Strong and weak Bases

 Hello! Welcome to today’s lesson. Today, we would consider the idea of strong and weak bases. We have previously considered the idea of strong and weak acids(see the page timeline). We said that a strong acid is an acid that dissociates completely in solution while a weak acid is an acid that does not dissociate completely in solution. We said that the percentage dissociation of a weak acid may be as low as 0.3% at about 1 M concentration of the solution. On the other hand, a strong acid may attain a 100% dissociation in solution.


A similar scenario applies to bases also. A strong base is a base that dissociates completely in solution. A weak base is a base that does not dissociate completely in solution.


When we talk about the dissociation of a specie, we are talking about the break up of the specie into its constituent ions.

Now consider the hypothetical base HB. The base would be dissociated as follows;

HB(aq)  --> H^+(aq) + B^-(aq)

This dissociation may also be called ionization(formation of ions).


Notice that I have used only the forward arrow in the reaction equation that have been written above. Generally, when the forward arrow is used in writing a chemical reaction equation, we are implying that the reaction goes on to completion. This therefore means that HB is a strong base. It ionizes or dissociates completely in solution to give H^+ and B^-.


In another instance, we could use the reversible arrow sign between the reactant and the products. In that case, we are implying that just as HB can be dissociated into H^+ and B^-, the ions could recombine to form HB again. The reaction is therefore reversible.

HB(aq) <-> H^+(aq) + B^-(aq)


In a situation where the rate at which HB dissociates to give H^+ and B^- is very slow, it then follows that the concentration of the ions H^+ and B^- in the system would be quite small hence the base ionizes only to a small extent and can therefore be regarded as a weak base.


Therefore, we come to the conclusion that in a weak base solution, there would be more unionized  HB molecules than the ions H^+ and B^-.




When we discussed about strong and weak acids, we introduced a constant that shows the extent of ionization of an acid called the acid dissociation constant Ka(refer to the page timeline Jun. 15 – 23, 2023). We shall again apply similar ideas to a weak base that dissociates in solution. I recommend that you review these earlier posts so as to aid your comprehension of tomorrow’s lesson. See you then!


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