CHE151Lab6_IonicSolutions.doc CHE 151 Dr. Roderick M. Macrae CHE 151 General Chemistry Marian University, Indianapolis Lab 6: Color and spectra – what gives a colored solution its color? Name: Lab partner: Most objects do not emit light in and of themselves, but take their apparent color either from light reflected from the surface (opaque objects), or from light transmitted through the bulk (transparent objects). In many of our subsequent labs we will be using solutions of inorganic salts. These substances, like common table salt, are composed in their solid form of a three-dimensional lattice of ions held together by electrostatic forces. When dissolved in water, the positive ions (cations) and negative ions (anions) go into solution separately. Table salt (sodium chloride) is colorless, but many of these substances exhibit interesting and varied colors. The colors in solution typically originate in only the cation, though there are exceptions. Bring the handout CHE151SpectrophotometryF16.pdf with you to this lab. Objectives of this Experiment. (1) Prepare solutions of several inorganic salts of known concentration and note their colors. (2) Search for a relationship between presence or absence of color and position of the elements on the periodic table. (3) Use the Spectronic 20 spectrophotometer or Vernier SpectroVis to record an absorption spectrum for each solution. (Read the spectrophotometry handout beforehand.) (4) Determine the relationship between the shape of the absorption spectrum and the color of the solution. (5) Determine the relationship between the concentration of the solution and the intensity of the color. Precautions and Waste Disposal. Some of the compounds we are handling are moderately harmful. Wear your safety glasses, obey laboratory rules regarding food and drink, and wash your hands after any contact with the chemicals and before leaving the laboratory. Dispose of waste solutions in the containers provided, following the recommendations of the instructor. Procedure. (I) Preparation of solutions. Tap water already contains a large concentration of ions. For this reason, in all experiments where the exact composition of a solution is significant, we will use distilled water for the preparation of the solution. In order to take data quickly, we will work in groups and collate results at the end of the lab period. In some cases, solutions have been prepared beforehand; in others, it will be necessary for you to prepare a solution to the desired concentration.
CHE151Lab6_IonicSolutions.doc CHE 151 Dr. Roderick M. Macrae Note on units of quantity and concentration. Quantity: Since the mass of an atom is very small, a gram of a typical substance contains a huge number of atoms, ions, or molecules. Such large numbers are very unwieldy to use. For this reason, we use the unit known as a mole , with the following definition: a mole of a substance is
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- Fall '15