Intro To Qualitative Analysis Lab

Chemistry Lab: Introduction to Qualitative Analysis Objective:

Adapted from “Quick Qual” used by the UNO-CU Chemistry Field Day

Identify the positive tests for anions and cations. Identify the cations and anions present in a set of unknown samples.

Procedure:

The lab will be completed in two parts. In Part 1, you will identify the positive tests for samples in which the cation and anion are known. Record observations of the positive tests in your lab notebook. For the second part, you will identify the cation and anion present in each of five separate unknowns. Cations

Anions

Na+, K+, Ba2+, Li+, NH4+

CO32-, SO42-, Cl-, C2H3O2-, I-

Part 1: Positive tests for cations: Use the flame test technique to identify the sodium ion (produces a yellow flame), the potassium ion (produces a faint purple flame), the barium ion (produces a green flame) and the lithium ion (produces a red-fuchsia flame). The ammonium ion will not show a color in the flame test. Test for ammonium: Add 10 drops of 6M sodium hydroxide to 10 drops of the sample. A faint ammonia odor indicates the presence of the ammonium ion. Positive tests for anions: Carbonate:

Add 10 drops of 6M HCl to 10 drops of sample. Odorless bubbles indicate the presence of the carbonate ion.

Sulfate:

Add 10 drops of 6M HCl to 10 drops of sample. Next add several drops of barium chloride solution. A white precipitate indicates the presence of the sulfate ion.

Iodide: Add 10 drops of starch solution to 10 drops of sample. Then add 10 - 20 drops of hydrogen peroxide. A blue-black solution indicates the presence of the iodide ion. Chloride:

Add 10 drops of 1 N nitric acid to 10 drops of sample. Then add a few drops of silver nitrate solution. A white precipitate indicates the presence of the chloride ion.

Acetate:

Add 10 drops of 3M sulfuric acid to 10 drops of the sample. A vinegar-like odor indicates the presence of the acetate ion.

Part 2: Obtain a set of unknown solutions from the instructor. Record the code for the unknown in your lab notes. Proceed with the tests as in Part 1. Record the identity of the cation and anion in a table in your lab notebook.