Question

On treatment of 100 ml of 0.1 M solution of CoCl₃·6H₂O with excess AgNO₃; 1.2 × 10²² ions are precipitated. The complex is ______.

Options

• [Co(H₂O)₆]Cl₃

• [Co(H₂O)₅Cl]Cl₂.H₂O

• [Co(H₂O)₄Cl₂]Cl.2H₂O

• [Co(H₂O)₃Cl₃].3H₂O

Answer 1

On treatment of 100 ml of 0.1 M solution of CoCl₃·6H₂O with excess AgNO₃; 1.2 × 10²² ions are precipitated. The complex is `bbunderline([Co(H_2O)_5Cl]Cl_2.H_2O)`.

Explanation:

Given: Volume = 100 mL = 0.1 L

Molarity = 0.1 M

Formula: Moles of complex = Molarity × Volume

= 0.1 × 0.1

= 0.01 mole

Number of moles of ions precipitated

= 1.2 × 10²² Cl⁻

= `(1.2 xx 10^(22))/(6.022 xx 10^(23))`

= `(1.2 xx 10^(22) xx 10^(-23))/(6.022)`

= `(1.2 xx 10^(-1))/(6.022)`

= `0.12/6.022`

= 0.019 ≈ 0.02 moles

∴ Number of Cl⁻ present in ionisation sphere = `"Number of moles of ions precipitated"/"Number of moles of complex"`

= `0.02/0.01`

= 2 Cl⁻ ions

So, each complex releases 2 free chloride ions on treatment with AgNO₃.