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Salt Hydrolysis is the process of the formation of salt by the neutralization reaction between a base and acid. Salts are formed in definite amounts and go through ionization in water. Ionization of salts results in the formation of cations or anions. It exists by interacting with water to form alike acids and bases depending on the nature of the salt or exists in the form of hydrated ions in a saturated solution.
Read more: Types of solutions
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Key terms: Salt, hydrolysis, reaction, water, acid, base, basic, solution, acidic, ions, cation, anion
Salt hydrolysis
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Cations and anions as a result of salt ionization either exist as hydrated ions in an aqueous solution or give rise to bases and acids by coming in contact with the hydroxyl or hydrogen ion of the solvent. The process of reaction between the ions of salt and water is known as the hydrolysis of salt. Salts can be of various types based on the types of hydrolysis. The different types of salts are:
- Acidic salt
- Basic salt
- Neutral or amphoteric salt
Types of Salt Hydrolysis
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The different types of of salt hydrolysis are as follows:
Salts of a strong base and strong acid
Salts which are produced by such reactions are neutral in nature. There exists a strong bond between the cations and the anions. Both ions complete their most stable electronic configuration in the distribution of the electrons after the formation of the bond. The bonds of the salts are ionic or electrostatic. The salts can get hydrated rather than getting hydrolyzed. These salts are also known as neutral or amphoteric salt because they do not carry any charge.
Example: Sodium chloride
Salts of a weak acid and a strong base
Positively charged salts are formed as a result of a strong base and a weak acid. Such salts are also known as basic salt because they hydrolyze easily in water.
Example: sodium acetate
The salt hydrolysis formula is:
| CH3COONa (aq) → CH3COO- + Na+ (aq) |
Acetic acid and hydroxyl ion is formed when the acetate ion reacts with hydrogen ion in water
| CH3COO- (aq) + HOH → CH3COOH + OH- (aq) |
Acetic acid does not get ionized in water because it is a weak acid but the basicity of the solution is increased because of the increase in the OH – ions. The pH level of the saturated solutions of these salts is always more than 7 which is why these salts are called a basic salt.
Salts of a weak base and a strong acid
These salts are acidic in nature.
Example: Ammonium chloride
| NH4Cl(aq) → Cl−(aq) + NH4+(aq) |
Ammonium hydroxide is formed when ammonium ions react with hydroxyl ions in the water molecules. The aqueous solution of these salts has a pH of less than 7 and is acidic in nature because of the hydrogen ions.
| NH+4(aq) + H2O ⇋ NH4OH(aq) + H+(aq) |
Salts of a weak base and a weak acid
Salts formed by the reaction/neutralization between a weak base and a weak acid can be mildly acidic, mildly basic, or neural based on the type of acids and bases involved. The concentration of the solution determines the degrees of ionization and hydrolysis of water.
Example: CH3COONH4
The formula is :
| CH3COO− + NH+4 + H2O ⇋ CH3COOH + NH4OH |
Things to remember
- Salt hydrolysis is the reverse of neutralization.
- NaCl and KCl are examples of salts formed by the neutralization of a strong acid and a strong base
- Salts of strong acid and a strong base do not go through hydrolysis
- Sodium sulfate is a salt of strong acid and a strong base that does not undergo hydrolysis in water
- Na2CO3 undergoes anionic hydrolysis
Sample questions
Ques. What is the difference between cationic and anionic hydrolysis (4 marks)
Ans.
| Cationic hydrolysis | Anionic hydrolysis |
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Ques. Give an example of a salt that will give the highest PH in water (3 marks)
Ans. Na2CO3 is the basic due to hydrolysis of CO2-3 ion
It is basic in nature because of the hydrolysis of CO2-3 ion
CO32- + H2O ⇌ HCO3- + OH-
Thus, Na2CO3 is a salt that will give the highest PH in water
Ques. Give an example of a salt that will give a basic solution in hydrolysis. (2 marks)
Ans. KCN is a kind of salt that is basic in nature as it is made of a strong base and a weak acid.
KCN → K+ + CN-
CN- + H2O → HCN + OH-
Ques. Why is the aqueous solution of sodium cyanide basic in nature? (3 marks)
Ans. The hydrolysis of cyanide ions is the reason behind the basic nature of the aqueous solution of sodium cyanide. The basic nature of the solution is due to the production of OH – ions as a result of the hydrolysis of the cyanide ion.
The dissociation reaction of NaCN :
NaCN →Na+ + CN-
The hydrolysis of cyanide ions is:
CN- + H2O → HCN + OH-
Ques. What is the difference between the three kinds of salt? (5 marks)
Ans.
| Basic salt | Neutral salt | Acidic salt |
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Ques. What is hydrolysis? (2 marks)
Ans. Hydrolysis is the process in which water molecules break into two parts of the molecule. H+ ion and OH- ion will be divided among the two molecules of a substance. The hydrolysis reaction is used mainly to break polymers into monomers.
General formula :
AB + H2O → AH + BOH
Ques. What are the different types of hydrolysis? What is salt hydrolysis? (2 marks)
Ans. The different types of hydrolysis are:
- Salt
- Acids and bases
- ATP
When salt reacts with water as the cations and anions of salt and water interact with each other, it is known as salt hydrolysis. Salt breaks down into ions during the process of hydrolysis.
Ques. Show the hydrolysis reaction for magnesium nitrate (2 marks)
Ans. The hydrolysis reaction for magnesium nitrate is:
Mg3N2 + 6H2O → 3Mg (OH)2 + 2NH3
Ques. What are the basic salts? (1 mark)
Ans. The salts formed from the neutralization reaction between a strong base and weak acid are basic salts. The pH of an aqueous solution of such salt is more than 7.
Ques. What are Acidic Salts? (1 mark)
Ans. The salts formed from the neutralization reaction between a strong acid and a weak base are acidic salt. The pH of an aqueous solution of such salt is less than 7.
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