JEE Challenger
More from Electrochemistry
ChemMedAdv 2011 • Paper 1

Conductometric Titration Plot of Silver Nitrate with Potassium Chloride

AgNO3 (aq.)\text{AgNO}_3\text{ (aq.)} was added to an aqueous KCl\text{KCl} solution gradually and the conductivity of the solution was measured. The plot of conductance (Λ)(\Lambda) versus the volume of AgNO3\text{AgNO}_3 is

Diagram 0

Options

A

(P\textbf{P})

B

(Q\textbf{Q})

C

(R\textbf{R})

D

(S\textbf{S})

Correct

Topics & Concepts

ElectrochemistryElectrochemical Cell

Step-by-Step Solution

To determine the variation of conductance (Λ\Lambda) of the solution as aqueous AgNO3\text{AgNO}_3 is added to an aqueous KCl\text{KCl} solution, we analyze the ionic species present in the solution at different stages of the titration:

  1. Before the equivalence point:
    The precipitation reaction that takes place is:
    Ag+(aq)+NO3−(aq)+K+(aq)+Cl−(aq)→AgCl(s)↓+K+(aq)+NO3−(aq)\text{Ag}^+ (\text{aq}) + \text{NO}_3^- (\text{aq}) + \text{K}^+ (\text{aq}) + \text{Cl}^- (\text{aq}) \rightarrow \text{AgCl} (\text{s})\downarrow + \text{K}^+ (\text{aq}) + \text{NO}_3^- (\text{aq})

    • K+\text{K}^+ ions act as spectator ions and remain in the solution.
    • For every Cl−\text{Cl}^- ion precipitated as insoluble AgCl\text{AgCl}, one NO3−\text{NO}_3^- ion is introduced into the solution.
    • The limiting molar ionic conductivities of Cl−\text{Cl}^- and NO3−\text{NO}_3^- are very close to each other:
      λ∘(Cl−)≈76.3 S⋅cm2mol−1andλ∘(NO3−)≈71.5 S⋅cm2mol−1\lambda^\circ(\text{Cl}^-) \approx 76.3\text{ S}\cdot\text{cm}^2\text{mol}^{-1} \quad \text{and} \quad \lambda^\circ(\text{NO}_3^-) \approx 71.5\text{ S}\cdot\text{cm}^2\text{mol}^{-1}
    • Since the mobility of the outgoing Cl−\text{Cl}^- ion is nearly identical to that of the incoming NO3−\text{NO}_3^- ion, the total conductance of the solution remains almost constant (represented by a nearly horizontal line).

  2. After the equivalence point:

    • All the Cl−\text{Cl}^- ions have completely reacted and precipitated as AgCl\text{AgCl}.
    • Subsequent addition of AgNO3\text{AgNO}_3 merely introduces additional Ag+\text{Ag}^+ and NO3−\text{NO}_3^- ions into the solution without any further precipitation.
    • The increase in the total concentration of ions causes the conductance to increase sharply and linearly with the volume of AgNO3\text{AgNO}_3 added.

Therefore, the conductance curve remains essentially flat up to the equivalence point and then increases steeply, which corresponds to graph (S).

Hence, the correct option is (D).

PreviousNext