Unknown Chemical

Lead: Lead in solution can be detected by adding the chloride or iodide ion. Lead forms a white precipitate with chloride and a yellow one with iodide. The presence of lead must be confi rmed by adding chromate to another sample of the unknown; a brilliant yellow precipitate confi rms lead.Silver:You can check for silver in solution with a bright copper penny. Cover the penny with the unknown, if silver is present it will plate out onto the penny, turning it black.Cation Test: A common source of unknowns in school laboratories is the solutions of salts used in the laboratory experiment of fl ame spectroscopy to identify cations. The same technique used in this experiment can help identify unknowns. Oxidizer: Wet a piece of potassium iodide-starch paper with HCl diluted 1:3 with water and immerse in or touch to the unknown. If it’s an oxidizer the paper will turn blue-black. An alternate test is to mix the suspected oxidizer with fl our or sugar in a steel spoon as described in the fl ammable test. If the unknown is an oxidizer the mixture will burn much more vigorously than fl our or sugar by itself.Reducing Agents: Reducing agents such as sodium hydrosulfi te and formaldehyde will convert the yellow Cr+6 ion to the green Cr+3 ion. Add a slightly acidic solution of chromate or dichromate to the unknown and look for the color change.