Levelling Effect

 Leveling Effect

WRITTEN BY: RANA FAHAD ALI

COMPOSED BY: MISBAH UD DIN

BROUGHT TO YOU BY: CHEMISTREEPK

Intro

Leveling effect or solvent leveling refers to the effect of solvent on the properties of acids and bases. In other words;

"The relative strength of various acids is equal in aqueous solutions. Because Different acids have almost same pka value in water."

Explanation

Acids and bases change their strengths by changing the solvent. Non-aqueous solvents like ammonia, amides (RCONH2), hydrazine, etc. are good proton acceptors and will help acids to ionize in them, they are called basic solvents. As a result of this, all acids tend to become strong in a basic solvent. Such solvents are said to exert a leveling effect on the strength of acids.
The reverse is true for acidic solvents like CH3COOH, HCOOH, hydrogen halide (HX), etc. in which all bases tend to become strong. Such acidic solvents however tend to decrease the acid strength of the acids and tend to exert a differentiating effect on the strength of the acids. Thus water behaves as leveling solvent for acids such as HCl4, HI, HBr, HNO3, and HCl. And bases such as NaOH, NaNH2, and NaOC2H5. So, in the aqueous medium, the acid strength is similar due to leveling effect of water. Therefore to compare their relative strengths of acids and bases, a solvent should be selected that ionizes the strong acids and bases to different extents, such a solvent is called the differentiated
solvent. For Example, acetic acid is a differentiating solvent towards halogen acids, and their ionization increases with an increase in the atomic number of halogens. That is acid strength decreases as;

HI > HBr > HCl

So, the acetic acid is used to determine the relative strength of strong acids like HClO4, H2SO4, HNO3, Halogen acids, etc. and the following trend has been observed; 

HClO4 > HI > HBr > HCl > H2SO4 > HNO3

However, acetic acid exerts a leveling effect to determine the basic structure of bases. It brings basic strength on the same level. Consequently, the relative strength of ammonia, primary amines, secondary amines, tertiary amines, etc. can not be distinguished and their basic strength gets enhanced and leveled. In general, acidic solvents tend to differentiate between acids and level off bases while basic solvents tend to different bases and level off acids.

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