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Name: Ann
Status: student
Age: 9-12
Location: PA
Country: N/A
Date: 12/29/2004

What is the purpose of testing for ions and cations? We completed an experiment for determining what ions and cations were present in solutions, but how does this relate to practical applications?

Hi Ann,

Working in the environmental field, I find it is very important to understand what anions and cations are present in polluted water. Knowing both the type and concentration of these ions helps me determine how to design a process which will remove them and make the water clean enough to return to the environment.

For instance, NaCl is simple table salt and seems relatively harmless. However, if there is a lot of chloride anion present, the water becomes corrosive to iron and steel piping and other mechanical equipment. Another common anion is fluoride. A small amount in drinking water helps prevent cavities; a large concentration can be fatal.

Common cations include heavy metals such as copper, nickel, zinc, lead, and chromium. If concentrations are too high, they can become toxic to fish and other aquatic species. So, it is very important to me that I am able to determine what anions and cations are present in a particular solution.

Bob Hartwell


Historically this kind of identification scheme was once the only way possible to identify the contents of an inorganic mixture. This is no longer the case, although the spirit of these kind of test is still very much alive and this kind of identification has many practical applications. Tests which detect the presence/absence of a compound are routinely used in forensic science (think CSI-they might need to know whether someone has gunpowder on their hands using a quick swab technique).

In chemistry class, there are two main purposes for the "qualitative ID" experiments that you did. One is to expose you to a lot of chemical reactions, which is good to do in a chemistry class because it helps you learn more chemistry. The second, equally important, reason is to improve your logic skills by having you use them in a practical context in the lab.

The chemistry that reveals the presence/absence of ions is very important. Some of these reactions control the formation of caves and cave formations and the pH of buffer solutions. Others determine where and whether certain minerals will form or redissolve. Still others are simply foundation oxidation/reduction reactions which occur in nature. Many of these reactions can be used to separate out undesired impurities from an environmental sample prior to subsequent analysis using instrumentation.

Regardless, the knowledge that you gain by unraveling these reactions and figuring out their net ionic equations is invaluable foundation work for advanced studies in chemistry and biology.

The logic skills that are necessary to develop your own identification tree are very important. This process of elimination kind of thinking is exactly the same that is used in forensics as well as many other applications. Sherlock Holmes once said the following: "When you have eliminated all which is impossible, then whatever remains, however improbable, must be the truth." -- The Blanched Soldier ( The branching logic of the qualitative ID scheme works exactly according to this principle. There are of course many other applications of this kind of skill (including all fields of scientific research, debugging computer programs, and deconstructing engineering design problems), but forensics is the one you will see on TV the most.

Hope this helps.

Dr. Topper

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