Practicing Success
What is the correct order of increasing acid strength? |
Phenol < Ethanol < Chloroacetic acid < Acetic acid Ethanol < Phenol < Chloroacetic acid < Acetic acid Ethanol < Phenol < Acetic acid < Chloroacetic acid Chloroacetic acid < Acetic acid < phenol < Ethanol |
Ethanol < Phenol < Acetic acid < Chloroacetic acid |
The correct answer is option 3. Ethanol < Phenol < Acetic acid < Chloroacetic acid. To explain the increasing acid strength of ethanol, phenol, acetic acid, and chloroacetic acid in detail, we must examine the structural factors that influence their ability to donate a proton \((H^+)\) and the stability of their conjugate bases. Ethanol \((C_2H_5OH)\) \(pK_a\): Approximately 16, indicating very weak acidity. Phenol \((C_6H_5OH)\) Phenol has the structure \(C_6H_5OH\), where the hydroxyl group is attached to a benzene ring. When phenol loses a proton, it forms the phenoxide ion \((C_6H_5O^-)\). The phenoxide ion is stabilized by resonance, as the negative charge can be delocalized over the aromatic ring. This resonance stabilization makes phenol a stronger acid than ethanol. \(pK_a\): Approximately 10, indicating moderate acidity. Acetic Acid \((CH_3COOH)\) Acetic acid has the structure \(CH_3COOH\), with a carboxyl group \((COOH)\). When acetic acid loses a proton, it forms the acetate ion \((CH_3COO^-)\). The acetate ion is stabilized by resonance, where the negative charge is delocalized between the two oxygen atoms. Additionally, the carbonyl group\((C=O)\) has an electron-withdrawing effect, further stabilizing the conjugate base. This makes acetic acid a stronger acid than phenol. \(pK_a\): Approximately 4.76, indicating relatively strong acidity. Chloroacetic Acid \((ClCH_2COOH)\) Chloroacetic acid has the structure \(ClCH_2COOH\), where a chlorine atom is attached to the carbon adjacent to the carboxyl group. When chloroacetic acid loses a proton, it forms the chloroacetate ion \((ClCH_2COO^-)\). The chloroacetate ion is stabilized by resonance, similar to the acetate ion. Additionally, the chlorine atom is highly electronegative and exerts a strong electron-withdrawing inductive effect, further stabilizing the conjugate base. This makes chloroacetic acid a stronger acid than acetic acid. \(pK_a\): Approximately 2.86, indicating strong acidity. Conclusion: Based on the ability to donate protons and the stabilization of their conjugate bases, the correct order of increasing acid strength is: \(\text{Ethanol} < \text{Phenol} < \text{Acetic acid} < \text{Chloroacetic acid}\). Thus, the correct answer is: Ethanol < Phenol < Acetic acid < Chloroacetic acid |