What is the conjugate base of the following acids: HOCl H2SO4 H5C5NH2+
The Correct Answer and Explanation is:
The conjugate base of an acid is the species that remains after the acid donates a proton (H⁺). This principle follows the Brønsted-Lowry definition of acids and bases. Now, let’s analyze each given acid and identify its conjugate base.
- Hypochlorous acid (HOCl): HOCl is a weak acid, and it donates a proton to form its conjugate base. The removal of a proton leaves behind hypochlorite (OCl⁻), as shown in the equation:
HOCl→OCl⁻+H⁺\text{HOCl} \rightarrow \text{OCl⁻} + \text{H⁺}
- Sulfuric acid (H₂SO₄): H₂SO₄ is a strong acid and undergoes complete ionization in water. When it loses one proton, the resulting species is bisulfate (HSO₄⁻). Further loss of another proton results in sulfate (SO₄²⁻). The first dissociation is:
H₂SO₄→HSO₄⁻+H⁺\text{H₂SO₄} \rightarrow \text{HSO₄⁻} + \text{H⁺}
The second dissociation is:
HSO₄⁻→SO₄²⁻+H⁺\text{HSO₄⁻} \rightarrow \text{SO₄²⁻} + \text{H⁺}
- Pyridinium ion (H₅C₅NH₂⁺): The pyridinium ion is the protonated form of pyridine (C₅H₅N). When it donates a proton, the resulting conjugate base is pyridine (C₅H₅N), as represented by:
H₅C₅NH₂⁺→C₅H₅N+H⁺\text{H₅C₅NH₂⁺} \rightarrow \text{C₅H₅N} + \text{H⁺}
Explanation
The concept of conjugate acid-base pairs is fundamental in acid-base chemistry. Acids donate protons and transform into their conjugate bases, while bases accept protons and turn into their conjugate acids.
For HOCl, the loss of an H⁺ results in hypochlorite (OCl⁻), which can act as a weak base in aqueous solutions. The equilibrium between HOCl and OCl⁻ plays an important role in disinfection and water treatment.
Sulfuric acid, being diprotic, has two conjugate bases. HSO₄⁻ is relatively acidic, allowing it to donate another proton to form SO₄²⁻. The sulfate ion is highly stable and commonly found in salts such as sodium sulfate (Na₂SO₄).
The pyridinium ion originates from pyridine, a widely used organic compound in pharmaceuticals and catalysts. Its conjugate base, pyridine (C₅H₅N), is a weak base due to the nitrogen’s ability to accept a proton.
Understanding these conjugate bases is essential for predicting acid-base behavior, equilibrium reactions, and buffer systems in various chemical applications.
