Qualitative AnalysisDetermines only the presence (or absence) of a substance

Sometimes referred to as “Wet Chemistry”

Involves the identification of ions present in solution

Qualitative AnalysisGeneral idea is to separate ions into large groups first, then separate and identify within each group

Classic scheme has five groups

Group 1Includes Ag+, Pb+2, and Hg2

+2

ionsSeparated out as insoluble chlorides by adding 6M HCl

Group 1The

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

Group 1Then, the

liquid is extracted using a micropipette

Group 1The Ksp’s for each chloride are:

PbCl2 = 1.7 x 10-5

AgCl = 1.8 x 10-10 Hg2Cl2 = 1.2 x 10-18

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 1Once again,

centrifuge and separate the liquid from the solid using the micropipette

The liquid will be tested for the lead ion by adding K2CrO4

Group 1The solid

precipitate that remains will be treated with 6M NH3 with formation of a black solid confirming mercury(I) is present.

Group 1The liquid solution

from the previous step is tested for silver ion by acidifying with HNO3. The formation of a white precipitate confirms this ion.

Litmus TestsThroughout 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 2Separated 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.

C

S

H3C NH2

Group 3Separated 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 4Separated 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 greenCa = orange-redSr = crimson red

General UnknownLab final will include a General UnknownWill include one ion from EACH groupGroups 2 and 3 will be reduced to three ionsAfter 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