Chemistry 14CL Fall 2006 Report Guidelines for Determination of Iron in Vitamins Note: The Experimental Procedures for this Assignment are provided as a handout, which is available on VOH. The assignment is adapted from Experiments in General Chemistry, Principles and Modern Application, 8th Ed. Greco, Rickard, Weiss, Prentice Hall (2002) Pre-lab work (individual) (I) On-line Technique Videos and resources for this assignment A video on Beer’s law analysis is available at http://oid.ucla.edu/Webcast/Chemistry/ A discussion of the theory and practice of spectrophotometry and Beer’s law is given on pages 53-55 of your lab manual. You will work in pairs in this assignment. All data and observations should be recorded in each notebook. Only one postlab report should be turned in. (II) Introductory Report material. Be sure to include • The title and date of the first period of the assignment and your partner’s name and phone number • A reference identifying the procedure handout • A short introduction summarizing the goals of the experiment and the techniques that you will use during the first period of the experiment • A brief flow chart summary of the key procedures of the first period of the experiment • MSDS information for hydroquinone, o-phenanthroline • Data tables for recording the Beer’s law observations. Include columns for standard solution number or unknown solution, absorbance, transmittance, and concentration. In-lab work (I) Data and Observations: (this information should be in both lab notebooks) Record all your observations and the volumes you used for the dilutions. Complete the data table prepared in advance of lab. Post-lab work (group report) (I) Include one set of data in your post-lab report (II) Calculations: Follow the directions for the calculations given in the procedure. For Section A.2, make sure that you choose a scale for your graph that allows you to maintain the precision of your absorbance and concentration data in your calculations of the slope of the line. For Section A.3, determine the slope of the line of the standard calibration curve. Use this and the measured absorbance of diluted sample solution 3 to determine the ppm Fe (mg Fe/L) present in the solution. (III) Error Analysis The error analysis involves an estimate of the inherent error in the Beer's law plot.To calculate the error, first select the standard that most closely falls on the best straight line through your data. 1. For this point calculate the inherent error in • the absorbance measurement the manufacturer's stated reproducibility for the meter is +1% (absolute transmittance) • the volumetric solution used for this standard. 2. Convert the percentage errors to absolute errors. Place these error bars on the point on the line. Assuming that the error in the blank ("0") is small compared to the error in the standard, draw the maximum and minimum slopes possible for this standard line. 3. Determine the range of absorbances possible for the measurement of the aspirin-complex solution. 4, Project this range of absorbances on the maximum and minimum slopes in order to obtain the range of possible concentrations for your iron solution. Half this range is a reasonable estimate of the inherent error in the determined concentration.(see figure). XRange of XC(std) maxC(std) minA (std) maxA (std) minRange of A (unk)A b s o r b a n c e Concentration (IV) Conclusions Summarize your results. Compare your experimentally determined value for the weight of iron in a tablet to the value given on the bottle. If the difference is greater than your estimated error discuss other possible sources of
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