Question

Cobalt (III) chloride forms a green-colored complex ‘X’ with NH\(_3\). Number of moles of AgCl formed when excess AgNO\(_3\) solution is added to 100 mL of 1M solution of ‘X’ is:

• A. 0.3
• B. 0.2
• C. 0.1
• D. 1

Hint:

Each mole of \([Co(NH_3)_6]Cl_3\) releases 3 moles of Cl\(^-\) ions, which react with AgNO\(_3\) to form AgCl.

Answer 1

The Correct Option is C

Step 1: Identifying the Complex
- The green complex formed is \[Co(NH_3)_6\]Cl\(_3\).
- This means that for each molecule of the complex, 3 chloride ions are available for precipitation. Step 2: Moles of Complex and Cl\(^-\) Ions
- Given: 100 mL of 1M solution \( \Rightarrow \) Moles of complex = 0.1 moles.
- Each mole of the complex releases 3 moles of Cl\(^-\). \[ \text{Moles of Cl\(^{-}\) = } 0.1 \times 3 = 0.3 \text{ moles} \] Step 3: Reaction with AgNO\(_3\)
- AgNO\(_3\) reacts with Cl\(^-\) to form AgCl precipitate:
\[ Ag^+ + Cl^- \rightarrow AgCl \text{(s)} \] - Since each Ag\(^+\) reacts with one Cl\(^-\), the number of moles of AgCl precipitated is 0.3 moles.
Thus, the correct answer is 0.3 moles. \bigskip

Answer 2

Cobalt (III) chloride forms different coordination complexes with ammonia. The green-colored complex of cobalt (III) with ammonia is typically:

[Co(NH₃)₄Cl₂]Cl

This is a coordination complex where:
- Co³⁺ is the central metal ion
- 4 NH₃ molecules are coordinated to Co³⁺
- 2 Cl⁻ ions are also coordinated (within the coordination sphere)
- 1 Cl⁻ is present as a free ion outside the coordination sphere

When this complex is treated with excess AgNO₃, only the free chloride ion (outside the coordination sphere) reacts with Ag⁺ to form AgCl:
Ag⁺ + Cl⁻ → AgCl↓

Given:
Concentration of complex solution = 1 M
Volume = 100 mL = 0.1 L
Number of moles of complex = 1 mol/L × 0.1 L = 0.1 mol

Since each mole of the complex gives 1 mole of free Cl⁻,
Number of moles of AgCl formed = 0.1 mol

Therefore, the correct answer is:
0.1