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Question:

Which one of the following complexes will consume more equivalents of aqueous solution of Ag(NO3)?

Na3[CrCl6]

[Cr(H2O)5Cl]Cl2

Na2[CrCl5(H2O)]

[Cr(H2O)6]Cl3

Solution:

The complex [Cr(H2O)6]Cl3 will consume more equivalents of aqueous solution of silver nitrate as it dissociates to give the maximum number of chloride ions per molecule of [Cr(H2O)6]Cl3 dissociated. The reaction with silver nitrate is a precipitation reaction where silver chloride (AgCl) is formed. The number of chloride ions available for reaction determines the amount of silver nitrate consumed. Let's analyze each complex:

  • Na3[CrCl6]: This complex will dissociate to give 3 Na+ ions and 1 [CrCl6]3- ion. No free chloride ions are available for reaction with AgNO3.

  • [Cr(H2O)5Cl]Cl2: This complex dissociates into [Cr(H2O)5Cl]2+ and 2 Cl- ions. Two equivalents of AgNO3 will react with these two chloride ions.

  • Na2[CrCl5(H2O)]: This complex dissociates into 2 Na+ ions and 1 [CrCl5(H2O)]2- ion. No free chloride ions are available for reaction with AgNO3.

  • [Cr(H2O)6]Cl3: This complex dissociates into [Cr(H2O)6]3+ and 3 Cl- ions. Three equivalents of AgNO3 will react with these three chloride ions.

Therefore, [Cr(H2O)6]Cl3 will consume the most equivalents of AgNO3 because it releases the largest number of free chloride ions upon dissociation.