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UCLA CHEM 30AL - Guidelines

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Chemistry 30ALSpring 2004Chemistry 30AL Spring 2004 Report Guidelines for Assignment 11, Synthesis and Analysis of an Iron Oxalate Salt Note: Three periods have been assigned for this experiment. Two days are scheduled for the analytical procedures. – one for the titrations and one for the colorimetric and UV measurements. Prelab Assignments: General comments: The prelab assignment questions are to be written in the lab notebook. They are due at the beginning of each lab section. Assignment 11: Prelab ‘Period 1 questions are due for the first of the assignment; prelab ‘period 2’ questions 1 and 2 are required for the second lab period; prelab ‘Period 2 questions 3 and 4 are required for the third lab period. . All prelab assignments are to be written in your lab notebook and are due at the beginning of the lab section. Lab Report General comments: Reports are written at three stages of the experiment. The introductory material, which constitutes preparation for lab, is completed before the lab starts. Data and observations are completed during the lab section. Both the introductory material andanswers to the prelab assignment questions are due at the beginning of the lab period. the data and observations are turned in at the beginning of each lab period. The final sections (data analysis, error analysis and conclusions) are completed after the lab period and are generally due one week after the experiment is complete. All work is to be written in the lab notebook. Every page must include the experiment title, the date, and your name. Assignment 11: Introductory material for each class must include (a) The title of the experiment, date, etc. (b) A reference to procedures. Note any changes in the referenced work. (c) A brief description of the purpose of the assignment and the techniques used in the experiment to fulfil that goal. (d) A flow chart for each day outlining the experiment procedures to be completed that day. (e) MSDS information on new chemicals to be used that day. Include the product name, chemical formula, formula weight, melting point or boiling point, and density (also known as specific gravity). Also summarize in your own words any health hazard data along with appropriate spill and disposal procedures. Period 1: ferrous ammonium sulfate, oxalic acid Period 2: potassium permanganate Period 3: bipyridyl Data and Observations must include: Period 1 (Start a new page each day; make sure the date is on each page) Reagent quantities used, observations at each step and after each reagent is added, weight of product (this may be obtained in period 2) Period 2 Weights of product used in titrations, exact concentration of KMnO4, titration volumes Period 3 Weight of product used in making standard solutions. Volumes and dilutions used for unknown solution Concentrations and volumes used to make standard colorimetric solutions. Colorimetric dataWeight and volume used to make standard solution for UV analysis. Data Analysis Synthesis: Calculate the yield of crude FeC2O4 that you obtained. Titrations Calculations: Determine the moles of oxalate in each of your titrations, based on the stoichiometry of equation 3, p. 98 (ii) Determine the moles of oxalate/gram of product for each titration Error Analysis: (i) Calculate the % inherent error for the moles of oxalate/ gram of sample for ONE of your titration trial. (ii) Calculate the % relative average deviation for the moles of oxalate/gram of sample that you obtained from the 3 trials. Note: Assume the % RELATIVE error in the stock potassium permanganate solution is ± 1% Colorimetric analysis Graph: Prepare a Beer's Law plot of absorbance vs. concentration for the standard solutions Your graph must have aproper title, labels, scales, etc. Data points must be clearly marked. Make sure the grid of your graph paper, or computer program allows you to determine the concentration of the solutions to ±0.5%. Calculations: (a) Determine the slope of the line (with proper units) (Indicate which two points on the line you used for calculating the slope). (a) Determine the concentrations for all the standard solutions (b) From the calculated slope of the line and the absorbance of “solution B”, determine the concentration of iron in “solution B” (with proper units) (c) Calculate the experimental molecular weight of your product (d) Calculate the moles of iron/gram of product Error Analysis (a) Determine the error in the concentration of ONE standard solution (b) (Identify all terms; place error bar on the graph) (c) Calculate the error in absorbance for ONE of the standard solution (d) (Identify all terms and place the error bar on the graph) (e) Calculate the range of possible slopes of the standard line. You MUST show clearly indicate the maximum and minimum slopes on the graph) (f) Determine the error in absorbance of your “solution B” unknown, and from that the error in the concentration of your “solution B” unknown (g) Calculate the % inherent error for unknown solution B Note: Assume the % relative error in the stock iron(II) sulfate solution is ± 1% Molecular Formula Hypothesis (a) Calculate the ratio of moles of oxalate/gram of sample (determined from the titration analysis) to moles of iron/gram of sample (determined from the colorimetric analysis) (b) Write a formula for the iron-oxalate complex that is consistent with this ratio (c) Determine the number of potassium ions required to neutralize the charge in the complex based on your result from the ratio in (a). Explain your reasoning. (d) Propose a molecular formula for the complex neutral salt that you prepared.UV/vis Spectrum Analysis Using Beer’s law, determine the molar extinction coefficient for the iron complex at the wavelength that corresponds to the maximum absorption. (Note: You may assume that the cell length is 1cm.) Conclusions: Discuss reasons why your yield was not 100% for the iron oxalate salt. For your titration data compare the % RAD with the % inherent error. How does this affect the calculation of the molecular formula \ of the compound? How does the error in the colorimetric analysis affect the prediction of the molecular formula of the compound? (i) Calculate the % difference in your experimental molecular weight (the weight that contains one mole of iron) and the molecular weight for the compound you are proposing. (ii)


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UCLA CHEM 30AL - Guidelines

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