Chemistry Lab Manual

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Experiment 1. 2. 3. 4. 5. 6. Separation of chloride and bromide ions by ion exchange chromatography Spectrophotometric Analysis of a Two-Components System Valencies of Vanadium Synthesis and Studies of the Absorption Spectrum of Copper(II) Complexes Preparation and Analysis of Potassium cis-diaquadioxalatochromate(III) dihydrate Synthesis and Nitration of Tris(acetylacetonato)cobalt(III)

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EXPERIMENT 1 Separation of chloride and bromide by ion exchange chromatography Introduction The anion exchange resin used in this experiment (Deacidite FF’ or Amberlite) is a cross link polymer containing quaternary ammonium groups as integral parts of the polymer lattice and an equivalent amount of the chloride anions. The anion exchange resin, originally in the chloride form, is converted into the nitrate form by washing with sodium nitrate solution. The function of the ion exchange resin depends on the following chemical equilibrium: Resin-Cl + NO3Resin-NO3 + Cl-

The above equation shows that concentrated nitrate ion will shift the equilibrium to the right and chloride ion will be eluted from the column slowly. During the process, there is a difference in concentration of nitrate and chloride ions, hence equilibrium exist along the length of the column. The process of elution should be allowed to run slowly to attain equilibrium stability. Ion exchange procedure is used widely in synthesis and analysis. One important usage is in the separation of the actinide and lanthanide elements. In this experiment, a mixture of chloride and bromide ions will be separated quantitatively. These two anions exchange readily with the resin-nitrate, i.e. equilibrium shifts to the left in equation 1 when the solution mixture is poured into the column. The anions are eluted from the column when a solution of sodium nitrate is passed through the column. Separation is possible as bromide ion is adsorbed stronger than the chloride ion (Keq for Br- < Keq for Cl-). The progress of separation is followed by titrating 10 cm3 fraction of the eluate with standard silver nitrate solution. This titration uses chromate ion (CrO42-) as the indicator. Low concentration of the indicator is needed to achieve its end point when excess Ag+ is added. Blank titration is done to determine the actual volume of silver nitrate needed to form Ag2CrO4 and to determine the end point. Procedure. Preparation of column. Wash about 20 g of resin with distilled water in a beaker for several minutes. Any fine particles are removed by decantation, and the washing procedure is repeated several times until the color of the decanted washing is clear. Transfer the resin slurry


portionwise into a column that has a glass-wool plug at the lower end and is filled with water. (The tube may be tapped gently to prevent the formation of air bubbles). Wash the resin with dilute HNO3 until the washings are free from chloride ion (silver nitrate test). Fill a 250 cm3 separating funnel with 0.3 M NaNO3 and elute the HNO3 for 15 minutes. (To obtain a satisfactory separation, it is essential that the solutions should pass through the column in an uniform manner. The resin particles should be packed uniformly in the column: the resin bed should be free from air bubbles so that there is no channeling) Weigh out accurately about 0.10 g of A.R. sodium chloride and about 0.20 g of A.R. potassium bromide, dissolve in about 2.0 cm3 of water and transfer quantitatively to the top of the column with the aid of 0.3 M sodium nitrate. Pass 0.3 M sodium nitrate through the column at a flow rate of about 1 cm3 per minute and collect the effluent in 10 cm3 fractions. Transfer each fraction in turn to a conical flask and add 0.4 cm3 of 0.2 M potassium chromate solution as indicator and titrate with standard 0.05 M silver nitrate. Before commencing the elution, titrate 10.0 cm3 of the 0.3 M sodium nitrate (use the same amount of potassium chromate as indicator) with...
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