Question

ANAL 364 The Chemisery and Qualiative Analysis of Cations Group Separaions and Separations of Group 1 Catioms 27 Post-Laboratory Questions (Use the spaces provided for the answers and additional paper if necessary.) 1. What are the properties of the Group I, I1, and I cations that permit their separation by groups? (2) The precipitate was separated from the supernatant liquid in (1) and was found to be insoluble in hot water. The precipitate turned grey-black upon addition of 6M NH, The student concluded that the unknown contained Hg,2 ion. The student received a low mark on the experiment, because the unknown actually contained all three Group I cations. Explain what happened 2. (1) What is the electron configuration of Hg ion? 5. Many of the reactions utilized in this laboratory experiment involve substances with small solubility product constants. AgCl is one such substance. Nev- ertheless, a precipitate of AgCl will dissolve in either 6MHCI or 6M NH (1) Briefly explain why each of these reagents dissolves AgCl(s). Write appropriate equations to 2+ ion rather (2) Why does it actually exist as Hg2 than as Hg ion? (3) When Hg22 ion disproportionates, why does it become Hg(s) and Hg ion rather than form species with some other oxidation numbers? support your answer. 3. FeS(s) dissolves by the addition of HNO3 in a manner similar to that of CuS(s). In the process, the Fe ion is cxidized to Fe3 ion. Write an equation for this reaction. (2) Briefly explain why it is possible to reprecipitate AgCl(s) by adding HCI to [Ag(NH)2] lon but not by adding ammonia to [AgCl2r ion. Write appropriate equations to support your answer. 4. A student mistakenly added concentrated (12M) HCI to a sample of unknown, instead of adding 6M HCI, as directed. (1) At first, a large amount of light-colored pre- cipitate formed, but some dissolved on further addi- tion of concentrated HCI. Write an equation(s) for the reaction(s) that might have occurred. section date name

Answer 1

Cations are classified into group based on their stalubility product (Ksp) values. Higher the Ksp Values more will be the soluble compound • In case of group 1, Hght, Pb2+, Agt gets precipitated as their chlorides is the presence of dil-HCl. Because they have smaller Ksp Values which (AgCl, Hg2 Cl₂ , Ag (1) are easily exceeded by adding dil Hel (less ci concentration). Therefore we get lonie product valures higher then Ksp. Thus, chlorides gets easily forecipitated

A Chlorides of only gp. 1 gets precipitated and not of higher groups because they have higher Ksp values i to exceed their koplie, to have Ionic product greater than Ksp) Conci Hel is required which is not | Used in group 1. • Similarly In group I, cations like Hight, Cult, Bi3+ etc. are frecipitated as their sulfides in acidie medium so as to maintain low concentration of s2-ions so that higher group members do not get precipitate out. . Similarly, In group I, fest, Art, C3 get forecipitated as hydroxides in basic media . Conclusion: Cations are divided into groups based on Ksp and solubilety criteria.