Question

Identify the weak electrolyte from the following:
(A) Sodium chloride solution
(B) Dilute hydrochloric acid
(C) Dilute sulphuric acid
(D) Aqueous acetic acid

Answer 1

Hint: Weak electrolytes are those electrolytes which cannot be completely ionised and so their electrical conductivity is very low. They are usually weak acids and weak bases.

Complete step by step answer:
- First let us see what an electrolyte is.
Any substance which when dissolved in water or some other polar solvent makes the solution electrically conducting. The electrical conductivity is due to the cations and anions dispersed in the solution after dissociation of electrolyte.
The formed solution is electrical neutral, but when an electrode potential is applied to it the cations and anions will move toward the oppositely charged electrodes. This movement of ions is the flow of current. The electrolytes can be some acid, base or even salt.
-Based on their degree of dissociation and ability to conduct electricity the electrolytes are of 2 types:
 (1)Strong electrolytes
 (2)Weak electrolytes
-Strong electrolytes: These electrolytes are the ones which can be completely ionized (100%) and thus conduct electricity when dissolved in water or a polar solvent. Their extent of ionisation is more than weak electrolytes and they do not obey the Ostwald’s dilution law.
Strong electrolytes can be strong acids, bases or salts. For example:
- Strong acids like: HCl, HBr, $HN{O_3}$, ${H_2}S{O_4}$, $HCl{O_3}$, $HCl{O_4}$, etc.
- Strong bases like: NaOH, LiOH, KOH, $Ca{(OH)_2}$, etc.
- Salts like: NaCl, $MgC{l_2}$, KBr, etc.
-Weak electrolytes: These are those electrolytes which are only partially ionised (about 1-10%), which means it can be ionised to a very small extent and thus lesser than strong electrolytes. Their electrical conductivity is very low or almost negligible. Also Ostwald’s dilution law is applicable for them.
Weak electrolytes can be weak acids and weak bases. For example:
- Weak acids like: HF, ${H_2}C{O_3}$, ${H_3}P{O_4}$, $C{H_3}COOH$ etc.
- Weak bases like: $N{H_3}$, ${C_5}{H_5}N$, etc.
-So, we now know that sodium chloride solution, dilute Hydrochloric acid and dilute sulphuric acid will form strong electrolytes because they are salts and strong acids. While dilute acetic acid being a weak acid will form a weak electrolyte.

The correct option will be: (D) Aqueous acetic acid.

Note: The Ostwald’s dilution law is usually applicable for weak electrolytes. This Law describes the dissociation constant of the weak electrolytes with the degree of dissociation (α) and the concentration of the weak electrolyte.
$\alpha = \sqrt {\frac{K}{C}} $
Where, K = dissociation constant of weak electrolyte, C = concentration and α = degree of dissociation.