If excess of #AgNO_"3"# solution is added to 100 ml of 0.024 M solution of dichlorobis (ethylene diamine) cobalt (III) chloride, how many moles of #AgCl# will be precipitated??

1 Answer
Aug 10, 2017

#"0.0024 mols"# of #"AgCl"#.


Well, this is just a regular limiting reactants problem, with more complicated compounds. The only hurdle is figuring out what the dichlorobis(ethylenediamine)cobalt(III) charge is.

Dichlorobis(ethylenediamine)cobalt(III) chloride has:

  • two chloro ligands (#"Cl"^(-)#) in the inner coordination sphere.
  • two ethylenediamine ligands (#"H"_2"N"-"CH"_2-"CH"_2-"NH"_2#) in the inner coordination sphere.
  • a chloride (#"Cl"^(-)#) ligand coordinated on the outer coordination sphere.
  • cobalt(III), which has an oxidation state of... what is #"III"# in english?

The oxidation states add up as:

#overbrace(2 xx (-1))^"dichloro" + overbrace(2 xx 0)^("bis"("en")) + overbrace((+3))^"cobalt(III)" = (+1)#

Thus, it is written as...

#overbrace(["CoCl"_2("en")_2])^(+1)"Cl"#

The cis form is shown below.

https://upload.wikimedia.org/

The ethylenediamine ligands are bidentate, #sigma# donor, strong-field ligands, so it is likely that this complex is a low-spin complex, making it relatively inert in the inner coordination sphere.

So, the reaction is probably going to be an outer-sphere, double-replacement reaction:

#"AgNO"_3(aq) + ["CoCl"_2("en")_2]"Cl"(aq) -> "AgCl"(s) + ["CoCl"_2("en")_2]"NO"_3(aq)#

The complex is clearly the limiting reactant, so...

#"0.024 mol/L" xx "0.100 L" = "0.0024 mols complex"#

The complex is #1:1# with #"AgCl"#, so #ulbb"0.0024 mols"# of #"AgCl"# will be generated.