Leveling effect
The leveling effect is the ability of a solvent to enhance the strength of weak acids or bases to that of strong ones. Leveling solvent is the solvent in which total proton transfer happens or the solute is entirely ionized. Water (H2O) is a popular example of a leveling solvent. A strong acid’s strength is limited (“leveled”) by the basicity of the solvent.
Using water as the solvent simplifies the explanation of leveling. In this case, the action will prevent the presence of bases stronger than hydroxide in the solution. The strong base will no longer exist and will be deprotonated to generate a hydroxide ion and the corresponding cation. As a result, when the solvent is water, no base stronger than OH- can be utilized. In terms of base strength, this indicates that all bases stronger than the hydroxide ion are nearly indistinguishable in aqueous solution.
Basic solvents have a leveling effect on weak acids. In general, strong acids readily give H+, whereas basic solvents readily attract H+ from weak acids, resulting in the same strength for both strong and weak acids.
Acidic solvents also have a leveling impact on weak bases; ordinarily, a strong base pulls H from the solvent, in weak bases, the acidic solvent easily donates or provides its proton to it, implying that weak and strong bases are of comparable strength.
Examples:
1-Glacial acetic acid has a leveling effect on bases like amines, indicating that they are strong bases in acetic acid.
2-Liquid ammonia and ethylene diamine, which are more basic than H20, have leveling effects on both mineral and carboxylic acids (acetic); in such solvents, they all have roughly the same strength.
The leveling effect of liquid ammonia
The leveling effect, also known as solvent leveling, is the influence of a solvent on the characteristics of acids and bases. A strong acid’s strength is limited (leveled) by the basicity of the solvent. Similarly, the acidity of the solvent balances out the strength of a strong base.
Because these acids ionize in Liq.NH3 to create NH4+ cations, liquid ammonia (NH3) works as a leveling solvent for HCl (Strong acid) and CH3COOH (Weak acid).
HCl + NH3 → Cl – + NH4 +
CH3COOH + NH3 → CH3COO – + NH4 +
Differentiating effect
Differentiating solvent is the solvent in which distinct acids dissociate to varying degrees and so have different strengths. Weak bases serve as acid-specific solvents. It is the solvent’s ability to distinguish between the strength of acids and bases:
Examples:
Water is a distinguishing solvent for amines (weak bases), which are far weaker than mineral alkalies (NaOH & KOH).
When HClO4, HCl, and HNO3 are dissolved in glacial acetic acid, only HClO4 is the strong acid, indicating that acetic acid distinguishes between the strength of mineral acids.
CH3COOH +HClO4 ⇌ CH3COOH2+ + ClO4–
CH3COOH +HBr ⇌ CH3COOH2+ + Br–
Solvent types based on proton interaction
Solvents are classified into four kinds based on proton interaction.
(i) Protophilic solvents: Solvents that accept protons more readily, such as water, alcohol, liquid ammonia, and so on.
(ii) Protogenic solvents: Solvents that have the ability to generate protons, such as water, liquid hydrogen chloride, glacial acetic acid, and so on.
iii) Amphiprotic solvents: Solvents that act as both protophilic and protogenic, such as water, ammonia, ethyl alcohol, and so on.
(iv) Aprotic solvents: Solvents that do not donate or accept protons, such as benzene, carbon tetrachloride, carbon disulfide, and so on.
HCl acts as an acid in H2O, a stronger acid in NH3, a weak acid in CH3COOH, neutral in C6H6, and a weak base in HF.
References
- K.R palak,2017, Stereochemistry. Pairavi Prakashan.
- Smith M. B. & March J. (2007). March’s advanced organic chemistry : reactions mechanisms and structure (6. ed.). Wiley-Interscience.
- Bahl A. & Bahl B. S. (2006). A textbook of organic chemistry (for b. sc. students) (18th rev. & enlarged ed. 1st multicolour illustrative). S. Chand.
- https://slideplayer.com/slide/6933566/
- https://teachmint.storage.googleapis.com/public/976158958/StudyMaterial/27bc2748-4fc4-4242-a8c9-182f0d771484.pdf
