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Unformatted text preview: ble ion from the others. The soluble ion is separated by collecting the solid at
the bottom of a test tube in a ce ntrifuge , a device that creates a centrifugal force by rotation. After the
precipitate is compacted, the s upe rnatant (the liquid solution above the solid) is de cante d (carefully poured off)
into a separate container. The soluble ion is in the liquid supernatant while the insoluble ion is in the solid
precipitate. Thus they are physically separated from each other when the liquid is poured off, leaving the solid
behind. The solid precipitate is typically washed with water to help remove any traces of the soluble ions that
www.webassig n.net/ebooks/wsug encheml1/lab_5/manual.html 1/6 4/15/13 Lab 5 - Qualitative Analysis remain. This prevents "false positive" test results later on.
In order to devise a scheme for separating a mixture
of the cations in this lab, each ion will be tested individually for its solubility characteristics. You must carefully
observe the behavior of each ion under the test conditions described in the procedure. The presence or absence
of a solid and the accompanying colors of solids and solutions will provide important clues both for your
separation scheme and the eventual identification of the ions. Deviation from the procedure may give different
results, so be consistent in your technique.
When you think you have a particular ion isolated in solution, how
do you prove it? One way is to do a chemical test on the solution and show that the results of that test are
identical to those of a genuine sample of the ion. This type of confirmatory test forms the basis for identifying the
ions you think you have separated. A true confirmatory test is unique to a particular ion. In other words, the
presence of other ions will not give a false positive result. For the three cations in this experiment, the
confirmatory test will be based on the addition of iodide ions. You will observe the behavior of the three cations
in the presence of iodide, and then apply this test whenever you think you have isol...
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This document was uploaded on 01/22/2014.
- Spring '14