Group I Cations-Group III Cations PDF

Preview

Summary

A. Guide Questions for Group I Cations What metals are members of Group II Cations? Members of Group II Cations are berylium (Be), magnesium (Mg), calcium (Ca), strontium (Sr), barium (Ba), and radium(Ra). How can they be separated from other group cations? Groups II and other cations are separated ...

Description

A. Guide Questions for Group I Cations 1. What metals are members of Group II Cations? Members of Group II Cations are berylium (Be), magnesium (Mg), calcium (Ca), strontium (Sr), barium (Ba), and radium(Ra). How can they be separated from other group cations? Groups II and other cations are separated by precipitation of their insoluble sulfides. The sulfide ion is produced by the weak electrolyte gaseous hydrogen sulfide, which is only very slightly soluble in water. 2. How is lead ion separated and identified? When a metal ion or a group of ions forms insoluble salts with a specific anion, precipitation can separate them from the others. The anions can also be separated by precipitating them with the adequate metal ions. In identifying the lead the diluted HCl is added to an aqueous Pb2+ ion solution. When dilute HCl s is added to an aqueous Pb2+ solution, a white precipitate is formed. Lead(II) chloride is the white precipitate (PbCl2). 3. What is the purpose of adding ammonia to the precipitate? The addition of ammonia to the precipitates produces a complex ion known as the diamminesilver(I) ion, [Ag(NH3)2]+, which combines with silver ions to form a complex ion known as the diamminesilver(I) ion, [Ag(NH3)2]+. When a solution comes into contact with one of the silver halide precipitates, it contains very little dissolved silver ions. The addition of ammonia reduces this concentration even further. If the solubility product is less than the adjusted silver ion concentration multiplied by the halide ion concentration, some precipitate dissolves to restore equilibrium. This happens with silver chloride and, if the ammonia is concentrated, with silver bromide. The higher the concentration of ammonia, the further the equilibrium is pushed to the right, lowering the silver ion concentration. Because silver iodide is so insoluble, ammonia cannot lower the silver ion concentration sufficiently to dissolve the precipitate.

B. Guide Questions for Group II Cations 1. What metals are members of Group II Cations? The metals that are the members of the group II cations are 2. For each of the following pairs, identify a reagent that will dissolve one substance but not the other: HgS and As2S3 (NH4)2S HgS and Bi2S3 HNO3 As2S3 and Sb2S3 Concentrated HCl PbSO4 and CuSO4 Diluted HCl 3. Explain the theoretical aspect of the separation of Group IIA from Group IIB. Group II A Cations consist of Cd2+, Bi3+, Cu2+ and Hg2+. On the other hand, Group II B consist of As3+, As5+, Sb3+, Sb5+, Sn2+ and Sn4+. The cations are differentiated based on the difference in their electronegativities: Group II A cations have lower electronegativity and are thus, insoluble in (NH4)2S while Group II B cations have higher electronegativity and are therefore soluble in (NH4)2S.

C. Guide Questions for Group III Cations: 1. Account for the separation of aluminum ion from manganese ion, ferric ion, and cobalt ion. Write the complete reaction involved. Group III cations are precipitated as sulfides or hydroxides in an NH3-NH4Cl buffered solution containing ammonium sulfide (NH4OH + H2S). The cations are divided into two subgroups by the action of strong base (KOH) upon a solution of the cations. Group IIIA (Cr+2 , Zn+2, Al+3 ) hydroxides dissolve in x’s KOH forming the soluble group. Group IIIB (Mn+2 , Fe+3, Ni+2, Co+2) hydroxides precipitate to form the insoluble group. Addition of H2O2 oxidizes Cr+3 → Cr+6O4-2, Fe+2 → Fe+3, Mn+2 → Mn+4, and Co+2 → Co+3. Hydroxides in higher valence states are more insoluble than in the lower states. Peroxides treatment causes easier separation of the subgroups of group III.

2. What is the property of Al(OH)3 which, when reacting with organic dyes, serves as confirmatory test? Al(OH)3 has the property of absorbing organic dye, or alizarin dye, which serves as the confirmatory test for Aluminum ion.

3. How is manganous ion identified? What is the reaction involved? Manganous ion, in acidic medium is oxidized to purple permanganate ion, MnO 4 - by sodium bismuthate. Formation of the purple MnO4- serves as a sensitive test for the detection of Mn +2 .

4. Enumerate the ions that form colored complexes during the confirmatory test. Identify their characteristic colors. Chemical Formula of the Complex Ion 1. Aluminum ion (Al3+) Al3+(aq) + 3NH3(aq) + 3H2O(l) Al(OH)3 + 3NH4+(aq) 2. Manganese ion (Mn2+) 2Mn2+(aq) + 5NaBiO3 2MnO4- + 5Bi3+ (aq) + 5Na+(aq) + 7H2O

Characteristic Color reddish purple supernatant

purple complex

3. Ferric ion (Fe3+) Fe3+ + SCN- FeSCN2+

dark-reddish brown complex

4. Cobalt ion (Co2+) Co2+ + 4SCN- [Co(SCN)4]2-

intense blue-colored complex

D. After studying the separation scheme for Group I to III cations

(a) devise a flow chart or schematic diagram to separate and confirm the presence of the given ions in the solution below;

a.)...