Calcium oxide and sulphurous acid are inorganic compounds with chemical formulas, CaO and H2SO3, respectively. Let us explore more about the reaction between H2SO3 and CaO.
CaO, a Lewis base, is a white, hygroscopic, crystalline powder. H2SO3 is a colorless, corrosive oily liquid. CaO interacts with acids easily due to its basic nature. A weak acid-strong base reaction is initiated when H2SO3 is added to CaO.
In this article, we will learn about a few properties based on the reaction H2SO3 + CaO, like the type of reaction, the product formed, buffer solution, conjugate pairs etc.
What is the product of H2SO3 and CaO?
Calcium sulphite and water are formed when CaO reacts with H2SO3.
CaO + H2SO3 ———-> CaSO3 + H2O
What type of reaction is H2SO3 + CaO?
H2SO3 + CaO is classified as an acid-base reaction, as an acid neutralizes a strong base to produce salt and water.
How to balance H2SO3 + CaO?
The equation for the reaction between H2SO3 and CaO is balanced using the following steps.
- The general equation is H2SO3 + CaO = CaSO3 + H2O.
- Calculate the number of moles of each element involved in both the reactant and product side of the reaction.
| Elements | Reactant side | Product side |
|---|---|---|
| Ca | 1 | 1 |
| S | 1 | 1 |
| O | 4 | 4 |
| H | 2 | 2 |
- The number of moles of each element on the reactant side is exactly equal to that on the product side.
- Thus the reaction is self-balanced, and the overall balanced reaction is given by –
- H2SO3 + CaO = CaSO3 + H2O
H2SO3 + CaO titration
An acid-base titration between H2SO3 and CaO can be performed to estimate the strength of sulphurous acid. The procedure for titration is as follows –
Apparatus
Burette, burette holder, pipette, distilled water, conical flask, volumetric flask, wash bottle, stirrer, and beakers.
Indicator
Phenolphthalein is the acid-base indicator used to detect the end point of the titration.
Procedure
- Calcium oxide, a white solid, is soluble in water, and forms calcium hydroxide, Ca(OH)2.
- 0.1 N freshly prepared Ca(OH)2 is taken in the burette.
- 10 ml of H2SO3 is pipetted out into a clean conical flask.
- Add 1-2 drops of phenolphthalein indicator.
- Add Ca(OH)2 dropwise from the burette into the conical flask with constant swirling until the appearance of light pink color. This is the end point of titration.
- Note the volume of Ca(OH)2 required to neutralize the sulphurous acid solution.
- The above procedure is repeated for 3 consistent readings.
- The strength of H2SO3 is calculated using the formula, SCa(OH)2 VCa(OH)2 = SH2SO3 VH2SO3
H2SO3 + CaO net ionic equation
The net ionic equation between H2SO3 + CaO is –
H2SO3 (aq) + Ca2+ (aq) + O2- (aq) = CaSO3 (s) + H2O (l)
The following steps are followed to derive the net ionic equation:
- Write the balanced molecular equation along with the physical state.
- H2SO3 (aq) + CaO (aq) = CaSO3 (s) + H2O (l)
- Now, write the ionic form of each of the substances existing in aqueous form and capable of complete dissociation in water. H2SO3 is a weak electrolyte that does not completely dissociate into ions in aqueous form. Hence, the complete ionic equation is –
- H2SO3 (aq) + Ca2+ (aq) + O2- (aq) = CaSO3 (s) + H2O (l)
- We find that the complete ionic equation is identical to the net ionic equation.
- H2SO3 (aq) + Ca2+ (aq) + O2- (aq) = CaSO3 (s) + H2O (l)
H2SO3 + CaO conjugate pairs
- H2SO3 and HSO3– are the conjugate acid-base pairs.
- Conjugate acid of calcium oxide is calcium hydroxide.
H2SO3 + CaO intermolecular forces
- In H2SO3, London dispersion forces, Van der Waals forces, and dipole-dipole interactions are the intermolecular forces that bind the hydrogen and sulphite ions together.
- In CaO, strong ionic attractive forces exist between the cation Ca2+ and anion O2–, as calcium oxide is an ionic compound.
H2SO3 + CaO reaction enthalpy
The standard reaction enthalpy of the reaction between H2SO3 and CaO is negative.
Is H2SO3 + CaO a buffer solution?
H2SO3 + CaO is a buffer solution. It is an indirect acidic buffer solution, as the reaction constitutes a weak acid and calcium sulphite salt, formed from a weak acid and a strong base.
Is H2SO3 + CaO a complete reaction?
H2SO3 + CaO is not a complete reaction, as H2SO3, a weak acid, remains in the solution due to its poor dissociation.
Is H2SO3 + CaO an exothermic reaction?
H2SO3 + CaO is an exothermic reaction, as the reaction enthalpy is negative.
Is H2SO3 + CaO a redox reaction?
The reaction between H2SO3 and CaO is not a redox reaction, as neither oxidation nor reduction of any element takes place simultaneously.
Is H2SO3 + CaO a precipitation reaction?
H2SO3 + CaO is a precipitation reaction as the product formed is a white precipitate of calcium sulphite, which is insoluble in water.
Is H2SO3 + CaO an irreversible reaction?
H2SO3 + CaO is an irreversible reaction because of the formation of calcium sulphite precipitate, which is insoluble in water.
Is H2SO3 + CaO a displacement reaction?
The reaction between H2SO3 + CaO is an example of a double displacement reaction, because the anions and cations switch places to form salt and water.
Conclusion
Sulphurous acid and calcium oxide are widely used as industrial agents. The product formed in this reaction, calcium sulphite, is used in flue-gas desulphurization. CaO (also called quick lime) is a primary ingredient in the cement industry.
Read more about following H2SO3 facts
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