Hydrolysis

What is hydrolysis?

Literally hydrolysis means breakage by water. We know that when an acid and a base react with each other a salt plus water is formed:

AH +BOH <–> AB + H₂O

It is conceivable that if the process is reversible, i.e., that when a salt dissolves in water, an acid or base may appear in the medium, assigning it a certain pH.

AB + H₂O <–> AH + BOH

The hydrolysis reaction occurs only with certain salts, and four different cases can occur:

1. strong acid-strong base salt:

ClNa neither the cation nor the anion is hydrolyzed.

ClNa <–> Cl^– + Na⁺

Cl^– + H₂O (no) <–> ClH + OH^–

Na⁺ + H₂O (no) <–> NaOH + H⁺

As neither the cation nor the anion can be hydrolyzed, the pH will be neutral.

1. strong acid-weak base salt:

ClNH₄ hydrolyzable cation salt

ClNH₄ <–> Cl^– + NH₄⁺

Cl^– + H₂O (no) <–> ClH + OH^–

NH₄⁺ + H₂O <–> NH₄OH + H⁺

K_h = [NH₄OH]·[H⁺]/[NH₄⁺] [H₂O] = cte

Multiplying by [OH^–]

K_h = [NH₄OH]·[H⁺]·[OH^–]/[NH₄⁺]·[OH^–] = [NH₄OH]·K_w/[NH₄⁺]·[OH^–] = K_w/K_b

K_h = K_w/K_b the stronger the base the less it hydrolyzes

NH₄OH <–> NH₄⁺ + OH^–

K_b = [NH₄⁺]·[OH^–]/[NH₄OH]

1. weak acid-strong base salt:

CNK hydrolyzable anion salt

CNK <–> CN^– + K⁺

K⁺ + H₂O (no) <–> KOH + H⁺

CN^– + H₂O <–> CNH + OH^–

K_h = [CNH]·[OH^–]/[CN^–] [H₂O] = cte

Multiplying by [H⁺]

K_h = [CNH]·[OH^–]·[H⁺]/[CN^–]·[H⁺] = [CNH]·K_w/[CN^–]·[H⁺] = K_w/K_a

K_h = K_w/K_a the stronger the acid the less it will hydrolyze

CNH <–> CN^– + H⁺

K_a = [CN^–]·[H⁺]/[CNH]

1. weak acid-weak base salt:

CH₃COONH₄ sal de catión y anión hidrolizables

CH₃COONH₄ -> CH₃COO^– + NH₄⁺

CH₃COO^– + H₂O -> CH₃COOH + OH^–

NH₄⁺ + H₂O -> NH₄OH + H⁺

————

CH₃COO^– + NH₄⁺ + H₂O -> CH₃COOH + NH₄OH

K_h = [NH₄OH]·[ CH₃COOH]/ [CH₃COO^–] [NH₄⁺] [H₂O] = cte

Multiplying by [OH^–] y [H⁺]

K_h = [CH₃COOH]·[NH₄OH]·[H⁺]·[OH^–]/[ CH₃COO^–][NH₄⁺]·[H⁺]·[OH^–]

= K_w/K_a·K_b

Degree of hydrolysis

The degree of hydrolysis (α) is the percentage of salt that is hydrolyzed.

If α = 1 the salt is completely hydrolyzed.

If α = 0 there is no hydrolysis.

The relationship between the degree of hydrolysis and the hydrolysis constant is:

Ac^– + H₂O <–> AcH + OH^–

Equilibrium C(1-α) Cα + Cα

K_h = cα²/(1-α)

The degree of hydrolysis and therefore the hydrolysis of a salt increases with temperature, with dilution and with the greater weakness of either the acid or the corresponding base.

Video about Hydrolysis

FAQ

What is hydrolysis and what is it used for?

This process is characterized as a chemical reaction catalyzed by an enzyme that uses water to break a molecule into two or more fractions. Therefore, when applied to a medium containing proteins, these are broken down into smaller amino acid chains, the hydrolyzed proteins.

What does hydrolysis release?

The energy released by the hydrolysis (breakdown) of ATP is used to drive many cellular reactions that require energy. Structure of ATP. At the center of the molecule is a sugar (ribose), attached to the base adenine on one side and a chain of three phosphates on the other.