Potassium chlorate (KClO_{3}) is a highly reactive chlorate salt, and H_{2}SO_{3} (sulfurous acid) is an inorganic sulphur oxo acid. Let us examine their reaction in detail.

**KClO _{3} is a white monoclinic crystal with a saline taste. It is a chemical oxygen generator in laboratories. As a powerful oxidizing agent, it is primarily used in fireworks. H_{2}SO_{3 }is a colorless inorganic acid, soluble in water. As a reducing agent, it is used as a bleaching agent.**

In this article, let us discuss important features of the reaction H_{2}SO_{3 }+ KClO_{3}, such as the product formed, the type of reaction, enthalpy change etc.

## What is the product of H_{2}SO_{3} and KClO_{3}?

**Potassium chloride (KCl) and sulphuric acid (****H _{2}SO_{4}**

**) are the products formed when sulphurous acid reacts with potassium chlorate.**

** 3H _{2}SO_{3} + KClO_{3} ——-> KCl + 3H_{2}SO_{4}**

## What type of reaction is H_{2}SO_{3} + KClO_{3}?

**H _{2}SO_{3}**

**+**

**KClO**

_{3}**is an oxidation-reduction (redox) type of reaction.**

## How to balance H_{2}SO_{3} + KClO_{3}?

**H _{2}SO_{3}**

**+**

**KClO**–

_{3 }is balanced using the following steps** KClO _{3 }+ 3**

**H**

_{2}SO_{3}

_{ }**= KCl + 3H**

_{2}**SO**

_{4}**To denote the unknown coefficients, assign an alphabet to each compound of the reaction.****a KClO**_{3 }+ b H_{2}SO_{3}= c KCl + d H_{2}SO_{4}**Create an equation by equating the coefficients of same type, for each element, involved in the reaction.****H → 2b=2d, S → b=c, Cl → a=c, K → a=c, O → 3a+3b=4d****Determine the values of each assigned coefficient by using the Gaussian elimination method.****The value of coefficients obtained after simplification****a=1, b=3, c=1, d=3.****Therefore, the balanced equation after substituting the values of all the coefficients is –****KClO**_{3 }+ 3H_{2}SO_{3}_{ }= KCl + 3H_{2}SO_{4}

## H_{2}SO_{3} + KClO_{3} _{ }titration

**A redox titration between H _{2}SO_{3} and KClO_{3} is carried out to determine the amount of potassium and chlorine.**

**Apparatus**

**Burette, burette holder, pipette, wash bottle, conical flask, volumetric flask, dropper and beakers.**

**Indicator**

**Phenolphthalein is used as the indicator as the titration is done in an acidic medium.**

**Procedure**

**The burette is filled with standardized H**_{2}SO_{3.}**The KClO**_{3}solution is pipetted out and transferred into the conical flask.**Add a few drops of phenolphthalein indicator.****H**_{2}SO_{3}is added drop by drop into the conical flask, and the flask is swirled constantly.**The appearance of pale pink color marks the equivalence point of the titration.****Note the burette reading and repeat the procedure for 3 concordant readings.****The quantity of potassium and chlorine is estimated by using the formula,****V**_{1}S_{1 }= V_{2}S_{2}.

