Question

Using acid dissociation constants below, which substance is the strongest base?

Substance	${{k}_{a}}$
Hydrogen carbonate ion (bicarbonate ion) $HCO_{3}^{-}$	$4.8\times {{10}^{-11}}$
Hydrogen Phosphate ion $HPO_{4}^{-}$	$3.6\times {{10}^{-13}}$
Water ${{H}_{2}}O$	$1.0\times {{10}^{-14}}$
Hydrogen Sulfide ion $H{{S}^{-}}$	$1.0\times {{10}^{-19}}$

(A) $CO_{3}^{2-}$
(B) $PO_{4}^{3-}$
(C) $O{{H}^{-}}$
(D) ${{S}^{2-}}$

Answer 1

We know that the principle of interaction of ions of salt thereupon of water is called salt hydrolysis. Weak electrolyte (weak acid and weak base) is dissociated to a little extent in solution and there’s an equilibrium between the undissociated electrolyte and therefore ions formed in solution.

Complete answer:
Salt Hydrolysis definition chemistry is neutralization reaction between an acid and base results in the formation of salt. Most salts ionize in water to form acids and bases. These salts dissociate into their respective ions, which exist as hydrated ions in aqueous solutions or can interact with the hydrogen or hydroxyl ion of the solvent to form the resulting bases and acids. The mechanism of interaction between the ions of the salts with that of water is called hydrolysis of salts. Salts of a weak acid and base: Salts resulting from the neutralization reaction between a weak and weak base are often mildly basic, mildly acidic, or neutral counting on the nature of the bases and acids involved. The degree of hydrolysis and ionization of water is independent of the concentration of the solution.
The salts that are produced by the reaction between a strong base and a strong acid are neutral in nature. The bonds formed between the anion and the cation are strong, and they do not break apart in solution. The electronic distribution of both the cation and the anion after the formation of the bond between them is such that both the ions complete their most stable electronic configuration.
A strong base is one which has a higher value of ${{K}_{b}}.$ Since product of ${{K}_{a}}$ ​ and ${{K}_{b}}$ ​ is constant, higher value of ${{K}_{b}}$ ​corresponds to lower value of ${{K}_{a}}.$ Hence, a strong base has a lower value of ${{K}_{a}}.$ Also, weaker the acid, stronger is its conjugate base. From the given data, $H{{S}^{-~}}$ is the weakest acid having least value of ${{K}_{a}}.$ Hence, its conjugate base ${{S}^{2-}}~$ is the strongest.
Therefore, the correct answer is option D.

Note:
Remember that salt of a weak acid and weak base undergoes both cationic and anionic hydrolysis. In cationic hydrolysis it gives a weak base and in anionic hydrolysis it gives a weak acid. The ionization constant may be a measure of acid strength; the higher the value, the greater the number of hydrogen ions liberated per mole of acid in solution and therefore the stronger the acid is.