Qualitative Analysis Determines only the presence (or absence) of a substance Sometimes referred to as “Wet Chemistry” Involves the identification of ions present in solution

Qualitative Analysis General idea is to separate ions into large groups first, then separate and identify within each group Classic scheme has five groups

Group 1 Includes Ag +, Pb +2, and Hg 2 +2 ions Separated out as insoluble chlorides by adding 6M HCl

Group 1 The precipitate is then separated from the remaining liquid by first using a centrifuge.

Group 1 Then, the liquid is extracted using a micropipette

Group 1 The Ksp’s for each chloride are: PbCl 2 = 1.7 x AgCl = 1.8 x Hg 2 Cl 2 = 1.2 x Being the most soluble, the lead(II) chloride will dissolve fairly readily in hot water. Thus, we will add DI water and heat in a hot water bath to dissolve this compound.

Group 1 Once again, centrifuge and separate the liquid from the solid using the micropipette The liquid will be tested for the lead ion by adding K 2 CrO 4

Group 1 The solid precipitate that remains will be treated with 6M NH 3 with formation of a black solid confirming mercury(I) is present.

Group 1 The liquid solution from the previous step is tested for silver ion by acidifying with HNO 3. The formation of a white precipitate confirms this ion.

Litmus Tests Throughout the schemes, you may be required to add acid until the solution becomes acidic or base until it becomes alkaline. “Blue” litmus  pink = acidic “Red” litmus  blue = basic (alkaline) Correct method – use stirring rod – dunk in solution, then touch to paper.

Group 2 Separated first by precipitation as an acid- insoluble chloride. Includes the ions: Hg +2, Pb +2, Bi +3, Cu +2, and Cd +2 Sulfide source is Thioacetamide.

Group 3 Separated first by precipitation as an alkaline- insoluble sulfide. Includes the ions: Ni +2, Co +2, Mn +2, Zn +2, Al +3, Cr +3, and Fe +3. Also uses Thioacetamide, but under basic (alkaline) conditions. Group 3 also has individual confirmatory tests for each ion.

Group 4 Separated by precipitation as an insoluble carbonate. Includes the ions Ba +2, Ca +2, and Sr +2. Identification includes flame tests for each metal ion. Ba = pale green Ca = orange-red Sr = crimson red

General Unknown Lab final will include a General Unknown Will include one ion from EACH group Groups 2 and 3 will be reduced to three ions After precipitation of EACH group, you will need to save the liquid for the next group(s) Any mistakes may mean that you have to start over from the very beginning! You will have a total of three hours to complete both the written and general unknown sections