An excess of AgNO₃ is added to 100 mL of a 0.01M solution of dichlorotetraaquachromium(III) chloride. The numb

Question

An excess of AgNO₃ is added to 100 mL of a 0.01M solution of dichlorotetraaquachromium(III) chloride. The number of moles of AgCl precipitated would be:

Accepted Answer

1. **Determine the formula:** The IUPAC name 'dichlorotetraaquachromium(III) chloride' indicates the complex ion consists of Chromium(III), four aqua ($H_2O$) ligands, and two chlorido ($Cl^-$) ligands inside the coordination sphere. 
   *   Charge on complex ion = Oxidation state of Cr + Charge of ligands = $(+3) + 4(0) + 2(-1) = +1$.
   *   To balance this +1 charge, there must be one chloride ion ($Cl^-$) outside the coordination sphere. 
   *   Formula: $[Cr(H_2O)_4Cl_2]Cl$ .

2. **Identify Ionisable Chloride:** According to Werner's theory, only the anions present outside the coordination sphere (primary valency) are ionisable and can precipitate with $AgNO_3$. Here, there is **1 ionisable $Cl^-$** per formula unit .

3. **Calculate Moles:**
   *   Moles of complex = Molarity $	imes$ Volume (in Litres) = $0.01 	ext{ mol L}^{-1} 	imes 0.1 	ext{ L} = 0.001 	ext{ mol}$.
   *   Since 1 mole of complex yields 1 mole of $AgCl$ precipitate:
   *   Moles of $AgCl$ = $1 	imes 0.001 = 0.001 	ext{ mol}$.

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