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Precipitation of Salts & Identification of Unknown Solutions

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´╗┐Precipitation of Salts & Identification of Unknown Solutions Date: 28/03/2012 Aim: To investigate different precipitates of salts in various combinations of cations and anions and identify the unknown solutions. Materials: 1. Test tubes 2. Test tube rack 3. Bottle brush 4. Distilled water bottle 5. Solubility table 6. Unknown olutions Anion solutions (sodium salts)- 1. Chloride 2. Carbonate 3. Sulfate 4. Hydroxide Cation solutions (nitrate salts)- 1. Copper 2. Barium 3. Lead 4. Silver 5. Magnesium 6. Iron (III) 1. Unknown solutions A-D Method: PART 1 1. Mix all possible combinations of the anions and cations in a clean test tube to produce precipitates of each of the four anions. 2. Record all observations, especially the formation of precipitates in a clear results table. The colour and appearance of the final products should be noted. 3. Write balanced equations for each of the chemical reactions that produce precipitates. The balanced equations will need to include states so that it is clear which product is the precipitate that formed. Full species equations are preferred. PART 2 1. Using the data from part 1 of the experiment, the solubility table, flow chart or information gathered from previous formative practicals; carry out a series of reactions to identify the unknown solutions A-D. The cation and the anion must be identified in each solution. 2. Record all results obtained from tests conducted on each unknown solution. From these, identify the names of the chemicals that you believe to be each of the unknowns, A-D. ...read more.


Hence, I expected a precipitation reaction to take place between the salts containing either Ag+ or Pb2+, individually. Though the reaction between sodium chloride and silver nitrate produced silver chloride and sodium nitrate, a precipitation reaction, the reaction between sodium chloride and lead nitrate contradicted the solubility rule in regards to chlorides. Rather than a precipitate being produced in the tube, a clear, slightly misty solution was formed as a result of the reaction between the anions and cations. A major contributing factor towards this error would have been a contaminated test tube. As expected, all the reactions containing carbonate ions produced a variety of precipitates, since most of them are insoluble. As opposed to the other anions in this experiment, carbonate was the only type of anion that corresponded to the solubility rules. This may have been due to cleaner test tubes being used in comparison to the ones used for the other anions. Like chlorides, the majority of salts composed of sulfate anions are soluble in aqueous solutions with the exception of Ba2+, Sr2+ and Pb2+. Cations such as Ca2+, Hg+ and Ag+ are slightly soluble. Though Ba2+ and Pb2+ produced precipitates -individually, Ag+ having a lesser insolubility rate failed to form a precipitate. Instead of a precipitation reaction occurring between sodium sulfate and silver nitrate, a clear, but slightly misty solution was produced. Hence, the final product refuted the solubility rule in regards to the anion sulfate. ...read more.


However, when I compared to the results of unknown solution to that of the results from activity one, there were anions that had extremely similar results. It was down to CO32- and OH- as both of them produced precipitates that were blue, orange/brown and cream. All hydroxides are insoluble in aqueous solution, however in this case; Fe3+ didn?t produce a precipitate with the hydroxide, hence differing with the solubility rules. Therefore, I think CO32- is the unknown solution as it corresponded better with the results from activity one and it also satisfied the solubility rules. One of the main problems in this task is the way I described the observations. Since it varied throughout the experiment, one slight change may have influenced the identification of the unknown solutions, as one result of a reaction is very similar to the other at times. Therefore, this might have caused a few errors. This can be eliminated by ensuring that correct terminology is used and the manner in which observations are described is consistent. As mentioned earlier, the contamination of test tubes was a major drawback in this experiment and this can be easily eliminated by ensuring that test tubes are thoroughly cleaned and dried before and after use. Conclusion: The various combinations of cations and anions enabled me to investigate the precipitation of salts. With this knowledge and the help of the solubility table I was able to write balanced equations and ionic equations. Using the results from activity one, I was able to identify the four unknown solutions. Unknown A-Barium nitrate, Unknown B- Silver nitrate, Unknown C-Sodium sulfate and Unknown D- Sodium carbonate. ...read more.

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