Leveling effect
Encyclopedia
The term leveling effect refers to a solvent
's ability to level the effect of a strong acid
or base
dissolved in it.
ion
(H3O+) in the following reaction (where "HA" is a generic strong acid such as hydrochloric acid
(HCl)):
HA + H2O -> A- + H3O+
Any acid that is stronger than H3O+ reacts with H2O to form H3O+; therefore, no acid can be stronger than H3O+ in H2O.
This is true with any solvent, although usually to a lesser extent than with water. Bases may be also leveled in solvents.
(NaNH2) and water:
H-O-H + NH2- --> H-O- + NH3
(Stronger Acid) (Stronger Base) --> (Weaker Base) (Weaker Acid)
The amide ion reacts with water to produce a solution containing hydroxide
ions (a much weaker base) and ammonia
.
. Similarly a weak acid has less tendency to donate protons than a strong acid. As a result a strong acid such as perchloric acid
exhibits more strongly acidic properties than a weak acid such as acetic acid
when dissolved in a weakly basic solvent. On the other hand, all acids tend to become indistinguishable in strength when dissolved in strongly basic solvents owing to the greater affinity of strong bases for protons. This is called the leveling effect. Strong bases are leveling solvents for acids, weak bases are differentiating solvents for acids.
To use acids stronger than the hydroxonium ion, use a solvent that is a stronger acid than water.
Solvent
A solvent is a liquid, solid, or gas that dissolves another solid, liquid, or gaseous solute, resulting in a solution that is soluble in a certain volume of solvent at a specified temperature...
's ability to level the effect of a strong acid
Strong acid
A strong acid is an acid that ionizes completely in an aqueous solution by losing one proton, according to the equationFor sulfuric acid which is diprotic, the "strong acid" designation refers only to dissociation of the first protonMore precisely, the acid must be stronger in aqueous solution than...
or base
Base (chemistry)
For the term in genetics, see base A base in chemistry is a substance that can accept hydrogen ions or more generally, donate electron pairs. A soluble base is referred to as an alkali if it contains and releases hydroxide ions quantitatively...
dissolved in it.
Process
When a strong acid is dissolved in water, it reacts with it to form hydroniumHydronium
In chemistry, a hydronium ion is the cation , a type of oxonium ion produced by protonation of water. This cation is often used to represent the nature of the proton in aqueous solution, where the proton is highly solvated...
ion
Ion
An ion is an atom or molecule in which the total number of electrons is not equal to the total number of protons, giving it a net positive or negative electrical charge. The name was given by physicist Michael Faraday for the substances that allow a current to pass between electrodes in a...
(H3O+) in the following reaction (where "HA" is a generic strong acid such as hydrochloric acid
Hydrochloric acid
Hydrochloric acid is a solution of hydrogen chloride in water, that is a highly corrosive, strong mineral acid with many industrial uses. It is found naturally in gastric acid....
(HCl)):
HA + H2O -> A- + H3O+
Any acid that is stronger than H3O+ reacts with H2O to form H3O+; therefore, no acid can be stronger than H3O+ in H2O.
This is true with any solvent, although usually to a lesser extent than with water. Bases may be also leveled in solvents.
Example
Solomons & Fryhle describe the leveling effect, using the example of the reaction between sodium amideSodium amide
Sodium amide, commonly called sodamide, is the chemical compound with the formula NaNH2. This solid, which is dangerously reactive toward water, is white when pure, but commercial samples are typically gray due to the presence of small quantities of metallic iron from the manufacturing process...
(NaNH2) and water:
H-O-H + NH2- --> H-O- + NH3
(Stronger Acid) (Stronger Base) --> (Weaker Base) (Weaker Acid)
The amide ion reacts with water to produce a solution containing hydroxide
Hydroxide
Hydroxide is a diatomic anion with chemical formula OH−. It consists of an oxygen and a hydrogen atom held together by a covalent bond, and carrying a negative electric charge. It is an important but usually minor constituent of water. It functions as a base, as a ligand, a nucleophile, and a...
ions (a much weaker base) and ammonia
Ammonia
Ammonia is a compound of nitrogen and hydrogen with the formula . It is a colourless gas with a characteristic pungent odour. Ammonia contributes significantly to the nutritional needs of terrestrial organisms by serving as a precursor to food and fertilizers. Ammonia, either directly or...
.
Leveling and differentiating solvents
A weakly basic solvent has less tendency than a strongly basic one to accept a protonProton
The proton is a subatomic particle with the symbol or and a positive electric charge of 1 elementary charge. One or more protons are present in the nucleus of each atom, along with neutrons. The number of protons in each atom is its atomic number....
. Similarly a weak acid has less tendency to donate protons than a strong acid. As a result a strong acid such as perchloric acid
Perchloric acid
Perchloric acid is the inorganic compound with the formula HClO4. Usually encountered as an aqueous solution, this colourless compound is a strong acid comparable in strength to sulfuric and nitric acids. It is a powerful oxidizer, but its aqueous solutions up to appr. 70% are remarkably inert,...
exhibits more strongly acidic properties than a weak acid such as acetic acid
Acetic acid
Acetic acid is an organic compound with the chemical formula CH3CO2H . It is a colourless liquid that when undiluted is also called glacial acetic acid. Acetic acid is the main component of vinegar , and has a distinctive sour taste and pungent smell...
when dissolved in a weakly basic solvent. On the other hand, all acids tend to become indistinguishable in strength when dissolved in strongly basic solvents owing to the greater affinity of strong bases for protons. This is called the leveling effect. Strong bases are leveling solvents for acids, weak bases are differentiating solvents for acids.
Solution
To use bases stronger than the hydroxide ion, use a solvent that is a weaker acid than water.To use acids stronger than the hydroxonium ion, use a solvent that is a stronger acid than water.