The concept of salt water hydrolysis

Salt is a strong electrolyte and dissociates completely in water
.
Some salt solutions are neutral, while others are acidic or alkaline.

For example, sodium acetate, NaAc completely dissociate in water generation of Na ⁺ and Ac ^- , Ac ^- and solution H ⁺ binding HAc generate weak electrolyte, and maintain balance

The relationship between the concentration of H ⁺ , Ac ^- and HAc in the solution and the equilibrium constant is

In NaAc solution, H ⁺ comes from the dissociation equilibrium of H ₂ O

The concentration of H ⁺ in the solution decreases due to the formation of HAc, and the dissociation equilibrium of H ₂ O shifts to the direction of generation of H ⁺ , which increases the concentration of OH ^- in the system
.
Therefore, the OH ^- concentration in the solution is higher than the H ⁺ concentration, and it is alkaline

NaAc is a salt produced by weak acid and strong base.
This kind of salt is called weak acid and strong base salt, and its aqueous solution is alkaline; the salt obtained by the action of weak base and strong acid is called weak base strong acid salt, such as NH ₄ Cl.
The aqueous solution is acidic due to the formation of weak electrolytes NH ₃ and H ⁺ due to the hydrolysis of NH ₄ ⁺ ; NH ₄ Ac and NH ₄ HCO ₃ are weak acid and weak alkaline salts.
The positive and negative ions dissociated from the salt in the aqueous solution are both hydrolyzed (double hydrolysis).

The positive and negative ions generated by the dissociation of strong acid and strong base salt do not interact with the H ⁺ and OH ^- in the system to generate weak electrolytes, and do not undergo hydrolysis, so the aqueous solution is neutral

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