Question

What is the number of moles of silver chloride precipitated when excess silver nitrate is treated with one mole of pentaamminecarbonatocobalt (III) chloride?

• A. 4
• B. 3
• C. 2
• D. 1

Hint:

In reactions involving coordination compounds, pay attention to the number of chloride ions in the complex and how they participate in reactions with other compounds.

Answer 1

The Correct Option is B

Step 1: Understanding the Question:
We need to determine the amount of silver chloride (\( \text{AgCl} \)) precipitate formed. This depends on the number of chloride ions present outside the coordination sphere of the complex.
Step 2: Key Formula or Approach:
Write the coordination formula of the complex and identify the ionizable chloride ions. Only chloride ions outside the brackets \( [ ... ] \) react with silver nitrate.
Step 3: Detailed Explanation:
The name of the complex is pentaamminecarbonatocobalt (III) chloride.
Coordination formula: \( [\text{Co}(\text{NH}_3)_5(\text{CO}_3)]\text{Cl} \).
In this complex:
- The coordination sphere contains one cobalt atom, five ammonia ligands, and one carbonate ligand.
- There is only one chloride ion (\( \text{Cl}^- \)) outside the coordination sphere as a counter-ion.
When treated with excess silver nitrate (\( \text{AgNO}_3 \)):
\[ [\text{Co}(\text{NH}_3)_5(\text{CO}_3)]\text{Cl} + \text{AgNO}_{3(\text{excess})} \longrightarrow [\text{Co}(\text{NH}_3)_5(\text{CO}_3)]\text{NO}_3 + \text{AgCl} \downarrow \]
Since there is 1 mole of ionizable chloride per mole of complex, 1 mole of \( \text{AgCl} \) will precipitate.
Step 4: Final Answer:
The number of moles of silver chloride precipitated is 1.