Saline hydrolysis of weak acid and strong base

When preparing an aqueous solution of NaCN (sodium cyanide), we find that its pH is greater than 7, therefore it constitutes a strong base. Follow the hydrolysis analysis of this salt:

When adding NaCN base in a neutral medium (water), it makes the solution basic (pH > 7).
The classic equation of the process is:


The products of the reaction are:
NaOH (sodium hydroxide): strong base
HCN (hydrocyanic acid): weak acid
The following two rules are useful for obtaining the equation of the salt hydrolysis process:
1. Dissociate the salt (separate the cation from the anion)
2. Dissociate the strong base (COH → C+ +OH-)

• NaCN, being a soluble salt, is dissociated:
NaCN → Na+ + CN-
• NaOH, as it is a strong base, is dissociated:
NaOH → Na+ + OH-
Thus, the most correct way to represent the reaction is:


CN- (aq) + H2O(l) ↔ OH- (aq) +HCN(aq)
Note that the hydrolysis (breaking the molecule through water) was the CN- anion, that is, the ion coming from the weak acid.
Generic equation of anion hydrolysis: THE- + HOH → HA + OH-


Conclusion: weak acid salt and strong base give the solution basic character (pH > 7). The presence of the OH- ion justifies the basic medium.

By Líria Alves
Graduated in Chemistry
Brazil School Team

See more!
Salt hydrolysis of strong acid and weak base
saline hydrolysis

Physicochemical - Chemistry - Brazil School

Source: Brazil School - https://brasilescola.uol.com.br/quimica/hidrolise-salina-acido-fraco-base-forte.htm

3 practical recipes for those who live alone

The life of those who live alone and need to work or study is not easy, so many resort to ready-m...

read more

Learn how to find out the size of the dog by the paw

Certainly, the height that dogs reach depends on some factors, mainly the breed, so it is common ...

read more
What's different about these images? must find!

What's different about these images? must find!

In recent times, the number of challenges of attention, spot the difference and optical illusions...

read more