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Lab 2 Student instructions 2010(1)

Lab 2 Student instructions 2010(1) - Lab 3 Techniques and...

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Lab 3: Techniques and Measurement Fall 2010 A. Introduction 1. You need a protocol, done in two parts; one part for exercise C (preparing a stock solution) and the other part for exercise D (using the spectrophotometer and making a standard curve). See section D of these instructions and the introductory material in the lab manual for information on the protocol. Read the lab carefully and write a detailed protocol concerning the material and steps each section the lab. Include any calculations necessary for making solutions, figuring dilutions etc. You should be able to complete the lab referring only to the protocol. If you look at part C exercise 1 p. 42, you will see that there are 5 steps listed in making a solution and bringing the solution to a “final” volume. This is a basic protocol. Is it complete and do you understand it? Write out what you have to do and separate the questions so you can answer them as needed for the assignment. No credit for the lab unless you have a protocol for the exercises. B. General Teaching goals for this lab: 1. Achieve a basic level of competency in the use of the spectrophotometer and an understanding of its operation and application. Review the beginning of chapter 3 that covers the introduction to how the spectrophotometer functions. You do not need to know how to derive the formulas, but understanding the basic operation of the spectrophotometer instrument and the data generated is essential. For this you need to understand how light interacts with molecules in a solution, the “properties” Dr. Rappaport talks about. 2. Continue to develop what you began in the first lab, an understanding the nature of quantitative scientific investigation and inquiry; a combination of observations, hypothesis formulation and testing, gathering data, interpreting results and drawing conclusions about the observed phenomena. Of course, the job is not done until the paperwork is in, and written up for presentation. The first exercise on p. 42, in the lab is a review of solutions and will sharpen your skills in making solutions accurately, a necessary skill for the remainder of the semester in lab. The remaining exercises in the lab are designed to acquaint you with the spectrophotometer, its use and basic lab techniques. While doing this, you will investigate the relationship of a solution’s chemical composition and concentration to its ability to absorb or transmit light energy. What is a spectrophotometer? How does its ability to measure light allow you to estimate the concentration of a solute in a solution? What is the relationship between Optical Density (O.D.) you measure and the concentration of the solution? Organizing and recording your data in a table is important, but strictly accounting. Visualization of Data is an important part of a scientific inquiry as it allows you to see a relationship in the data that might not be easily discernable from a table. To visualize the relationship between O.D. and concentration, you will graph your data from the lab. A graph shows you a lot about that relationship for your results, or lack of one
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