Determining the composition of a coordination compound using molar conductivity

In summary, the substance CoBr3 dot 4 NH3 dot 2 H2O has a molar conductivity of 42 kS/m at infinite dilution. By considering the ions present in the solution, we can estimate the composition of the coordination sphere. While there is no direct link between molar conductivity and coordination spheres, understanding the types, numbers, and charges of ions present can help determine the structure of the complex.
  • #1
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Homework Statement



The substance CoBr3 dot 4 NH3 dot 2 H2O ha a molar conductivity of 42 kS/m at infinite dilution. Indicate the composition of the coordination sphere.

Homework Equations



I don't know any relevant equations.

The Attempt at a Solution



Where can we read about how molar conductivity can tell us the composition of a coordination sphere? I googled this and have not found a tutorial on how to do this type of question.

I don't recall molar conductivity being mentioned in my high school chemistry class when we did coordination spheres.
 
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  • #2
There is no direct link, however, think how the molar conductivity depends on the ions present in the solution - types, numbers, charges... Once you can estimate what ions are present, you can conclude how the complex looks.

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  • #3


I can provide some guidance on how molar conductivity can be used to determine the composition of a coordination compound.

Molar conductivity is a measure of the ability of a substance to conduct electricity. In coordination compounds, the conductivity is affected by the presence of ions in solution, which can come from the central metal atom or the ligands attached to it.

In this case, the compound in question is CoBr3 dot 4 NH3 dot 2 H2O. This notation indicates that there are 4 ammonia (NH3) molecules and 2 water (H2O) molecules attached to each CoBr3 unit.

To determine the composition of the coordination sphere, we need to first understand the role of each component in the compound. The central metal atom, Co, is surrounded by three bromine atoms, which are negatively charged. The ammonia and water molecules, on the other hand, are neutral ligands that are attached to the metal atom through coordination bonds.

When the compound is dissolved in water, it dissociates into ions, including Co3+, Br-, NH4+, and OH-. These ions contribute to the overall conductivity of the solution.

At infinite dilution, the conductivity of the solution is solely due to the dissociation of the compound into its constituent ions. Therefore, by measuring the molar conductivity at infinite dilution, we can determine the total number of ions present in the solution.

In this case, the molar conductivity is given as 42 kS/m. This value can be compared to the theoretical molar conductivity, which can be calculated based on the number of ions present in the solution.

For CoBr3 dot 4 NH3 dot 2 H2O, the theoretical molar conductivity can be calculated as follows:

CoBr3 dot 4 NH3 dot 2 H2O -> Co3+ + 3 Br- + 4 NH4+ + 2 OH-

The theoretical molar conductivity is then given by:

Lambda = lambda_co3+ + 3 lambda_br- + 4 lambda_nh4+ + 2 lambda_oh-

Where lambda is the molar conductivity of each ion.

By using the experimental value of 42 kS/m and the known molar conductivities of each ion, the number of ions present in the solution can be calculated. This can then be used to determine the composition of the coordination sphere.

In
 

1. How is molar conductivity used to determine the composition of a coordination compound?

Molar conductivity is a measure of the ability of a substance to conduct electricity and is affected by the concentration and charge of ions present in a solution. By measuring the molar conductivity of a coordination compound at different concentrations, we can determine the number of ions present and their charges, which helps to determine the composition of the compound.

2. What is the relationship between molar conductivity and concentration for coordination compounds?

The molar conductivity of a coordination compound is directly proportional to its concentration. This means that as the concentration increases, the molar conductivity also increases. This relationship is used to determine the concentration of the compound and its composition.

3. Can molar conductivity be used to determine the charge of ions in a coordination compound?

Yes, molar conductivity can be used to determine the charge of ions present in a coordination compound. This is because the conductivity is affected by the charge of the ions, so by measuring the molar conductivity at different concentrations, we can determine the charges of the ions present.

4. How does temperature affect the molar conductivity of coordination compounds?

The molar conductivity of coordination compounds is affected by temperature. As the temperature increases, the conductivity also increases due to increased ion mobility. This must be taken into account when determining the composition of a coordination compound using molar conductivity.

5. Can molar conductivity be used to determine the molecular formula of a coordination compound?

No, molar conductivity alone cannot be used to determine the molecular formula of a coordination compound. It can only provide information about the number and charge of ions present. Other analytical techniques, such as spectroscopy, are needed to determine the molecular formula.

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