Qualitative Analysis

AP Chemistry Name_____________________Per ______

Qualitative Analysis of Cations

Analysis of Solutions Containing the Ions

Ag+, Pb2+, Hg22+

Qualitative analysis is an analytical procedure in which the question “what is present?” is answered. In a systematic qualitative analysis scheme, each substance present is separated from the other substances. Then a confirmatory test is used to prove that the isolated substance is the expected one.

In this experiment you will analyze a solution that can contain any combination of three different cations. First of all, you will prepare a solution that is “known” to contain all of the ions, and you will analyze this solution to learn the techniques for the analysis. Then you will analyze an “unknown” solution to determine which ions are present and which are absent. You may have one, two or all three cations in your solution.

This experiment is carried out on a semi-micro scale. Very small quantities of reagents are used. Cleanliness and a great deal of care are necessary to obtain good results.

Major Concept behind Qualitative Analysis:

Since it is impossible to visually identify the presence of ions (unless they are colored); generally a solution called as reagent is used to precipitate the desired ion. The presence of this precipitate will confirm the presence of the ion. Based on your solubility rules, could you identify a reagent for Pb2+ ions?

Note: Even though we talk of cations like Ag+, Pb2+, Hg22+, they are present as ionic compounds like AgNO3, Pb(NO3)2 etc. or acetates of these ions. Since NO3 –or acetate ions act as spectator, we do not consider them while mentioning these ions. It is impossible to get a cation without anion.

General Techniques for Qualitative Analysis

Keep Good Records

It is necessary to keep good records so that you will not get confused and forget what solutions are in which test tubes. Number your test tubes using blue tape if you take them out of...