Ionic equilibrium- Definition and calculations

Published by Daniel Ozori on

Hey there!…. before we start this article on “ionic equilibrium” i would just like to refresh your memory on just what an ion is.

Ions are charged particles of atoms which are created when a certain atom loses or gains extra electrons to attain a net negative or positive charge.

All caught up?….if you don’t still understand what an ion is, or you just want more details on it, use the link to refer to my article explaining what ions are: “Atoms, ions and molecules”

OK back to our topic at hand, what’s ionic equilibrium?

Ionic equilibrium– Definition

In a chemical reaction, chemical equilibrium is a state in which the reactants and the products of the reaction are exactly the same with no change in the chemical constituents.

Just imagine an ice block melting into liquid water,

example of chemical equilibrium

the amount of frozen water contained in the block is the same as the amount of liquid water contained after melting so there’s no actual change in the constituents during the process.
well that’s kinda how chemical equilibrium is, there’s no net change in the process of the reaction allowing it to achieve an equilibrium.

But even though there’s an equilibrium, it does not mean that the reaction has stopped, the reaction is still going on.

Ionic equilibrium in particular involves the equilibrium of the unionized molecules and the ions in a solution of weak electrolytes.

Electrolytes are substances that can conduct electricity in their molten state

when a particular substance is added to a solvent with a good amount of heat, the substance dissociates into ions which are then free to move around in the solvent.

And after this reaction has taken place the process can still be reversible.

for example, take acetic acid (a weak acid) breaking up into acetate ions and hydrogen ions in water:

CH3 COOH ⇌  CH3 COO- + H+

looking at the example it’s shown clearly that the acetic ion did not dissociate completely.

Instead, it splits itself into two ions, one positive and another negative with the equilibrium  symbol () showing that the reaction is a reversible one.

The acetic acid is able to split itself into two ions mainly because it is a weak acid, and there are electronegativity differences of oxygen and hydrogen in -OH group of acetic acid upon addition of water.

Dissociation constant of acids and bases

Another important thing to understand in ionic equilibrium is how calculate the dissociation constant of acids and bases into ions.

Which is very easy to do when you understand it properly so lets get right on it.

Dissociation like said earlier is the ability for molecules to split itself into smaller ions,strong acids and bases dissociate very well almost completely while weak acids like the acetic acid on the hand don’t dissociate so well.

Dissociation constant tells us the amount of dissociated ions to the original acid or base.

For acids it is abbreviated as Ka where K stands for a constant termed Arrhenius constant and a stands for the acid.

While bases are represented as Kb 

A high Ka or Kb value means that the acids dissociates very well and is a strong acid or base, A low one would mean it dissociates poorly and is a weak acid or base.

An example of this is hydrochloric acid in water dissociating to yield Hydrodium and Chlorine ions.

HCL + H2O ⇌ H3O++ Cl-

The positive product (ion) H3O is known as the conjugate acid and the negative product (ion) Cl is known as the conjugate base.

It goes like this;

Substance + H2O ⇌ H-subtance+ + OH-






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