Question

When a coordination compound $COC{l_3} \cdot 6N{H_3}$ is mixed with $AgN{O_3}$, ${\text{3 moles}}$ of ${\text{AgCl}}$ are precipitated per mole of the compound. Write
i) Structure formula of the complex.
ii) IUPAC name of the complex.

Answer 1

Hint: The reactant and one of the side products is given in the reaction itself. One can guess the product formed as complex by analyzing all the elements. While making the chemical structural formula for complex one should satisfy the oxidation state and the valency of the elements. The IUPAC naming should be done according to rules for the complex.

Complete step by step answer:
1) First of all let's analyze the data given in the question and form up a chemical reaction equation for the same which is as follows,
$CoC{l_3} \cdot 6N{H_3} + AgN{O_3} \to {\text{ Complex + }}3{\text{ moles of AgC}}{{\text{l}}_{(s)}}$
2) The silver chloride formed is a solid and gathers at the bottom as a precipitate. Now by using the above reaction information we can now write the chemical structural formula for the complex which is as follows,
$\left[ {Co{{\left( {N{H_3}} \right)}_6}} \right]C{l_3}$
3) The whole reaction can be written as follows,
$\left[ {Co{{(N{H_3})}_4}} \right]C{l_3} + 3AgN{O_3} \to \left[ {Co{{(N{H_3})}_6}} \right]C{l_3} + 3NO_3^ - + 3AgC{l_{(s)}}$
In the above reaction the coordination compound is reacted with the three moles of silver nitrate which produces the three moles of silver nitrate as the precipitate and the complex where there are six ammonia molecules are present in the coordination sphere and the three chlorine atoms are present in the ionization sphere.
4) Now let's write the IUPAC name for the complex $\left[ {Co{{\left( {N{H_3}} \right)}_6}} \right]C{l_3}$ as follows,
First, write the coordination sphere molecules which are six ammonia molecules which are written as Hexaamine. The second word should be written as the metal and its oxidation state which in this case is Cobalt(III) which has an oxidation state as three. Lastly, the ionization sphere element is written which is chloride ion. Therefore, the IUPAC name will be Hexaamminecobalt(III) chloride.
5) Therefore, the Structure formula of the complex is $\left[ {Co{{\left( {N{H_3}} \right)}_6}} \right]C{l_3}$.
IUPAC name of the complex is Hexaamminecobalt(III) chloride.

Note:
The oxidation state of metal cobalt is determined by the number of ions present in the ionization sphere which in this case there are three chloride ions present which gives the oxidation state of the cobalt metal. While writing the IUPAC name the oxidation state must be written in roman numbers right after the name of the central metal.