[1] ANIONIC SALT HYDROLYSIS:

When a salt is dissolved in a solvent, it first dissociates into its constituent ions. This process is called dissolution. Now, if these ions chemically react with water, the process is called hydrolysis.

Salt hydrolysis is may be consider as the reverse of process of neutralization

We can also say that “combination of any of the ion furnished by the salt with water molecules is called hydrolysis “

Cationic hydrolysis will make the solution acidic but anionic hydrolysis will make the solution basic

(1) NEUTRAL SALTS: (Salts of strong acids and strong bases)

  A salts formed by complete neutralization of strong acid and strong base are called neutral salt such salts will not undergoes hydrolysis so aqueous solution of such salts be must neutral.

The salts that undergo hydrolysis after dissolution are
(2) ALKALINE SALTS:(Salts of weak acids and strong bases)
(3) ACIDIC SALTS:(Salts of weak bases and strong acids)
(4)  Salts of weak acids and weak bases

(1) ANIONIC HYDROLYSIS OR ALKALINE SALTS HYDROLYSIS:

                  (Salt of a Weak Acid and Strong Base) 

      Let us take a certain amount of weak acid (CH₃COOH) and add to it the same amount of a strong base (NaOH). They will react to produce CH₃COONa. 

      CH₃COONa being a strong electrolyte, completely dissociates into its constituent ions.

      Now, the ions produced would react with H₂O. This process is called hydrolysis

We know that NaOH is a strong base and therefore it would be completely dissociated to give Na⁺ and OH^– ions.

      Canceling Na⁺ on both the sides,

We can note here that ions coming from strong bases do not get hydrolysed. We should note here that the solution will be basic. This is because the amount of CH₃COOH produced and OH^– produced are equal. But CH₃COOH will not completely dissociate to give H⁺ ions. Therefore [OH^–] ions will be greater than [H⁺] ions.

      Since the reaction is at equilibrium,

This equilibrium constant K_c is given a new symbol, K_h

If we multiply and divide the above equation by [H⁺] of the solution, then

CASE (1): If a is very much less than 1, then 1-a= 1 this approximation valid when C/Kh is greater than 100”

CASE (2): If C/Kh is lower than 100 than calculate h by formation of quadratic equation.

ILLUSTRATIVE EXAMPLE (1): A 0.0258 M solution of the sodium salt, NaH of the weak monoprotic acid, HA has a pH of 9.65. Calculate Ka of the acid AH.

ILLUSTRATIVE EXAMPLE (2): What is the pH of 0.10 M CH₃COONa solution. Hydrolysis constant of sodium acetate is 5.6 × 10^-10   ?

SOLUTION: Hydrolysis of the salt may be represented as

ILLUSTRATIVE EXAMPLE (3): Calculate pH of 1.0 x 10^-3 M Sodium phenolate (Na⁺O^-C₆H₅ ) Ka for C₆H₅OH is 1.0 x10^{-10 .}

SOLUTION:  (Ans-  pH=10.43)

(2) CATIONIC HYDROLYSIS    OR  ACIDIC SALTS HYDROLYSIS:

         (Salt of a Weak Base and a Strong Acid)    .......

SALTS AND SALT HYDROLYSIS

(1) Salts are the compounds formed by neutralization between acids and bases which are containing at least one positive part (Cation) other than H⁺ and also at least  one Negative part (Anion) other than OH^-.

(2) Salts may taste salty, bitter, a stringer or sweet or tasteless

(3) Solution of salts may be acidic, basic or neutral.

(4) Fused salts and their aqueous solutions conduct electricity and undergo electrolysis

(5)The salts are generally crystalline solids

CLASSIFICATION OF SALTS:

These salts may be classified into four categories.

(A) SIMPLE SALTS:

The salts formed by the neutralization process between acid and base. These are of three types.

(1) Normal salt:     

The salt formed by the loss of all possible protons (replaceable H⁺ ions)

For example NaCl, NaNO₃, K₂SO₄, Ca₃ (PO4)₂, Na₃BO₃, Na₂HPO, NaH₂PO₂ etc.

(2) Acidic salts:

Salts formed by incomplete neutralization of polybasic acid. Such salts contain one or more replaceable H atom.

For examples NaHCO3, NaHSO₄, NaH₂PO₄, Na₂HPO₄ etc.

Above salts when neutralised by base form normal salts.

(3) Basic salts:

Salts formed by incomplete neutralization of poly acidic bases are called basic salts. These salt contain one or more hydroxyl groups.basic salt when neutralised by acids form normal salts.

Ex. Zn(OH)Cl,  Mg(OH)Cl,  Fe(OH)₂Cl, Bi(OH)₂ etc.

(B) DOUBLE SALTS:

(1)The addition compounds formed by the combination of two simple salts are termed as double salts.

(2) Double salts are stable in solid state only.

(3) When dissolved in water, it furnishes all the ions present in the simple salt form which it has been constituted.

(4)The solution of double salt shows the properties of the samples salts from which it has been constituted

For examples

Mohar’s salt-FeSO₄ (NH₄)₂SO₄ .6H₂O (Ferrous ammonium sulphate)

Alum’s- K₂SO₄Al₂ (SO4)₃. 24H₂O (Potassium ammonium sulphate)

Karnalite- KCl.MgCl_2.6 (H₂O)

Dolomite- CaCO₃.MgCO₃ or CaMg (CO₃)₂

(C) COMPLEX SALTS:

(1) Complex salts are formed by combination of two simple salts or molecular compounds.

      For examples   K₄Fe (CN)₆, Co(NH₃)₆ SO₄ etc.

(2) Complex salts are stable in solid states as well as solutions

(3) Complex salts On dissolving in water, if furnishes a complex ion.

(4) The properties of the solution are different from the properties of the substance from which it has been constituted.

(D) MIXED SALTS:

(1)The salt which furnishes more than one cation or more than one anion when dissolved in water is Called mixed salt.

FOR EXAMPLE - CaOCl₂, NaKSO₄, NaNH₄HPO4 etc.

SALT HYDROLYSIS:

[1] ANIONIC SALT HYDROLYSIS:
[2] CATIONIC SALT HYDROLYSIS:
[3] CATIONIC AS WELL AS ANIONIC HYDROLYSIS:

[4] Amphoteric salt hydrolysis: