The Question is from neet-chemistry coordination-compounds , and it was created by the author A.RAMA NAGESWARARAO

Question

A cobalt complex [Co(NH3)xCl2]Cl has a molar conductivity corresponding to a 1:1 electrolyte.  It exhibits cis-trans isomerism but no optical activity.  What is the likely value of x and geometry?

A.RAMA NAGESWARARAO · Accepted Answer

## CORE INFORMATION
✓ **Answer**: C
## CONCEPT FRAMEWORK
	**Primary Concept**: Coordination Chemistry, Isomerism, Conductivity of Electrolytes
	**Related Topics**: Werner's Theory, Coordination Number, Geometry of Complexes
	**Prerequisites**: Basic understanding of complex ions, isomerism, and conductivity.
## SOLUTION PATHWAY
**Given Information**:
	1. The complex is [Co(NH3)xCl2]Cl. This indicates one chloride ion outside the coordination sphere.
	2. It's a 1:1 electrolyte, meaning it dissociates into two ions: [Co(NH3)xCl2]+ and Cl–.
	3. It exhibits cis-trans isomerism.
	4. It has no optical activity.
**Method & Steps**:
	1. **Determine the Coordination Number**: Since the complex has a 1:1 electrolyte behavior, the coordination sphere contains cobalt, x NH3 molecules, and 2 Cl– ions. The overall charge of the coordination sphere is +1 to balance the outer Cl–.  This implies the cobalt likely has a +3 oxidation state (common for cobalt), and the coordination number is x + 2.
	2. **Analyze for Cis-Trans Isomerism**:  Cis-trans isomerism is commonly observed in square planar (Coordination Number = 4) and octahedral (Coordination Number = 6) complexes. Tetrahedral complexes rarely show cis-trans isomerism.
	3. **Consider Optical Activity**: The absence of optical activity suggests the complex has a plane of symmetry.  A cis isomer of a square planar complex with two different ligands would be optically active. However, trans isomers always have a plane of symmetry and thus no optical activity. Similarly, trans isomers of octahedral complexes [MA4B2] are not optically active.
	4. **Deduce x and Geometry**: Combining the information, a coordination number of 6 (octahedral) with a trans-[Co(NH3)4Cl2]+ complex fits all the criteria. This means x = 4.
**Result**:
	x = 4, Octahedral Geometry
**Verification**: A complex with formula [Co(NH3)4Cl2]Cl, where the coordination sphere is [Co(NH3)4Cl2]+, satisfies the 1:1 electrolyte behavior. The trans isomer of this octahedral complex shows cis-trans isomerism but no optical activity.
## OPTION ANALYSIS
[A] x = 2, tetrahedral :x: A tetrahedral complex with two different ligands would not readily exhibit cis-trans isomerism.  Also, the coordination number would be 4, not consistent with the conductivity data.
[B] x = 4, square planar :x: A square planar complex [Co(NH3)4]2+ would not match the formula given, as it wouldn't accommodate the two chloride ligands within the coordination sphere. Moreover, a cis-square planar complex of [MA2B2] type would be optically active.
[C] x = 4, octahedral ✓: This option satisfies all the given conditions.
[D] x = 6, octahedral :x: If x = 6, the complex would be [Co(NH3)6Cl2]Cl. This would not be a 1:1 electrolyte, and the formula would suggest a coordination number of 8 which is less common for Co(III).
## LEARNING AIDS
	**Common Mistakes**:
		1. Incorrectly interpreting the conductivity data: Ensure you understand how conductivity relates to the number of ions formed upon dissociation.
		2. Confusing cis-trans and optical isomerism: Remember that not all cis isomers are optically active, and not all optically active complexes are cis isomers.
	**Quick Tips**:
		1. For cis-trans isomerism, consider square planar and octahedral geometries primarily.
		2. Optical activity is lost if there is a plane of symmetry within the complex.

A.RAMA NAGESWARARAO · Answer

x = 2, tetrahedral

A.RAMA NAGESWARARAO · Answer

x = 4, square planar

A.RAMA NAGESWARARAO · Answer

The correct Option is "x = 4, octahedral"

A.RAMA NAGESWARARAO · Answer

x = 6, octahedral

NEET Chemistry Coordination Compounds MCQs

Select Topic

Question Tags

Question Tags

NEET Subjects

Our Bots

Company