Ligand substitution and percipitation reactions
Why is it that the (H2O)6 in a metal-aqua complex get replaced completely by 6NH3 but not by 2NH3 or 3NH3?
e.g [Cr(H2O)6]^3+ + 6NH3 ---> [Cr(NH3)6]^3+ + 6H20
but when reacted with 3NH3 it makes Cr(OH)3(H2O)3 + NH4^+ instead of Cr(H2O)3(NH)3 + 3H2O
e.g [Cr(H2O)6]^3+ + 6NH3 ---> [Cr(NH3)6]^3+ + 6H20
but when reacted with 3NH3 it makes Cr(OH)3(H2O)3 + NH4^+ instead of Cr(H2O)3(NH)3 + 3H2O
I guess you meant precipitation.
Since NH3 is alkaline, you're adding OH- ions. These pull one of the H off one of the six waters, producing H2O and leaving behind OH as the ligand. Do that three times and you've got yourself a neutral compound, which forms the ppt. If you add more NH3, eventually the NH3's start doing ligand substitution on the waters and OH-'s and once you start replacing the OH-'s it once again forms an ion, which dissolves.
Since NH3 is alkaline, you're adding OH- ions. These pull one of the H off one of the six waters, producing H2O and leaving behind OH as the ligand. Do that three times and you've got yourself a neutral compound, which forms the ppt. If you add more NH3, eventually the NH3's start doing ligand substitution on the waters and OH-'s and once you start replacing the OH-'s it once again forms an ion, which dissolves.
Original post by Pigster
I guess you meant precipitation.
Since NH3 is alkaline, you're adding OH- ions. These pull one of the H off one of the six waters, producing H2O and leaving behind OH as the ligand. Do that three times and you've got yourself a neutral compound, which forms the ppt. If you add more NH3, eventually the NH3's start doing ligand substitution on the waters and OH-'s and once you start replacing the OH-'s it once again forms an ion, which dissolves.
Since NH3 is alkaline, you're adding OH- ions. These pull one of the H off one of the six waters, producing H2O and leaving behind OH as the ligand. Do that three times and you've got yourself a neutral compound, which forms the ppt. If you add more NH3, eventually the NH3's start doing ligand substitution on the waters and OH-'s and once you start replacing the OH-'s it once again forms an ion, which dissolves.
Thank you
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