Question

A compound formed by reacting CoCl\(_2\) with excess NH\(_3\) gives 1 mol of AgCl with AgNO\(_3\). Form the compound:

• A. [Co(NH\(_3\))\(_6\)]Cl\(_2\)
• B. [Co(NH\(_3\))\(_4\)Cl\(_2\)]Cl
• C. [Co(NH\(_3\))\(_5\)Cl\(_2\)]Cl
• D. [Co(NH\(_3\))\(_3\)Cl\(_3\)]

Hint:

When dealing with coordination compounds, always consider the number of ligands and the number of counterions. The formation of AgCl helps confirm the presence of free chloride ions outside the coordination sphere.

Answer 1

The Correct Option is A

When cobalt(II) chloride (CoCl\(_2\)) reacts with excess ammonia (NH\(_3\)), it forms a coordination complex. The formation of 1 mole of AgCl upon adding AgNO\(_3\) indicates that there is 1 chloride ion as a counterion outside the coordination sphere. The complex formed is [Co(NH\(_3\))\(_6\)]Cl\(_2\), which contains 6 ammonia molecules as ligands and 2 chloride ions as counterions. - (A) is the correct compound, as the excess NH\(_3\) displaces the chloride ions to form a complex with 6 ammonia ligands. The other options have incorrect stoichiometry or incorrect coordination numbers.