Hydrogen iodide and Sulphur dioxide are both inorganic compounds abbreviated with the chemical formula HI and SO2 , respectively. Let us explore the reaction between HI and SO2.
HI or Hydroiodic acid is a water-soluble colorless gas. It is used in organic chemistry to synthesize alkyl iodide from primary ethanol. SO2 is a gas with a burnt odor that can be smelled of burning matchsticks.
In this article, we are going to be aware of how HI reacts with SO2. Besides, it will highlight the product, reaction type, ionic equation, etc.
What is the product of HI and SO2?
Iodine (I2), Sulphur (S) and Water (H2O) are the three product formed in the reaction between Hydrogen iodide (HI) and Sulphur dioxide (SO2).
HI + SO2 ——> I2+ S + H2O
What type of reaction is HI + SO2
The reaction between Hydrogen iodide (HI) with Sulphur dioxide (SO2) is called an oxidation-reduction reaction because SO2 acts as an oxidizing agent and HI acts as a reducing agent.
How to balance HI + SO2
To balance HI + SO2 reaction, the algebraic method is followed.
- HI + SO2 —–> I2 + S + H2O is an unbalanced general equation.
- Algebraic variables will be added to each element (as stoichiometric co-efficient) on both the product and reactant sides.
- aHI + bSO2 —–> cI2 + dS + eH2O
- The similar types of elements are arranged together and the coefficients are added until the equation is balanced.
- After final rearrangements, we get the following:
| Elements | Equation for elements |
|---|---|
| H | a = 2e |
| I | a = 2c |
| S | b = d |
| O | H |
- Simplifying all using the Gaussian elimination method, the final equation is written as-
- We get, a = 2c = 2e = 4b = 4d
- If a = 4, then c = 2, e = 2, b = 1 & d = 1
- Therefore, the balanced equation is as follows:
- 4 HI + SO2 = 2I2 + S + 2H2O
HI + SO2 titration
The mixture HI + SO2 does not participate in the titration reaction because both compounds possess acidic nature.
HI + SO2 net ionic equation
- The reaction HI + SO2 gives the following net equation:
S4+ + 4I– ——> S + 2I2
- The reaction undergoes the following mechanisms:
- At first, Hydrogen iodide (HI) dissociates to produce a Hydrogen ion (H+) and an iodine ion (I–) in the following way-
HI —-> H+ + I–
- Similarly, the SO2 compound dissociates in the sulfur ion (S4+) and oxide ion (O2-). The equation is as follows:
SO2 —-> S4+ + 2O2-
- Now, the sulfur ion oxidizes the iodide ion (I) from I (-I) to I (0).
Equation 1: I– – e– —–> I0 (Oxidation)
- In the same way, sulfur ion reduces from S (IV) ion to S (0) ion.
Equation 2: S4+ + 4e– —–> S0 (Reduction)
- In order to balance the number of electrons for both the oxidation and reduction process, the equation- 1 will be multiplied by 4.
Therefore, 4I– – 4e– —-> 4I0
- After canceling the electron, the net equation for the oxidation-reduction reaction will be as follow:
S4+ + 4I– ——> S + 4I
HI + SO2 conjugate pairs
The reaction HI + SO2 consists of following conjugate pair,
- The conjugate pair of strong acid, HI = I– (Iodine ion)
- The conjugate base of SO2 = HSO3– (bisulfite ion)
HI and SO2 intermolecular forces
The HI + SO2 reaction exhibits the following intermolecular forces:
- HI molecules show Dipole-dipole forces due to the presence of polar H & I
- HI shows low polarity London dispersion forces
- SO2 only exhibits dipole-dipole interaction.
HI + SO2 reaction enthalpy
The reaction enthalpy of HI + SO2 is -207.686 KJ/ mol. The enthalpy is derived as follows-
| Reactants/ Products | Enthalpy of formation |
|---|---|
| HI | -26.466 KJ/ mol |
| SO2 | -296.9 KJ/ mol |
| I2 | -62.5 KJ/ mol |
| S | -1.85 KJ/ mol |
| H2O | -241.8 KJ/ mol |
4 HI + SO2 = 2I2 + S + 2H2O
- ΣΔH⁰f(reactants) = [4 * -26.466 + (-296.9)}] = -402.764 KJ/ mol
- ΣΔH⁰f(products) = [(2 * -62.5) + (-1.85) + (2 * -241.8)] = -610.45 KJ/ mol
- As, ΔH⁰f(reaction) = ΣΔH⁰f(products) – ΣΔH⁰f(reactants)
- ΔH⁰f(reaction) = -207.686 KJ/ mol
Is HI + SO2 a buffer solution
The mixture of HI + SO2 is not a buffer solution because both HI and SO2 are acids and no conjugate pairs produce in the mixture.
Is HI + SO2 a complete reaction
The reaction HI + SO2 is a complete reaction because it produces stable compounds like iodine and sulfur.
Is HI + SO2 an exothermic or endothermic reaction
The HI + SO2 reaction is exothermic because the energy produced after bond formation is higher than the energy absorbed at the initial bond dissociation (ΣΔH⁰f(reactants) > ΣΔH⁰f(products)).
Is HI + SO2 a redox reaction
The reaction between HI + SO2 is a redox reaction because SO2 acts as an oxidizing agent and HI acts as a reducing agent.
Is HI + SO2 a precipitation reaction
The reaction between HI & SO2 is a precipitation reaction because the product, S is insoluble in water.
Is HI + SO2 reversible or irreversible reaction
The HI + SO2 reaction is an irreversible redox reaction because the spontaneous release or acceptance of electrons occurs in one way.
Is HI + SO2 displacement reaction
The reaction HI + SO2 is not a displacement reaction because sulfur and iodine get reduced and oxidized respectively causing no interchange in their position.
Conclusion
The reaction between Hydroiodic acid and Sulphur dioxide exhibits two important compounds. Iodine is a lustrous black solid readily used in chemical analysis. Besides, sulfur, a yellow solid, acts as an excellent fungicide, pesticide, and fertilizer.
Hello….I am Prity Banerjee, a graduate in Chemistry. I am currently invested in the field of Science and Technology. My interest lies in the latest technology and discoveries in the field of pharmaceutical science and chemistry. I am currently working as a Subject Matter Expert. Apart from the professional front, I love singing, dancing and spending time with my pets. Lets connect over LinkedIn:
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