Chemistry > Ionic Equilibrium > 6.0 Salt Hydrolysis

  Ionic Equilibrium
    1.0 Reversible Reaction
    2.0 $pH$ Scale
    3.0 Arrehenius Theory of Electrolyte Ionization (Dissociation)
    4.0 Ionization of Water
    5.0 Determination of $pH$ of acids and bases
    6.0 Salt Hydrolysis
    7.0 Buffer Solution
    8.0 Solubility and Solubility Product

6.1 Salts of weak acid + strong base
A strong acid is defined as a substance which completely dissociates to give all the maximum possible ${H^ + }$,

For example: $$HCl{\text{ }} \to {\text{ }}{{\text{H}}^ + }{\text{ + C}}{{\text{l}}^ - }$$


Two cases arise:

a) When $\left[ {HCl} \right]{\text{ }} \geqslant {\text{ 1}}{{\text{0}}^{ - 6}}{\text{ M}}$, then contribution from the autoprotolysis of water is neglected in comparison to the ${H^ + }$ coming from the acid.

Therefore, $$\left[ {HCl} \right]{\text{ = }}\left[ {{{\text{H}}^ + }} \right]{\text{ }}$$


b) When $\left[ {HCl} \right]{\text{ < }}{10^{ - 6}}{\text{ M}}$ then contribution of ${H^ + }$ obtained from the autoprotolysis of water can't be neglected and needs to be included in the calculations.

But the contribution from water is not ${\text{ }}{10^{ - 7}}{\text{ M}}$ because it would give less than this amount in the presence of $HCl$.

This is because of common ion effect, which states that when a common ion is added to an equilibrium mixture, the equilibrium shifts in that direction where the common ion gets consumed.
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