Question

Consider the statements S1 and S2:
S1: Conductivity always increases with decrease in the concentration of electrolyte.
S2: Molar conductivity always increases with decrease in concentration of electrolyte.

The correct option among following is:
A. Both S1 and S2 are correct
B. S1 is wrong and S2 is correct
C. S1 is correct and S2 is wrong
D. Both S1 and S2 are wrong

Answer 1

. The compound which can dissociate itself completely will be the best conductor of electricity as the ions are mobile and lead to the flow of current which is nothing but electricity. So the compound that gives maximum ions is most conductive.

Complete step by step answer:
-Based on the property of the compounds being able to dissociate into their ions, they are classified in 2 groups- electrolytes and non-electrolytes. Electrolytes are further classified as strong and weak electrolytes.
-Electrolyte is a compound which dissociates into its constituent ions, cation and anion in presence of DC current under the process of electrolysis.
-Many types of compound can be used as electrolytes but the most preferred compounds are acids, bases and salts.

-Acids are the compounds that donate ${{H}^{+}}$ ion to become anion. Bases are compounds that accept the ${{H}^{+}}$ ion and convert into cation. Salts are the compounds formed mainly by the reaction of acids and bases.

-Electrolytes dissolve in water to form a solution and that solution conducts electricity by dissociating into ions.
Eg. $NaCl\left( s \right)\to N{{a}^{+}}\left( aq \right)+C{{l}^{-}}\left( aq \right)$
Water is added as solvent so that the ions can become mobile. Only then they can conduct electricity.

-Strong electrolytes are those which can dissociate to a very large extent to give the respective cations and anions. Weak electrolytes are those which dissociate very less and so the ions formed are not much which reduces the conductivity of the solution.

-Dissociation of strong electrolytes is shown by a forward arrow and that of weak electrolytes is shown by double arrows.
$NaCl\left( s \right)\to N{{a}^{+}}\left( aq \right)+C{{l}^{-}}\left( aq \right)$
It signifies that this electrolyte is a strong electrolyte.
${{H}_{2}}O\rightleftarrows {{H}^{+}}+O{{H}^{-}}$
It signifies that water is a weak electrolyte.

-Some examples of acids as strong electrolytes are HCl, HBr, HI, $HCl{{O}_{4}},{{H}_{2}}S{{O}_{4}}$ and acids as weak electrolytes are $C{{H}_{3}}COOH,HF,{{H}_{2}}C{{O}_{3}},{{H}_{3}}P{{O}_{4}}$
-Some examples of bases as strong electrolytes are NaOH, KOH, LiOH, $Ca{{\left( OH \right)}_{2}}$ and bases as weak electrolytes are ammonia, pyridine.
-Some examples of salts as strong electrolytes are NaCl, KCl, $N{{H}_{4}}Cl$ and salts which are weak electrolytes are AgCl, $PbC{{l}_{2}}$

-If the concentration of electrolytes is decreased, then there will be less dissociation of the electrolytes into the ions and so the conductivity will reduce and not increase. So S1 is wrong.

-The formula for molar conductivity is given as
${{\Lambda }_{M}}=\dfrac{1000 X k}{C}$
Here, k is the dissociation constant and C is the concentration of the electrolyte. Both C and k decreases on reducing the concentration of the electrolyte through dilution but the effect of C is more as it is directly affecting the dissociation of the electrolytes and so the overall conductivity increases and the statement is correct.
So, the correct answer is “Option B”.

Note: Always the effect of the overall equation is considered when more than 1 factors are responsible for a given characteristic. Compounds which do not dissociate at all into its cation and anion are termed as non-electrolytes. They are different from electrolytes as they do not conduct electricity when placed in a galvanic cell while electrolytes conduct electricity.