Why chloride is a weak base

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Acids and bases can cancel each other's properties. For example, if you mix equal amounts of hydrochloric acid and sodium hydroxide solution, you get a saline solution with a pH of 7.

The protons of the acid are absorbed by the base. This process is called neutralization.Note: When using the notation above, it should not be forgotten that the reaction partners are present in solution as hydrated ions, as is clear from the notation as an ion reaction, for example.

The sodium ion and the chloride ion are not affected by the reaction, but remain in the solution as hydrated ions. The actual neutralization reaction consists in the formation of water from hydronium and hydroxide ions.

The reaction releases heat, the enthalpy of reaction is negative. In this reaction it is called the heat of neutralization.

If, instead of a strong acid, a weak acid is neutralized with sodium hydroxide solution, the solution does not have a neutral pH value, but has a basic reaction. This will be discussed using the example of acetic acid.

If you add the same amount of substance to an acetic acid solution with n acetic acid molecules (total amount, i.e. dissociated and non-dissociated form), these react completely to form acetate and water. However, an acetate solution is in equilibrium with its conjugate acid:

+ ⇄ +

The weak base acetate reacts to a small but no longer negligible proportion with water. Ions are formed and this increases a little. If one were to dissolve a salt of a weak acid such as sodium acetate () directly, the same value would result. If weak bases are neutralized with a strong acid, the value falls accordingly below the value of 7.

Tab. 1
HAB.resulting pHExamples
strongstrong≈ 7 and strong base
weakstrong> 7 and strong base
strongweak< 7 and strong acid

If you neutralize acids or bases, a neutral value does not necessarily result. Neutralization simply means that equimolar amounts of acid and base are reacted.