When calcium hydroxide reacts with sulfur dioxide, the precise products formed are calcium sulfite and water. This chemical interaction is a classic acid-base reaction, playing a crucial role in various industrial processes, particularly in environmental remediation.
The Chemical Reaction
The reaction between calcium hydroxide (Ca(OH)$_2$) and sulfur dioxide (SO$_2$) is a neutralization process. Calcium hydroxide is a base, commonly known as slaked lime, while sulfur dioxide, being a non-metal oxide, acts as an acidic gas when dissolved in water to form sulfurous acid (H$_2$SO$_3$).
According to the provided reference:
"Calcium hydroxide and sulfur dioxide reacts to give calcium sulphite and water."
The balanced chemical equation for this reaction is:
Ca(OH)$_2$ (aq) + SO$_2$ (g) → CaSO$_3$ (s) + H$_2$O (l)
This equation shows that aqueous calcium hydroxide reacts with gaseous sulfur dioxide to produce solid calcium sulfite and liquid water.
Understanding the Products
Let's look at the key components involved in this reaction:
| Component | Chemical Formula | Type | Role/Significance |
|---|---|---|---|
| Calcium Hydroxide | Ca(OH)$_2$ | Base | Common industrial chemical, absorbent, slaked lime |
| Sulfur Dioxide | SO$_2$ | Acidic Gas | Air pollutant, byproduct of fossil fuel combustion |
| Calcium Sulfite | CaSO$_3$ | Salt | Solid product, less soluble, key in desulfurization |
| Water | H$_2$O | By-product | Common solvent |
- Calcium Sulfite (CaSO$_3$): This is an inorganic salt that typically precipitates out of the solution as a solid. It is less soluble in water and is the primary solid product of this reaction. Calcium sulfite is a precursor to gypsum (calcium sulfate dihydrate) if further oxidized.
- Water (H$_2$O): The other product is water, which is a common byproduct of acid-base neutralization reactions.
Practical Applications: Flue Gas Desulfurization (FGD)
The reaction of calcium hydroxide with sulfur dioxide is of immense practical significance, particularly in environmental protection. One of its most prominent applications is in Flue Gas Desulfurization (FGD) systems, which are designed to remove sulfur dioxide (SO$_2$) from the exhaust flue gases of power plants and other industrial facilities. Sulfur dioxide is a major air pollutant contributing to acid rain and respiratory issues.
- Mechanism in FGD: In wet FGD systems, a slurry of calcium hydroxide (or limestone, which is calcium carbonate that can be converted to calcium hydroxide) is sprayed into the flue gas. The sulfur dioxide in the gas reacts with the calcium hydroxide to form calcium sulfite.
- Pollution Control: This process effectively captures and neutralizes SO$_2$, preventing its release into the atmosphere. The resulting calcium sulfite can then be oxidized further to produce calcium sulfate (gypsum), which is a useful material in construction.
- Industrial Relevance: FGD systems are crucial for compliance with environmental regulations and for mitigating the impact of industrial emissions on air quality.
Key Takeaways
- Calcium hydroxide reacts with sulfur dioxide in a neutralization reaction.
- The primary products of this reaction are calcium sulfite and water.
- This reaction is fundamental to flue gas desulfurization (FGD) technology, vital for controlling SO$_2$ emissions from industrial sources.
- It demonstrates how a basic compound can neutralize an acidic gas, transforming harmful pollutants into less harmful or even useful substances.
