If the ammonia solution of Na were not completely converted to NaNH2, how would this affect the subsequent preparation of [Cr(NH3)6](NO3)3?
If a large excess of Fe(NO3)39H2O were added to the NH3 solution of Na, how would this affect the yield of [Cr(NH3)6](NO3)3 and why?
Preparation of [Cr(NH3)6](NO3)3 involves two main reactions:
CrCl3 + 6 NH3 [Cr(NH3)6]Cl3 .....(1)
[Cr(NH3)6]Cl3 + 3 HNO3 [Cr(NH3)6](NO3)3 + 3 HCl .....(2)
In the first step NaNH2 is added for the formation of [Cr(NH3)6]Cl3. Without NaNH2 formation of [Cr(NH3)5 Cl]Cl3 takes place. NaNH2 releases NH2- in the reaction medium. Since NH2- is a better nucleophile than NH3, it facilitates the removal of Cl directly bound to Cr from its chromium complex thus forming [Cr(NH3)5(NH2)]2+ which adds a proton to form [Cr(NH3)6]Cl3. So if the Na solution of liquid ammonia is not completely converted to NaNH2 we will have less NH2- in the solution and thus some amount of [Cr(NH3)5Cl]Cl3 will also be formed. This will decrease the yield of our product.
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