## H_{2}SO_{3} + KClO_{3} _{ }net ionic equation

**The net ionic equation between H _{2}SO_{3} + KClO_{3}**

_{ }**is:**

**3H _{2}SO_{3}**

**(aq)**

**+ ClO**

_{3}^{–}

_{ }**(aq) =**

_{ }**Cl**

^{–}**(aq) + 2H**

^{+}

**(aq)**

**+ SO**

_{4}^{2-}_{ }**(aq)**

**To elucidate the net ionic equation, the following steps are followed –**

**The balanced equation along with its physical state is written first.****3H**_{2}SO_{3 }(aq) + K**ClO**_{3}_{ }**(aq)****= KCl(aq)**_{ }+**H**_{2}**SO**_{4}**(aq)****The electrolytes, which are strong, are split into their respective ions.****H**_{2}SO_{3 }is a weak electrolyte, while K**ClO**_{3, }KCl, and**H**_{2}**SO**_{4 }**are strong electrolytes in an aqueous solution. The equation now becomes,****3H**_{2}SO_{3}**(aq)****+ K**^{+}**(aq)****+ ClO**_{3}^{–}_{ }**(aq) =**_{ }**K**^{+}**(aq) +****Cl**^{–}**(aq) + 2H**^{+}(aq)**+ SO**_{4}^{2-}**(aq)****The spectator ions (****K**^{+}) are cancelled on both sides of the equation to get the**net ionic equation.****3H**_{2}SO_{3}**(aq)****+ ClO**_{3}^{–}_{ }**(aq) =**_{ }**Cl**^{–}**(aq) + 2H**^{+}**(aq)****+ SO**_{4}^{2-}_{ }**(aq)**

## H_{2}SO_{3} + KClO_{3} _{ }conjugate pairs

**Conjugate base of H**_{2}SO_{3 }as HSO_{3}^{– }**KClO**_{3}is a neutral salt, so it has no conjugate pair.

## H_{2}SO_{3} + KClO_{3} _{ }intermolecular forces

**The intermolecular forces in H**_{2}SO_{3}are London-dispersion forces, electrostatic forces and dipole-dipole interactions.**KClO**,_{3}exhibits ion-dipole interactions**since it is an ionic compound.**

## H_{2}SO_{3} + KClO_{3} _{ }reaction enthalpy

**H _{2}SO_{3} + KClO_{3} reaction enthalpy is -205.3 KJ/mol. **

**Enthalpy values of reactants and products involved in the reaction are listed below –**

Molecule | Enthalpy in KJ/mol |
---|---|

KClO_{3} | -391.2 |

H_{2}SO_{3} | -655.5 |

KCl | -438 |

H_{2}SO_{4} | -814 |

**Enthalpy values of reactants and products**

**The enthalpy of the reaction is obtained by using the formula: enthalpy of products – enthalpy of reactants.**

**∆H**_{f}^{°}(reaction) = ∆H_{f}^{°}(products) – ∆H_{f}^{°}(reactants)

**= -1252 – (-1046.7)****KJ/mol****= -205.3 KJ/mol**

## Is H_{2}SO_{3} + KClO_{3} a buffer solution?

**H _{2}SO_{3} + KClO_{3} does not form a buffer solution**,

**as KClO**

_{3 }is a neutral salt formed by the neutralization reaction of a strong acid and a strong base.## Is H_{2}SO_{3} + KClO_{3} a complete reaction?

**H _{2}SO_{3} + KClO_{3} _{ }is a complete reaction since the products are completely formed at equilibrium.**

## Is H_{2}SO_{3} + KClO_{3} an exothermic reaction?

**H _{2}SO_{3} + KClO_{3} is an exothermic reaction following thermodynamics first law. Moreover, the reaction enthalpy is found to be negative.**

## Is H_{2}SO_{3} + KClO_{3} a redox reaction?

**H _{2}SO_{3} + KClO_{3} is a redox reaction where,**

**Sulphur is oxidized from +4 to +6 oxidation state.****Chlorine is reduced from +5 to -1 oxidation state.**

## Is H_{2}SO_{3} + KClO_{3} a precipitation reaction?

**H _{2}SO_{3} + **

**KClO**

_{3}is not a precipitation reaction as the products formed are completely soluble in the reaction mixture.## Is H_{2}SO_{3} + KClO_{3} an irreversible reaction?

**H _{2}SO_{3} + **

**KClO**

_{3}is an irreversible reaction as**the products formed react with each other to form chlorine gas, so reverse reaction is not favoured.**

## Is H_{2}SO_{3} + KClO_{3} a displacement reaction?

**H _{2}SO_{3} + KClO_{3} _{ }is not a**

**displacement reaction**,

**as there is no swapping or displacement of ions during product formation.**

**Conclusion**

The reaction of KClO_{3} with H_{2}SO_{3} is a redox and exothermic reaction. KClO_{3} should be handled carefully as it is combustible in nature. H_{2}SO_{3 }and KClO_{3} are widely used as reducing and oxidizing agents, respectively.

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