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The Separation and Identification of a Series of Cations By: Jason Hsieh Partners: Anna Wetherholt, Jung Soo Kim BB5 11/12/09 1 Abstract: This labs purpose involved identifying 10 cations with 11 other reagents and finding trends and properties that would enable one identify unknown cations for future labs. The techniques used involved using reagents such as acids, bases, acidic/basic H 2 S, chromates, and carbonates/phosphates, whereupon careful observations are recorded. Some noticeable trends involved how the first five ions, (lead, barium, bismuth, iron and manganese) generally formed precipitates with most reagents, whereas the other five (silver, copper, nickel zinc and aluminum) tended to form less. Also, the acids seemed to be the least reactive of the reagents and other trends were carefully noted. Introduction : This lab involved a series of reactions and tests to 10 cations in an attempt to chemically fingerprint them. The reactions included testing for amphoteric behavior (1), behavior in aqueous ammonia (2), behavior with sulfide ions (3), behavior in carbonate and phosphate solutions (4), and confirmatory tests (5). These tests are summarized as follows: 2 (1) Sn(OH) 2(s) + 2H + (aq) Sn 2+ (aq) + H2O (l) or Sn(OH) 2(s) + OH-(aq) Sn(OH)3- (aq) (2) Cu 2+ (aq) + 2OH- (aq) Cu(OH) 2(s) and (with excess ammonia) Cu(OH) 2(s) + 2NH 4 + (aq) + 2NH 3(aq) Cu(NH 3 ) 4 2+ (aq) + 2H 2 O (l) (3) M 2+ (aq) + S 2- (aq) MS (s) and has acidic/basic properties that enable the user to control the sulfide ion concentration by shifting the equilibrium by adding adjusting the pH S 2- + H+ HS- HS- + H + H 2 S (4) CO 3 2- (aq) + H 2 O (l) HCO 3- (aq) + OH- (aq) PO 4 3- (aq) + H 2 O (l) HPO 4 2- (aq) + OH- (aq) the hydroxide ion, carbonate ion, hydrogen carbonate/phosphate ion could combine with a metal to form a precipitate. The precipitate that forms can be identified in the Merck Index or similar reference book. (5) These are tests that confirm a certain product and observation. For example, adding KSCN (s) to Fe 3+ (aq) will form Fe(SCN) 2+ , a blood red solution Using all of these techniques and observing the reactions that take place enabled one to identify certain compounds easier. This is especially useful when identifying an unknown solution, and by chemically fingerprinting the cations in this lab, it will become easier to develop a plan in screening for a certain cation in the future. 3 Of course, such identification does not only occur in the academic field. As mentioned in lecture, identification of ions is important for knowing the kinds of contaminants in our water, and atmosphere. From third world countries to bottling water, the identity of what we drink is of vital importance. In Determination of Perchlorate at Trace Levels in Drinking Water by Ion-Pair Extraction with Electrospray Ionization Mass Spectrometry 1 , the EPA works to find out how much perchlorate is now in our drinking water. However, ion identification is not only limited to the environment. In the drinking water.... View Full Document

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