Conductance

To find the ratio of molar conductivities, we start by using the relationship between molar conductivity ( ), specific conductivity ( ), and cell constant (G_cell):
, where is the molarity.
First, convert ppm to molarity. For KCl, 74.5 ppm = 74.5 mg/L = 0.0745 g/L.
Molarity of KCl ( ) for solution 1:

Similarly, for solution 2, 149 ppm = 149 mg/L = 0.149 g/L.
Molarity of KCl ( ) for solution 2:

Next, determine specific conductivity ( ):
, where is the resistance.
For solution 1,

For solution 2,

Calculate molar conductivities ( ):


The ratio
Thus, .
Verify if is within the range [1000, 1000]: it is.
The value of is 1000.

During the titration of a weak acid (benzoic acid) with a strong base (NaOH):
• Initially, the conductance is low because benzoic acid is a weak electrolyte and does not fully ionize in water.
• As NaOH is added, benzoic acid reacts to form the sodium benzoate salt, which is highly ionized, increasing the conductance.
• After the equivalence point, the excess NaOH contributes additional OH− ions, further increasing the conductance.
Option (2) represents this behavior correctly.

1. Analysis of the Graph:
The graph shows the molar conductance vs. for two electrolytes, A and B.
A exhibits a linear decrease in with , characteristic of a strong electrolyte.
B exhibits a sharp decrease, leveling off at higher concentrations, characteristic of a weak electrolyte.
2. Key Points to Identify the Incorrect Statements:
Statement 1: "Electrolyte A is a strong electrolyte because extrapolates linearly to ."

Statement 2: "Electrolyte B is a weak electrolyte, as does not extrapolate linearly to ."

Statement 3: "For strong electrolytes, decreases significantly with increasing ."

Statement 4: "Weak electrolytes exhibit a sharp decrease in at low concentrations due to incomplete dissociation."

3. Number of Incorrect Statements:
Only Statement 3 is incorrect. Statements A and C are correct.

Step 1: Analyzing Statement I
Mohr's salt is composed of three ions: ferrous , ammonium , and sulphate .
This statement is true because Mohr's salt (also known as ammonium ferrous sulphate) contains only these three types of ions.
Thus, Statement I is correct.
Step 2: Analyzing Statement II
The molar conductance of a salt at infinite dilution is the sum of the molar conductances of the ions it dissociates into. For Mohr's salt, the ions involved are:
Ferrous ion , with a molar conductance of , Ammonium ion , with a molar conductance of , Sulphate ion , with a molar conductance of . At infinite dilution, the total molar conductance of Mohr's salt should be the sum of the conductances of these ions. However, Statement II suggests the wrong coefficient for the sulphate ion. The sulphate ion is a monoatomic ion and should contribute to the total conductance, not .
Thus, the correct expression for the molar conductance should be:
Therefore, Statement II is incorrect because it incorrectly doubles the contribution of the sulphate ion.