Short Answer
An acidic salt is a salt that forms an acidic solution (pH < 7) when dissolved in water. Acidic salts are usually formed from a strong acid and a weak base.
For example, ammonium chloride (NH₄Cl) is an acidic salt because it is formed from hydrochloric acid (strong acid) and ammonia (weak base). In water, the NH₄⁺ ion hydrolyzes to produce H⁺ ions, making the solution acidic.
Detailed Explanation :
Acidic Salt
Acidic salts are salts that give a pH less than 7 in aqueous solutions. These salts are formed when a strong acid reacts with a weak base during neutralization. The resulting cation from the weak base has a tendency to hydrolyze in water, releasing hydrogen ions (H⁺) into the solution. The anion from the strong acid does not react with water because strong acids completely dissociate and their conjugate bases are very weak.
Acidic salts are important in chemistry because they help explain acid-base behavior of salts and are used in laboratories, industries, and biological applications.
Formation of Acidic Salts
Acidic salts are formed when:
Strong acid + Weak base → Acidic salt + Water
- Strong acids fully dissociate in water. Examples: HCl, H₂SO₄, HNO₃
- Weak bases partially dissociate. Examples: NH₃, Cu(OH)₂, Al(OH)₃
Example reactions:
- HCl + NH₃ → NH₄Cl
- H₂SO₄ + NH₃ → NH₄HSO₄
In these salts, the cation (NH₄⁺) hydrolyzes in water:
NH₄⁺ + H₂O → NH₄OH + H⁺
This releases H⁺ ions, lowering the pH and creating an acidic solution.
Properties of Acidic Salts
- Acidic pH
- The solution of acidic salts always has pH < 7.
- Hydrolysis
- Acidic salts undergo hydrolysis of the cation in water, producing H⁺ ions.
- Formation
- Always from strong acid + weak base.
- Chemical Reactivity
- Acidic salts can react with metals, carbonates, or hydroxides due to the presence of H⁺ ions.
- Common Examples
- Ammonium chloride (NH₄Cl)
- Ammonium sulfate ((NH₄)₂SO₄)
- Sodium bisulfate (NaHSO₄)
How Acidic Salts Work in Water
When an acidic salt dissolves:
- It dissociates into cation and anion.
- The cation of the weak base hydrolyzes:
- Example: NH₄⁺ + H₂O → NH₄OH + H⁺
- The anion of the strong acid does not react:
- Example: Cl⁻ remains unchanged.
- The net result: increase in H⁺ concentration → acidic solution.
Factors Affecting Acidity
- Strength of the Weak Base
- Weaker bases produce more hydrolysis → stronger acidity.
- Concentration of Salt
- Higher concentration → more H⁺ ions → lower pH.
- Nature of the Strong Acid
- Strong acids ensure their anions do not hydrolyze, keeping the acidic nature consistent.
- Temperature
- Hydrolysis may vary slightly with temperature, affecting H⁺ production.
Applications of Acidic Salts
- Laboratory Use
- Acidic salts are used to study hydrolysis, buffer systems, and acid-base reactions.
- Industrial Applications
- NH₄Cl is used in fertilizers, batteries, and metal cleaning.
- Its acidic property is useful in chemical processes.
- Biological Importance
- Acidic salts help maintain pH balance in biological systems, like ammonium salts in tissues.
- Environmental Significance
- Acidic salts in soil or water can slightly lower pH, influencing chemical and biological processes.
Examples of Acidic Salts
- Ammonium chloride (NH₄Cl) – used in fertilizers and medicine.
- Ammonium sulfate ((NH₄)₂SO₄) – used in agriculture.
- Sodium bisulfate (NaHSO₄) – used in cleaning agents.
These examples highlight that acidic salts are formed when a weak base reacts with a strong acid.
Conclusion
Acidic salts are salts formed from a strong acid and a weak base that produce a solution with pH less than 7 due to hydrolysis of the cation. Examples include NH₄Cl and NH₄HSO₄. The anion from the strong acid does not react, while the cation from the weak base releases H⁺ ions, making the solution acidic. Acidic salts are important in laboratory experiments, industries, biological systems, and environmental chemistry, where their controlled acidic nature is useful.