Cations used are Ag,Al,Cu,Fe,Mn,Pb,Ba,Ni Chemistry 2068 General Chemistry Lab Ma

Question

Cations used are Ag,Al,Cu,Fe,Mn,Pb,Ba,Ni Chemistry 2068 General Chemistry Lab Manual Tables 1 and 2 provide Kp and Kr values for many of the substances available for your use. You should refer to these tables frequently t help you evaluate your data and plan your separation schemes. Table 1 Ksp values for metal salts. Salt Salt Salt Fe(OH)3 2.6 x 10 39 Fe2ss Cu(OH)2 1.6 x 10.19 Ag2so, 1.5 x 10 s Nis Al(OH)3 1.9 x 10 33 PbSO4 1.8 x 10 cuss 2.3 x 10 13 Ni(OH)2 1.4 x 10-8 Table 2: Kf values for complex ions Complex Ion Complex Ion 2.1 x 1034 AI(OH)4 Procedures L Cation. Reactivity with Specific Reagents A) Reactions the NaCl. Add the reagent drop wise (about 5 drops) to each cation solution. Avoid an excess of chloride ion at this point as some of the cations tend to form complex ions with chloride. IWhich ones?) Try the same reactions using 6 M HCL (CAUTIOND. Are the results any different? W equations for any reactions that occur. Check the Kp values and perform some simple calculations justify the formation of these precipitates.

Explanation / Answer

Started with Ag, Al, Cu, Fe, Mn, Pb, Ba, Ni

1. From A) and B)

1. Ag and Pb formed precipitate with HCl

Ag+ + Cl- --> AgCl(s)

Pb2+ + 2Cl- --> PbCl2(s)

PbCl2 dissolves in hot waterr, AgCl remined insoluble

When 15 M NH3 added, AgCl dissolves,

AgCl + 2NH3 --> [Ag(NH3)2]+(aq) + Cl-

With HNO3, reformation of AgCl precipitates occurs.

2. With SO4^2-, Ba,Ag and Pb reacted

Ba2+ + SO4^2- --> BaSO4(s)

2Ag+ + SO4^2- --> Ag2SO4(s)

Pb2+ + SO4^2- --> PbSO4(s)

with NaOH, all three dissolves to form Ba(OH)2, Pb(OH)2, Ag(OH)

with H2SO4, the precipitate reforms to give sulfates.

3. The metals can be separated by first adding 6 M HCl, separate the precipitate and then add SO4^2- to the solution.

From C) and D)

1. With NaOH, all metals reacted

Ag+ + OH- --> Ag(OH)(aq)

Al3+ + 3OH- --> Al(OH)3(s)

Cu2+ + 2OH- --> Cu(OH)2(aq)

Fe3+ + 3OH- --> Fe(OH)3(s)

Mn2+ + 2OH- --> Mn(OH)2(s)

Ni2+ + 2OH- --> Ni(OH)2(s)

Ba2+ + 2OH- ---> Ba(OH)2(aq)

Pb2+ + 2OH- --> Pb(OH)2(s)

With HNO3, all precipitates of OH- dissolved

2. With NH3, precipitate of,

Cu2+ + 4NH3 --> [Cu(NH3)4]2+ (deep blue)

is formed.

Ni2+ forms soluble [Ni(NH3)6]2+, [Ag(NH3]2]+ complex

the others did not form ammonia comples rather formed hydroxides.

3. The anions can be separated by first adding NaOH to form precipitates of hydroxides, filter and add HNO3 to dissolve precipitates and then test each ions.

From E)

1. Cations forming precipitate of sulfide with acid insoluble

Cu2+ + S^2- --> CuS(s)

Pb2+ + S^2- --> PbS(s)

Base insoluble sulfides

Ni2+ + 2OH- --> NiS

Fe2+ + S^2- --> FeS

Other Fe3+, Al3+ forms insoluble hydroxides

With NH3, complexes of,

[Ni(NH3)6]2+, [Cu(NH3)4]2+ are formed.

2. The cations are thus separated by adding first H2S under acidic medium, filter the precipitate formed and then basifing the solution and again passing H2S gas to form precipitate of other ions.

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