Lxperiment 26A Group I Cations Introduction Most metal halide ion, Ag\'; mercuro
ID: 1040695 • Letter: L
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Lxperiment 26A Group I Cations Introduction Most metal halide ion, Ag'; mercurous ion, Hg,; and lead(II) ion. solution of metal cations leads to the selective s are soluble in silver water and dilute hydrochloric acid. The exceptions are Consequently, the addition of HCI to a e precipitation of these three ions. While the theory the general discussion paration and identification of these ions has been outlined in me, some aspects of this chemistry need to be highlighted AgCI, Pciz, and Hg Cl, are all white solids. The Pb ions have the greate form soluble (PbC. solubility o while in concens f the ons in the presence of chloride. PbCl, is appreciably soluble in hot nures must be trated HCI, the salt reacts to carefully to guarantee that Pb2+ is trapped as the solid chloride salt. The following procedures Hg Cl, is unstable in the presence of base. isproportionate to form an atom of Hg and a mercuric ion. Hg lets of metallic mercury confirms the presence of mercury raise the pH, the Hg2.ions react to forn the white solid HgCl ofH C?NH2 and then a mixture of droplets of liquid mercury metal and a white s have a variable particles of solid. . The appearance of dark drop- Note that with the use of ammonia to solid HgCINH2. Thus, the product formed is atom of He an nder these conditions, the two Hg(l) ions of Hg Cl appearance from gray to dark gray depending on the size of the white solid of silver Finally, the presence of silver ions is determined based on whether a w chloride forms upon acidification of the solid remaining after thereita precipitation of mercury and HCI. The chlo- I. The HgC?NH2. Note that the acidification is accomplished with nitric acid rather than ride necessary for the precipitation of silver ions is already present from t Group I metal cations by the addition of HCI. the initial removal of the SAFETY Hydrochloric acid and nitric acid are strong acids and should be handled carefully. Spills should be NOTES: Safety goggles and gloves will be required for all steps of the laboratory romate compounds are carcinogenic when inhaled: care should be taken to avoid contact with the K CrO4 solution. cleaned up immediately. If contact is made with your skin, rinse thoroughly with water. Ch Unwanted chemicals are not to go down the sink. They are to be put in a designated container See your instructor for disposal instructions. Experimental Procedures As a reminder on the proper use of the centrifuge and how to decant properly, you may want to review General Laboratory Equipment and Procedures Step 1. Removal of Pb, Ag , and Hg2. Obtain I to 2 ml of the solution of unknown cations. If you must choose from multiple unknown solutio ns, record the number of your unknown. To the solution of unknown cations, add 10 drops 297 2014 Pcarson Edacation, Inc CopyrightExplanation / Answer
In step 1, Since in concentrated HCl, water soluble salt (PbCl4)2- formed so we must add 6M HCl dropwise in each and every moment to avoid the concentration increase of HCl. Also we should deal HCl carefully as it is a strong acid. While washing, distilled water must be sufficiently cold enough so that low amount of formded PbCl2 can be transferred to Pb2+ and stay in the residue as solid.
In step 2, Water must be hot enough so that the PbCl2 can be formed properly and comes in to the supernatant liquid.
In step 3, Since chromate compounds are carciogenic when inhaled, care should be taken to avoid cantact with K2CrO4 solution.
In step 4, the decant liquid must be acidified properly with addition of excess con HNO3 only, HCl must not be used for acidification.
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