Question

The dissociation constants of acids $\text{HA}$, $\text{HB}$, $\text{HC}$ and $\text{HD}$ are \[2\cdot 6\times {{10}^{-3}}\], \[5\cdot 3\times {{10}^{-9}}\], \[1\cdot 1\times {{10}^{-2}}\] and \[7\cdot 5\times {{10}^{-5}}\] respectively. The weakest acid amongst these acids is:
(A) $\text{HA}$
(B) $\text{HB}$
(C) $\text{HC}$
(D) $\text{HD}$

Answer 1

Hint: The acid dissociation constant \[{{K}_{a}}\] is a quantitative measure of the strength of an acid in solution. Higher the dissociation constant, stronger is the acid. A strong acid dissociates or basically ionizes almost completely in water. The dissociation constant can determine whether the acid is weak or strong.

Complete Step by Step solution:
Given, Dissociation constant of HA\[=2\cdot 6\times {{10}^{-3}}\]
Dissociation constant of HB\[=5\cdot 3\times {{10}^{-9}}\]
Dissociation constant of HC\[\text{=}1\cdot 1\times {{10}^{-2}}\]
Dissociation constant of HD\[\text{=}7\cdot 5\times {{10}^{-5}}\]
The dissociation constant measures the strength of an acid, so the acid with lowest dissociation constant will be the weakest. From the above given acids, acid HC has the lowest dissociation constant. So, it is the weakest acid.

So, the answer is option-(C).

Additional Information: The dissociation constant is represented by\[{{K}_{a}}\]. The higher the \[{{K}_{a}}\] value, the greater the no. of hydrogen ions liberated per mole of acid in the solution and hence stronger is the acid. Low values of \[{{K}_{a}}\] mean that the acid does not dissociate well and that it is a weak acid.
We can also say that, the more easily the acid dissociates and the stronger it is i.e. the weaker the base it is, and the less strongly its bonds are held together by electron donation. Acid dissociates into \[{{H}^{+}}\] and an anion, bases dissociates into \[O{{H}^{-}}\] and a cation.
Dissociation: Atoms can gain or lose electrons in order to form ions in a process called ionization. When ionic compounds dissolve in water their ions separate from one another in a process called dissociation.
The world’s strongest acid is at least a million times more potent then concentrated sulfuric acid has been made in a lab in California. Its name is Carbonate Acid.
A weak acid is an acid that partially dissociates into ions in an aqueous solution or water whereas, the strong acid fully dissociates into ions in water. The conjugate base of a weak acid is a weak base, while the conjugate of a weak base is a weak acid.
Ex- Acetic acid is a Weak Acid.

Note: Study the concepts of Dissociation Constants for acids and bases, the Examples of strong and weak acids and the properties that differentiate them. The extent to which they dissociate in various solutions, one can also study about the \[p{{K}_{a}}\] value which is given by the negative log of \[{{K}_{a}}\] values. The higher the \[p{{K}_{a}}\] value, the weaker the acid is.