Calcium hydroxide is a strong base and reacts easily with sulphurous acid. Let us discuss more about the reaction between H2SO3 and Ca(OH)2.
Ca(OH)2 is a strong Lewis base that is white in color. It reacts with H2SO3, an odorless, weak Lewis acid. Ca(OH)2 completely dissociates to give hydroxide ions in water. H2SO3 is the aqueous solution of sulfur dioxide and an oxyacid of sulphuric acid. It is an important constituent of acid rain.
In this article, let us discuss the chemical properties of the reaction H2SO3 + Ca(OH)2, like the type of reaction, buffer solution, conjugate pairs and balancing method.
What is the product of H2SO3 and Ca(OH)2?
Calcium sulphite and water are formed when calcium hydroxide combines with sulphurous acid.
Ca(OH)2 + H2SO3 ————> CaSO3 + 2H2O
What type of reaction is H2SO3 + Ca(OH)2?
H2SO3 + Ca(OH)2 is categorized as a neutralization reaction, since a weak acid neutralizes a strong base to produce salt and water.
How to balance H2SO3 + Ca(OH)2?
The steps to balance H2SO3 + Ca(OH)2 is as follows –
H2SO3 + Ca(OH)2 = CaSO3 + H2O.
- Count the number of moles of each element involved in the reaction, in both the reactant and product side.
| Elements | Reactant side | Product side |
|---|---|---|
| Ca | 1 | 1 |
| S | 1 | 1 |
| O | 5 | 4 |
| H | 4 | 2 |
- We find that the product side is devoid of 1 mole of oxygen atom and 2 moles of hydrogen atom.
- To equalize the number of reactant and product side moles, we add 2 moles of H2O on the product side.
- Thus, the overall balanced reaction is given by –
- H2SO3 + Ca(OH)2 = CaSO3 + 2H2O
H2SO3 + Ca(OH)2 titration
An acid-base titration between H2SO3 and Ca(OH)2 is performed to measure the amount of calcium and hydroxide ions. The procedure for titration is explained below.
Apparatus
Burette, burette holder, pipette, conical flask, volumetric flask, wash bottle, and beakers.
Indicator
Phenolphthalein is an acid-base indicator used to detect the end point of this titration.
Procedure
- Standardized H2SO3 is taken in a burette, while calcium hydroxide is taken in a conical flask.
- Add 2 drops of phenolphthalein indicator.
- H2SO3 is slowly added from the burette into the conical flask with constant shaking until the solution turns from colorless to light pink.
- The above procedure is repeated for 3 concordant readings.
- Unknown normality of Ca(OH)2 is calculated using the formula, V1S1=V2S2.
H2SO3 + Ca(OH)2 net ionic equation
The net ionic equation between H2SO3 + Ca(OH)2 is:
H2SO3 (aq) + Ca2+ (aq) + 2OH– (aq) = CaSO3 (s) + 2H2O (l)
The following steps are followed to derive the net ionic equation:
- Balance the given molecular equation to get –
- H2SO3 + Ca(OH)2 = CaSO3 + 2H2O
- Indicate 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) + 2OH– (aq) = CaSO3 (s) + 2H2O (l)
- We find that the complete ionic equation is the same as the net ionic equation.
H2SO3 + Ca(OH)2 conjugate pairs
- H2SO3 and HSO3– are the conjugate acid-base pairs.
- OH– and H2O are the conjugate acid-base pairs.
H2SO3 + Ca(OH)2 intermolecular forces
- In H2SO3, Van der Waals forces, dipole-dipole interactions and London dispersion forces are the intermolecular forces that bind the hydrogen and sulphite ions together.
- In Ca(OH)2, strong electrostatic attraction forces between Ca2+ and OH– ions, as calcium hydroxide is an ionic compound.
H2SO3 + Ca(OH)2 reaction enthalpy
The standard reaction enthalpy of the reaction between H2SO3 and Ca(OH)2 is -358.6 KJ/mol.
Is H2SO3 + Ca(OH)2 a buffer solution?
H2SO3 + Ca(OH)2 is a buffer solution. It is an indirect acidic buffer as the salt calcium sulphite formed is from a weak acid and strong base reaction.
Is H2SO3 + Ca(OH)2 a complete reaction?
H2SO3 + Ca(OH)2 is not a complete reaction, as H2SO3, a weak acid, remains in the solution.
Is H2SO3 + Ca(OH)2 an exothermic reaction?
H2SO3 + Ca(OH)2 is an exothermic reaction, as the reaction enthalpy is negative, and the heat generated drives the reaction in the forward direction.
Is H2SO3 + Ca(OH)2 a redox reaction?
The reaction between H2SO3 and Ca(OH)2 is not a redox reaction, as there is no change in the oxidation states of the elements.
Is H2SO3 + Ca(OH)2 a precipitation reaction?
H2SO3 + Ca(OH)2 is a precipitation reaction as the product formed is a white precipitate of calcium sulphite, insoluble in water.
Is H2SO3 + Ca(OH)2 an irreversible reaction?
H2SO3 + Ca(OH)2 is an irreversible reaction because calcium sulphite formed is a residue which is insoluble in water. So, a backward reaction does not take place.
Is H2SO3 + Ca(OH)2 a displacement reaction?
The reaction between H2SO3 + Ca(OH)2 is an example of a double displacement reaction, because the anions and cations swap their places to form salt and water.
Conclusion
This article compiles the reaction between H2SO3 and Ca(OH)2. Sulphurous acid is used widely as a strong reducing agent, while calcium hydroxide (also called slaked lime) is used in construction and as a dental filler.
Read more about following H2SO3 facts
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