When calcium hydroxide reacts with an acid, a neutralization reaction occurs, resulting in the formation of a salt and water. This fundamental chemical process is a classic example of an acid-base reaction.
The Neutralization Process
Calcium hydroxide, with the chemical formula Ca(OH)$_2$, is known as a fairly strong base. Bases are substances that can accept protons (H$^+$ ions) or donate hydroxide ions (OH$^-$ ions) in a solution. Acids, conversely, are substances that donate protons (H$^+$ ions). When a base and an acid are combined, their reactive components counteract each other, leading to a neutralization where the acidic and basic properties are cancelled out, typically producing a neutral solution (pH of 7) if the stoichiometry is exact.
Specific Example: Reaction with Hydrochloric Acid
To illustrate this, let's consider the reaction with hydrochloric acid (HCl), a strong acid. As highlighted in chemical principles:
"Calcium hydroxide is a fairly strong base, and hydrochloric acid is a strong acid. The two substances readily react with and neutralise each other, forming the soluble salt calcium chloride (CaCl$_2$) and water."
In this specific reaction:
- Calcium hydroxide (Ca(OH)$_2$) provides the hydroxide ions (OH$^-$).
- Hydrochloric acid (HCl) provides the hydrogen ions (H$^+$).
- The H$^+$ ions combine with the OH$^-$ ions to form water (H$_2$O).
- The remaining ions, calcium (Ca$^{2+}$) from the base and chloride (Cl$^-$) from the acid, combine to form the salt, calcium chloride (CaCl$_2$).
Key Products and Their Properties
The primary products of this neutralization reaction are a salt and water.
| Reactant / Product | Nature / Type | Chemical Formula | Key Property |
|---|---|---|---|
| Calcium Hydroxide | Fairly Strong Base | Ca(OH)$_2$ | Neutralizes acids, provides hydroxide ions. Commonly known as slaked lime. |
| Acid | Acid | e.g., HCl | Donates hydrogen ions, reacts with bases. |
| Calcium Chloride | Soluble Salt | CaCl$_2$ | A salt formed from the cation of the base and the anion of the acid; it is soluble in water. |
| Water | Neutral Compound | H$_2$O | Formed from the combination of H$^+$ and OH$^-$ ions; essential solvent. |
Practical Implications and Applications
The reaction between calcium hydroxide and acids has several practical applications:
- pH Adjustment: Calcium hydroxide, often used in its aqueous form as "limewater," is commonly used to raise the pH of acidic solutions or soils. For example, it's used in agriculture to sweeten acidic soils, making them more suitable for certain crops.
- Wastewater Treatment: It is employed in wastewater treatment facilities to neutralize acidic industrial effluents before they are discharged, preventing environmental damage.
- Industrial Processes: Calcium hydroxide is a component in many industrial processes, including the production of mortar, plaster, and cement, where its basic properties are utilized to control acidity or facilitate other reactions.
This reaction effectively converts potentially harmful or undesirable acidic substances into less reactive and often more environmentally benign compounds.
