For the reaction given below :
CoCl₃ . xNH₃ + AgNO₃ (aq) →
If two equivalents of AgCl precipitate out, then the value of x will be _____________.

Solution

Chemistry ma’am · 3 steps

Only chloride outside the bracket meets Ag⁺, so fill the six sites with what remains inside.

1. Ionisable chloride. AgNO₃ precipitates only the chloride ions in the outer sphere. Chloride bonded to cobalt stays in the complex. Two equivalents of AgCl mean 2 of the 3 chlorides are outside, so 1 chloride sits inside as a ligand.
2. Fill six sites. Cobalt is Co³⁺ here, and its coordination number is 6. One site holds Cl⁻, so NH₃ fills the other 6 - 1 = 5 sites.

   [Co(NH₃)₅Cl]Cl₂ + 2AgNO₃ → [Co(NH₃)₅Cl](NO₃)₂ + 2AgCl v

3. So. The complex is [Co(NH₃)₅Cl]Cl₂, which is CoCl₃.5NH₃, so x = 5.

The common slip: 6. Giving all six sites to NH₃ gives 6, but then all three chlorides are outside and three equivalents of AgCl would form.

The idea to keep. Moles of AgCl count the chlorides outside the bracket. The chlorides left inside, plus the NH₃, must add up to the coordination number, which is 6 for Co³⁺.

Answer from the NTA final answer key. Solution by PrepWiser.