Question

The correct order of conductivity of 0.001 (M) separate aqueous solutions of \([\text{Pt}(\text{NH}_3)_6]\text{Cl}_4\) (i); \([\text{Cr}(\text{NH}_3)_6]\text{Cl}_3\) (ii); \([\text{Co}(\text{NH}_3)_4\text{Cl}_2]\text{Cl}\) (iii) and \(\text{K}_2\text{PtCl}_6\) (iv) each containing octahedral complex species is

• A. (i) $<$ (ii) $<$ (iii) $<$ (iv)
• B. (i) $<$ (ii) $<$ (iv) $<$ (iii)
• C. (i) $<$ (iv) $<$ (iii) $<$ (ii)
• D. (iii) $<$ (iv) $<$ (ii) $<$ (i)

Hint:

In coordination chemistry, the electrical conductivity of aqueous solutions is a direct measure of the number of charges/ions. Count the species outside the coordination sphere plus the complex sphere itself to determine the total ion count.

Answer 1

The Correct Option is D

Step 1: Understanding the Concept:
The molar conductivity of an electrolytic solution at a given concentration depends primarily on the total number of ions produced per formula unit upon dissociation.
For coordination complexes, ions are produced from the species outside the square brackets (counter-ions) and the coordination sphere itself (which remains as a single charged complex ion).
Step 2: Detailed Explanation:
Let's determine the dissociation for each complex in aqueous solution:
1. (i) \([Pt(NH_3)_6]Cl_4\):
Dissociates as \([Pt(NH_3)_6]^{4+} + 4Cl^-\).
Total ions = \(1 (\text{complex}) + 4 (\text{chloride}) = 5\).
2. (ii) \([Cr(NH_3)_6]Cl_3\):
Dissociates as \([Cr(NH_3)_6]^{3+} + 3Cl^-\).
Total ions = \(1 (\text{complex}) + 3 (\text{chloride}) = 4\).
3. (iii) \([Co(NH_3)_4Cl_2]Cl\):
Dissociates as \([Co(NH_3)_4Cl_2]^+ + Cl^-\).
Total ions = \(1 (\text{complex}) + 1 (\text{chloride}) = 2\).
4. (iv) \(K_2PtCl_6\):
Dissociates as \(2K^+ + [PtCl_6]^{2-}\).
Total ions = \(2 (\text{potassium}) + 1 (\text{complex}) = 3\).
Comparing the ion counts:
(iii) produces 2 ions, (iv) produces 3 ions, (ii) produces 4 ions, and (i) produces 5 ions.
Molar conductivity increases as the number of ions per formula unit increases. Thus, the correct order is:
(iii) < (iv) < (ii) < (i).
Step 3: Final Answer:
The correct order of conductivity is (iii) < (iv) < (ii) < (i), which corresponds to option (D).