Question

Review the equilibrium and choose the correct statement \[HCl{{O}_{4}}+\text{ }{{H}_{2}}O~\underset{{}}{\leftrightarrows}{{H}_{3}}{{O}^{+}}+\text{ }Cl{{O}^{-}}_{4}\]
A. $\text{ }HCl{{O}_{4}}is\text{ }the\text{ }conjugate\text{ }acid\text{ }of\text{ }{{H}_{2}}O \\$
B. $\text{ }{{H}_{3}}{{O}^{+}}is\text{ }the\text{ }conjugate\text{ }base\text{ }of\text{ }{{H}_{2}}O \\$
C. $\text{ }{{H}_{2}}O\text{ }is\text{ }the\text{ }conjugate\text{ }base\text{ }of\text{ }{{H}_{3}}{{O}^{+}} \\$
D. $\text{ }Cl{{O}^{-}}_{4}is\text{ }the\text{ }conjugate\text{ }base\text{ }of\text{ }HCl{{O}_{4}} \\$

Answer 1

Hint: As an acid loses a proton (\[{{H}^{+}}\]) as per its definition give a compound which has the tendency to accept same proton (\[{{H}^{+}}\]), this compound is known as conjugate base of initial acid. Also a base accept a proton (\[{{H}^{+}}\]) as per its definition and change to compound which has tendency to lose proton (\[{{H}^{+}}\]), this compound is known as conjugate acid of initial base such as
Acid + Base \[\underset{{}}{\overset{{}}{\longleftrightarrow}}\] Conjugate base + Conjugate acid

Complete Step by Step Solution:
In a given chemical equation, \[HCl{{O}_{4}}\]is an acid and thus, water behaves as base (amphoteric in nature). HClO4 will release a proton (\[{{H}^{+}}\]) in the presence of base and changed to \[Cl{{O}_{4}}^{-}\](anion). Now \[Cl{{O}_{4}}^{-}\] (anion) has a tendency to accept a proton to get neutral and stable thus, behave as a base. And this base (\[Cl{{O}_{4}}^{-}\]) is known as conjugate base of given acid (\[HCl{{O}_{4}}\]) such as
\[HCl{{O}_{4}}+{{H}_{2}}O\underset{{}}{\leftrightarrows}{{H}_{3}}{{O}^{+}}+Cl{{O}_{4}}^{-}\]

On the other side, water, H2O which is amphoteric in nature, will behave as base in the presence of given acid. Water as base will accept proton released by acid (\[HCl{{O}_{4}}\]) and change to a cation,\[{{H}_{3}}{{O}^{+}}\]. Now this cation has a tendency to lose protons to get neutralised and stable thus, will behave as acid. And this acid is known as conjugate acid of given base (\[{{H}_{2}}O\]) such as
\[HCl{{O}_{4}}+{{H}_{2}}O\underset{{}}{\leftrightarrows}{{H}_{3}}{{O}^{+}}+Cl{{O}_{4}}^{-}\]

Thus, from all the three options, the correct option is D.

Note: It is important to note that, a strong acid will give weak conjugate base and weak acid will give strong conjugate base. Similarly, strong base will give weak conjugate acid and weak base will give strong conjugate acid. An acid is a substance which loses protons in an aqueous solution and a base is a substance which accepts the same proton as per Bronsted Lowry theory regarding acid and base. Water is amphoteric in nature, behaves as acid in the presence of base and will behave as base in the presence of acid.