Various Types of Salt Hydrolysis
If viewed from the components of the salt and the amount of salt can be described when reacted with water, the hydrolysis reaction can be distinguished as follows.
1. Partial hydrolysis
Partial hydrolysis is when a salt is reacted with water, only one / a portion of the ions will undergo a hydrolysis reaction, while others do not. The components of salt that undergo a partial hydrolysis reaction are weak acids and strong bases or vice versa.
2. Total hydrolysis
Total hydrolysis is the reaction of decomposition of all salt by water, which component of salt consists of weak acids and weak bases.
Based on the types of ions produced when salt dissolves in water, the hydrolysis process can be divided into the following types.
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3. Anion hydrolysis
If a salt consisting of a component of a weak acid molecule and a strong base is reacted with a water molecule, then these salts will only be partially hydrolyzed in water and will produce alkaline ions (OH-). In other words, what is hydrolyzed is that the anion is from a weak acid while the cation from a strong base is not hydrolyzed.
Example:
CH3COONa (aq) → CH3COO– (aq) + Na + (aq)
CH3COO– + H2O ↔ CH3COOH + OH–
Na ++ H2O → no reaction occurs
From the example above, it is explained that CH3COO - which acts as a hydrolyzed weak acid anion to form OH - when reacted with a water molecule (H2O) while Na + which acts as a cation of a strong base is not hydrolyzed when reacted with a water molecule.
In conclusion, salt with weak acid and strong base forming components, if reacted with water, will partially hydrolyze and produce alkaline ions.
4. Cation hydrolysis
Similar to the hydrolysis reaction between salt with components of weak acid molecules and strong bases reacted with water molecules, if salt with components of strong acids and weak bases is dissolved into water molecules will also undergo partial hydrolysis and produce ions that are acidic (H +). This happens because only the cation of a weak base is hydrolyzed, whereas the anion of a strong acid does not undergo hydrolysis.
Example:
NH4Cl → NH4 + + Cl–
NH4 + + H2O ↔ NH4OH + H +
Cl– + H2O → no reaction occurs
Based on the example above, it can be explained that NH4 + which acts as a weak hydrolyzed base produces an acidic ion, namely H +. Whereas Cl-which as a strong acid anion is not hydrolyzed.
5. Hydrolyzed Cations and Anions
If a salt with a weak acid component and a weak base is reacted with a water molecule it will undergo total hydrolysis. This can occur because the cation of a weak base or anion of a weak acid can be completely hydrolyzed. This hydrolysis reaction produces H + or OH- ions.
Example:
CH3COONH4 → CH3COO– + NH4 +
CH3COO– + H2O ↔ CH3COOH + OH–
NH4 + + H2O ↔ NH4OH + H +
The example above, explains that the two constituent components of CH3COO- salt (anion from weak acids) and NH4 + (cations from weak bases) can be completely hydrolyzed, each of which sequentially produces ions that are basic (OH-) and ions that are acidic (H + ).