Therefore, the mixture cannot be considered as conjugate pairs.
HCl and SO3 intermolecular forces
HCl and SO3 show the dipole-dipole intermolecular force of attraction. Due to the electronegativity difference between H and Cl, the HCl molecule shows permanent dipole moments. Also, the net dipole moment is not zero due to trigonal planar geometry.
HCl + SO3 reaction enthalpy
The standard enthalpy of the reaction between HCl and SO3 is -2.3 kJmol-1. The standard enthalpy of the reaction can be calculated using the value listed in Table.
| S.No. | Chemical Compound | Standard enthalpy of formation (Hform) (kJmol-1) |
|---|---|---|
| 1 | HCl | -92.3 |
| 2 | SO3 | -395.7 |
| 3 | SO2 | -296.8 |
| 4 | Cl2 | 0.0 |
| 5 | H2O | -285.8 |
Hform = HSO2 + HCl2 + HH2O – HHCl – HSO3
= (-296.8-285.8-o.0+2*92.5+395.7)
= -2.3 kJmol-1
Is HCl + SO3 a buffer solution?
A mixture of HCl + SO3 does not form a buffer solution because a buffer solution is formed by weak acid or weak base with the salt of a weak acid strong base.
Is HCl + SO3 a complete reaction?
The mixture of HCl and SO3 is a complete reaction because SO3 acts as an oxidizing agent which oxidizes chloride to chlorine gas.
Is HCl + SO3 an exothermic or endothermic reaction?
The chemical reaction between HCl and SO3 is exothermic. The calculated standard enthalpy of the reaction of HCl and SO3 comes out to be negative.
Is HCl + SO3 a redox reaction?
The chemical reaction between HCl and SO3 is a redox reaction because the oxidation state of the sulphur atom decreases from +6 to +4, and the oxidation state of the chlorine atom increases from -1 to zero. In this reaction, both oxidation-reduction occur simultaneously.
SO3(l) + 2H+(aq) + 2Cl–(aq) = SO2(aq) + Cl2(g) + H2O(l)
Is HCl + SO3 a precipitation reaction?
The reaction between HCl and SO3 is not a precipitation reaction. All the molecules present in the reaction mixture are either in aqueous, liquid and gaseous states.
Is HCl + SO3 reversible or irreversible reaction?
The reaction between HCl and SO3 is not reversible because the Cl2 gas evolved out of the reaction. According to Le Chatiler’s principle, if gases escape the reaction mixture, the reaction will proceed in the forward direction at a constant temperature and pressure.
Is HCl + SO3 displacement reaction?
The chemical reaction between HCl and SO3 is not a displacement reaction which can be observed from the balanced chemical equation.
Conclusion
The SO3 readily reacts with HCl by redox reaction in which SO3 acts as an oxidizing agent and HCl as a reducing agent. Therefore, the reaction is the simple example of redox reaction.
Hello, I am Dr. Vikas Khatri. I completed my PhD from the Department of Chemistry, Indian Institute of Technology Delhi. I have several research articles published in International Journals. I have more than 10 years of experience working as a chemistry professional. Please go through my LinkedIn profile for further details:
Hi Fellow Reader,
We're a small team at Techiescience, working hard among the big players. If you like what you see, please share our content on social media. Your support makes a big difference. Thank you!