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Complex Ion Composition By Jobs Method By Kelly Miller Smith, III Inorganic Chemistry Dr. Virgil Payne 1: 00 lab Objective The objective of this experiment is to study the continuous variations method that is used to determine the composition of the solution Ni 2 + ethylene diamine complexes. Background To examine the interaction between two molecules in solution without isolating the compound Jobs method is used. Although unstable compounds tend to be generated, this is not a reflection of weak interactions.
In some cases, the transition metal species cannot be crystallized from the solution and separated from the other species present. Without Jobs Method this composition can be very difficult to deduce. Jobs Method analyzes the value of n in the equilibrium: Z + nL &# 8594; Zln Varying the n value carries out the experiment. Absorbencies of each of the Zln complexes are obtained.
The sum of the concentrations of the metal, Z, and the ligand, L, are kept equal. With the ratio of the ligand to the metal in the solution with the maximum absorbance for the Zln complex, the value of n can be determined as well as the composition of Zln. The metal Ni 2 + and the ligand ethylene diamine (en) are studied in this experiment. Solutions are prepared with varying compositions of Ni (en) n 2 +. Using the equilibrium constants, it is possible to identify which species is present. If the constant for the formation of a species where n is 2 is larger than a species whose constant equals 3 then the former species is pre-dominant.
Jobs Method is limited in that it will give non-integral values of the n present if a fourth complex, Zln+ 1, exists. If there is a large variation between the equilibrium constants then only two complexes will be present in the prepared solutions. The absorbance values are plotted, then the value of n can be calculated. Procedure The procedure for this experiment can be found in Inorganic Chemistry Lab Manual prepared by Dr.
Virgil Payne. Data and Observations 530 545 578 622 640079 0. 134 0. 277 0. 555 0. 605088 0. 141 0. 333 0. 596 0. 638099 0. 154 0. 35 0. 57 0. 579158 0. 218 0. 414 0. 584 0. 552212 0. 289 0. 436 0. 459 0. 411376 0. 424 0. 396 0. 203 0. 149213 0. 224 0. 168 0. 061 0. 036 1 0. 052 0. 067 0. 142 0. 465 0. 647 Results and Discussion 1. Ni (en) 32 + Ni (en) 2 (H 2 O) 22 + Ni (en) 1 (H 2 O) 42 + 2. The higher placement in the electrochemical series of en is evidence that it has a higher energy of transition than H 2 O in the same complex. This gives en a higher ligand field strength. 5. Jobs Method would be useful in the reaction of Ni 2 + and NH 3 in H 2 O.
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