Question

Which one of the following has the highest molar conductivity?

• A. Diammine dichloroplatinum (II)
• B. Tetraamminedichlorocobalt (III) chloride
• C. Potassium hexacyano ferrate (II)
• D. Hexa aqua chromium (III) chloride

Hint:

Molar conductivity is related to the concentration of ions in the solution. Electrolytes that dissociate into a larger number of ions generally exhibit higher molar conductivity. Consider the formula of the complex to determine the number of ions it produces upon dissociation.

Answer 1

The Correct Option is C

Molar conductivity depends on the number of ions produced by one mole of the electrolyte in solution and the mobility of these ions.
Generally, an electrolyte that dissociates to produce a larger number of ions will have higher molar conductivity, provided the ions have reasonably high mobility.
Let's analyze the dissociation of each complex:
Option (A) Diammine dichloroplatinum (II): \( [Pt(NH_3)_2Cl_2] \) is a neutral complex and does not dissociate into ions in aqueous solution.
Its molar conductivity will be very low (close to zero).

Option (B) Tetraamminedichlorocobalt (III) chloride: \( [Co(NH_3)_4Cl_2]Cl \) dissociates into \( [Co(NH_3)_4Cl_2]^+ \) and \( Cl^- \) ions, producing 2 moles of ions per mole of the complex.

Option (C) Potassium hexacyano ferrate (II): \( K_4[Fe(CN)_6] \) dissociates into \( 4K^+ \) and \( [Fe(CN)_6]^{4-} \) ions, producing 5 moles of ions per mole of the complex.
The high charge of the complex ion also contributes to significant ionic strength and conductivity.

Option (D) Hexa aqua chromium (III) chloride: \( [Cr(H_2O)_6]Cl_3 \) dissociates into \( [Cr(H_2O)_6]^{3+} \) and \( 3Cl^- \) ions, producing 4 moles of ions per mole of the complex.
The \( Cr^{3+} \) ion is also highly charged, contributing to conductivity.
Comparing the number of ions produced per mole of the electrolyte:
Option (A) 0 ions
Option (B) 2 ions
Option (C) 5 ions
Option (D) 4 ions Potassium hexacyano ferrate (II) produces the highest number of ions per mole (5 ions: 4 \( K^+ \) and 1 \( [Fe(CN)_6]^{4-} \)), which would lead to the highest molar conductivity among the given options, assuming reasonable ionic mobility.