Discussion Forum



1)

On the treatment of 100 mL of 0.1 M solution of CoCl3. 6H2O with an excess of AgNO3: 1.2× 1022 ions are precipitated. The complex is


A) $[Co(H_{2}O)_{4}Cl_{2}]Cl.2H_{2}O$

B) $[Co(H_{2}O)_{3}Cl_{3}].3H_{2}O$

C) $[Co(H_{2}O)_{6}]Cl_{3}$

D) $[Co(H_{2}O)_{5}Cl_{}]Cl_{2}.H_{2}O$

Answer:

Option D

Explanation:

Molarity (M)

            = Number of moles of solute/Volume of solution (in L)

$\therefore$    number of moles of complex=  $\frac{Molarity \times volume ( mL)}{1000}$

               = $\frac{0.1 \times 100}{1000}=0.01 mole$

   Number of  moles of ions precipitate= $\frac{1.2 \times 10^{22}}{6.02 \times10^{23}}=0.02 mole$

$\therefore$   Number of Cl- present in ionisation sphere

       = Number of moles of ions precipitated/ Number of moles of complex

                              = $\frac{0.02}{0.01}=2$

$\therefore$ Cl- are present outside the square brackets. i.e. in ionisation sphere .Thus the formula of complex is 

[Co(H2O)5Cl] Cl2 .H2O