Most typical ion-exchange resins are based on cross linked polystyrene.1
The aim of this experiment was to separate a mixture of Fe3+ and Ni2+ using the anion exchange resin, Amberlite IRA-400. We then had to determine the Ni2+ and Fe3+ content of the two solutions from experiment 2a. Nickel was determined by complexometric titration with standard EDTA and iron was determined by titration with potassium dichromate in HCl medium.
Method
The method was followed as per the practical manual (page 21-30). As this is a practical, perfect results can’t always be obtained; therefore we had to work quantitatively to be able to achieve maximum yield and an accurate result.
Results and observations
Part 4A
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Fe3+/Ni2+ was a green mixture, after heating the mixture, with HCl, it turned orange/red.
- The resin had a yellow reddish color.
- We had to make sure the resin did not run dry, there had to be liquid in the column at all times.
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The resin column became darker the second time (Fe3+ formed) 0.1M HCl was added
- After separation flask B had a yellow color and contained the iron solution; and beakers A had a light green color, see through, and contained the nickel solution.
Part 4B
The results and observations obtained in this part of the experiment are summarised below in table 1 and table 2 and in calculations. Details of the observations and results recorded in the laboratory can be found on the attached sheet.
Table 1-Results for determination of Ni2+ by titration with EDTA
Calculation
Concentration of nickel in the original mixture:
Table 2-Result for determination of Fe3+ by titration with dichromate after reduction
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When adding (drop wise, titration) 19.79 cm3 of dichromate to the Fe3+ mixture and a blue violet colour is obtained then you know it is the iron ion formed and you have to stop the reaction.
Calculation
Concentration of Fe3+ in original solution:
Discussion
The experiment was performed according to the procedure outlined in the practical manual. No deviations were made. In part A of the experiment it was found that beaker A contained a green solution which was the nickel solution; and that flask B contained a yellow solution which was the iron solution. Care was taken to ensure that the product was quantitatively transferred at each step so that an accurate result could be established. In doing so the, yellow, iron concentration in the original solution was 0.0392M and the, green, nickel had a concentration of 0.00225M.
The absorption of a specific metal cation to the resin in the form of its anionic chloro complex depends on the specific nature of the complex as well as its concentration and the dissociation constant. In this experiment Ni2+ absorbs poorly to Amberlite IRA-400 at all chloride concentrations but Fe3+ absorbs strongly in concentrated HCl. When 0.1M HCl passes through the resin column the Fe3+ is poorly absorbed and the separation is affected.
Fe3+ and Ni2+ are in the transition metal group, which is known to be very resistant to most reactions, meaning their mixtures of ions can also be separated.
Conclusion
The experiment illustrated an interesting example of how to separate a mixture of Fe3+ and Ni2+ by using an anion exchange resin. In doing so a yellow solution, Fe3+, and a green solution, Ni2+, was yielded. These two solutions was then titrated, by means of different procedures that can be followed in the practical manual, to determine the content of the two solutions, the concentration of both ions in the original solution. It was found that iron had an original concentration of 0.0392M and nickel had a concentration of 0.00225M.
References
- Inorganic chemistry 244 practical manual, University of Stellenbosch, 2010, p. 8-12
- Greenwood, N. N.; & Earnshaw, A. (1997). Chemistry of the Elements (2nd Ed.), Oxford:Butterworth-Heinemann.
- Ion exchange (D. Muraviev, V. Gorshkov, A. Warshawsky), M. Dekker, New York, 2000.
