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UPDATE ON UNKNOWNS FOR THE SOILS ANALYSIS ASSIGNMENT
None of the unknowns have KCl in them this quarter.
Arlene Russell
Assignment 15 Report Guidelines
The report for this assignment will consist of a prelab that is due at the beginning of the first period, and a special analysis report form that is due at the end of the second period. the TA's will have this analysis form in lab.
Your prelab should include a title, reference, and date; a brief description of the procedure for each day; and the "Prelab Assignment" on page 127 of the lab manual.
IMPORTANT DATE CHANGE
A problem, possibly due to a reagent, has occurred in the Beer's Law analysis of iron for Assignment 11. We are trying to locate the source, the extent of the problem, and what sections may have been affected.
Until we have answers, I am postponing the report due date for Assignment 11 for one week. It is now due during your lab period on May 1 or 2. Further announcements will be made in class on April 24.
Arlene Russell
Chemistry 30L, Spring 2001
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: All questions are required for the first lab period; questions 1 – 2 only are required for the second lab period; no prelab assignment questions are required for the third lab period. Note: questions 3 and 4 are to be completed at the conclusion of the report. 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 and the data and observations are turned in at the end 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 must include
(a) Title of the experiment, date, etc.
(b) Reference to procedures. Note any changes in the referenced work.
(c) 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 ferrous ammonium sulfate, oxalic acid, potassium permanganate, 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 data
Weight 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 a proper 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
UV Spectrum Analysis
Using Beer’s law, determine the molar extinction coefficient for the iron complex (Note: You may assume that L=1cm.)
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.
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) Discuss reasons for the differences in the two numbers
Application:
Complete problem 3 and 4 from the study questions for period 2.