Naming this compound

[CenCen]

How would you name the following compound:

[Co(NH₃)₅Cl]Cl₂

Can you explain the process of finding the oxidation number?

I named it: Pentaamminechloro cobalt (III) dichloride

[Erin Min]

[Co(NH3)5Cl]Cl2

Pentaammine Chloro Cobalt (III) chloride

You are correct.


To calculate the Oxidation number of Cobalt (Co), you must find the charge of the Dichloride Anion. The dichloride anion comes out to a charge of -2. The coordination complex must have a net charge of +2, therefore the Co must have a charge of +3 to count for the -1 charge of the Cl anion (Ammine anion is neutral). Co's oxidation number is 3 (III).

[Vanessa A 3F]

The correct answer is pentaamminechlorocobalt (III) chloride
*Note that there is no di prefix in front of the chloride.

To find the oxidation number:
There are some atoms and polyatomic ions in coordination compounds that have a charge. These should be memorized, so that you know what proper oxidation to assign the metal.
In your example, NH₃ is neutral. Cl, however, has a charge of -1. There are three Cl atoms. That makes the charge (-1)(3)= -3. So to balance this, we assign cobalt the oxidation number of 3, or III.