What's the formula for cobalt II nitride pentahydrate?

Just looking at the name, I'd have to say

Co3N2 • 5H2O

To determine the formula for cobalt II nitride pentahydrate, we need to understand the charges of the ions involved and how they combine.

First, let's break down the name of the compound:

- "Cobalt II" means that cobalt is in its +2 oxidation state.
- "Nitride" refers to the nitride ion, which is N³⁻.

To determine the formula, we need to balance the charges of the ions. Since cobalt is in its +2 oxidation state and the nitride ion is N³⁻, we need two nitride ions to balance the charge of one cobalt ion. Therefore, we have Co²⁺(N³⁻)₂.

Next, we see that the compound is a pentahydrate, which means it contains five water molecules. The formula for a water molecule is H₂O, where hydrogen has an oxidation state of +1 and oxygen has an oxidation state of -2. Therefore, we have 5(H₂O).

Putting it all together, the formula for cobalt II nitride pentahydrate is Co(N)₂•5H₂O.