Animated Solution for Chemistry - Coordination Compounds: One mole of the complex compound $Co(N{H}_3{)}_{5}C{l}_3$, gives 3 moles of ions on dissolution in water. One mole of the same complex reacts with two moles of $AgN{O}_3$ solution to yield two moles of $AgCl(s)$. The structure of the complex is

The label simply reads: $Co(N{H}_3{)}_{5}C{l}_3$. This is its empirical formula—it tells us what atoms are inside, but it keeps the secret of how they are arranged.

To crack this case, we need to rely on the brilliant framework laid down by Alfred Werner, the father of coordination chemistry. Werner proposed that metals in these complexes possess two types of valencies: 1. Primary Valency: These are the ionizable counter-ions that sit outside the coordination sphere (the square brackets). They dictate the charge of the complex. 2. Secondary Valency: These are the non-ionizable ligands trapped inside the coordination sphere, directly bonded to the central metal atom.

The problem states that one mole of our mysterious complex reacts with excess $AgN{O}_3$ to produce exactly two moles of Silver Chloride ($AgCl$) precipitate.

Why is this crucial? Because $AgN{O}_3$ is like a bouncer—it only interacts with the free, ionizable chloride ions ($C{l}^{-}$) roaming outside the coordination sphere. The chloride ions locked inside the bracket are protected and won't react.

Since we get two moles of $AgCl$, we can definitively conclude that there are two ionizable $C{l}^{-}$ ions outside the square bracket.

Counting the Ions Now, let's piece the puzzle together. Our original formula has a total of three chlorine atoms. If two of them are outside the bracket, the remaining one chlorine atom must be inside. Furthermore, all five ammonia ($N{H}_3$) molecules must also be inside, acting as ligands to satisfy the secondary valency of the cobalt ion.

This gives us the structural formula: $[Co(N{H}_3{)}_{5}Cl]C{l}_2$.

But wait, we have one more piece of evidence to verify! The problem mentions that dissolving one mole of the complex in water yields three moles of ions. Let's test our proposed structure:

When this complex dissociates, it produces one complex cation ($[Co(N{H}_3{)}_{5}Cl{]}^{2+}$) and two chloride anions ($2C{l}^{-}$). $1+2=3$ ions!

The evidence aligns perfectly. The mystery is solved, and the true identity of our complex is $[Co(N{H}_3{)}_{5}Cl]C{l}_2$.