Development of a Reaction Matrix: What Are the Identities of the Unknown Chemicals?
Introduction
In chemistry it is often necessary to identify unknown substances. There are many procedures and pieces of equipment that can help a chemist to identify unknown substances, such as mass spectrometry or gas chromatography. While some of these methods and equipment are very complex and others are simpler, a common feature of each of these approaches is the comparison of properties of known substances with those of the unknown substances. Chemists can observe and compare physical properties of known and unknown substances, such as boiling point or density; likewise, it is possible to compare chemical properties such as how an unknown substance reacts with a known substance. One problem with testing and comparing physical properties of a substance involves solutions. It is possible that two different solutions will have the same density or even the same boiling point; in such a case those properties would not be helpful for differentiating between the two substances. In this situation, it may be more helpful to use observations of chemical reactions involving the unknown substance to determine what is in the solution.
An aqueous solution is created when a substance, the solute, is dissolved into water, the solvent. When different aqueous solutions are mixed together, it is possible that the substances dissolved into the water will undergo a chemical reaction, which may produce a precipitate. A precipitate is an insoluble ionic compound. Adding a few drops of an unknown solution to a powder may also cause a reaction, which might result in the formation of a gas. Other observable outcomes of a chemical reaction might be a change in color or a change in temperature. Since the chemical properties of a given substance are consistent when chemicals react with each other, the resulting products are also consistent and predictable; therefore, combining solutions together can be used as a way to identify them. This systematic process can be used to develop a table of reactions and their results, or a reaction matrix. If you know how specific known chemicals react with each other, it is possible to identify unknown chemicals by comparison.
Pre-Lab
1) What are the 4 observable signs of a chemical reaction?
2) Why is it not possible to see some of the chemicals dissolved in water when they are visible as solids? (for example salt is visible as a white solid but invisible when added to water)
3) If a solid forms as a result of mixing two solutions, what does it tell you about the attraction of the chemicals that formed the solid to each other compared to their attraction with water?(what were they more attracted to?)
4) Name the following and determine if they are solids or soluble.
a. Na2SO4 b. . SbCl3 c. HgO d. Fe2S3 e. Pb(NO3)2 f. Al2S3 g. PbI4
Your Task
You will be given seven labeled bottles to test and record data in order to generate a react...
