Question

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??

Answer 1

`"0.0024 mols"` of `"AgCl"`.

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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.

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.