Chemistry 14CL Winter 06 Amino Acid Analysis Experiment Post-lab Guidelines The post-lab report must be written inside your lab notebook (except graphs) This is a Group report (i.e. turn in ONE report per group) Before attempting to work on this group report, please take a moment and read the following tems carefully. Definitions of Group Report and/or Group Experiment (1) All members in the group MUST contribute equally when working on the experiment as well as writing the post-lab report (2) Each group member must be prepared ahead of time when writing the reports. This means review materials from lectures or from Chemistry textbook or from on-line resources on certain topics that are relevant to the concepts in writing the reports. Contribution to the group work is meaningless if the group member does not understand the concepts behind the experiment. (3) It is the responsibility of the group members to plan ahead on when they should get together to work on the report. In other words, maintain good communication between group members. (4) It is the responsibility of each group member to honestly describe the work that they did during the experiment and in writing the report. No one should take advantage of the other group member. Report to the course instructor or your TA if you feel that other group members are taking advantage of your work. (5) Each member in the group MUST understand the concepts behind the ENTIRE experiment regardless of which portions of the report or experiment the person are responsible for. This is especially important for the exams.Chemistry 14CL Amino Acid Analysis Experiment Post-lab Guidelines The post-lab report must be written inside your lab notebook (except graphs) This is a Group report (i.e. turn in ONE report per group) Refer to the lab schedule for the due date of this report Post-lab Report Guidelines (i) Write down the unknown serial number (ii) Write down the names of all the group members and their responsibilities in writing the report and during the experiment. (iii) Abstract - goal of the experiment plus a summary of your experimental results. (iv) Graphs (see lab manual (p.97) for the total number of graphs) (Use EXCEL or any other spreadsheet software for this part of the report) You may review how to plot various types of titration graphs from your 14BL post lab reports and the EXCEL workshop handouts from 14BL. Total Number of Graphs for the Amino Acid Experiment: (i) Expanded derivative graph for EACH TRIAL of NaOH/amino acid titration (ii) Expanded titration graph for EACH TRIAL of NaOH/amino acid titration (iii) ONE FULL titration graph for the determination of pKa’s (see page 93). Pick the best trial for the HCl/amino acid titration and the best trial for the NaOH/amino acid titration and combine them to ONE full titration graph. * When plotting the titration graphs, please keep in mind the followings. ♦ Correct scales and full use of graph paper ♦ Gridlines for proper readings of the scales ♦ Axes (labeled with units) ♦ Appropriate titles IMPORTANT: For the expanded graphs for NaOH/amino acid, you should print out EACH equivalence point region on a SEPARATE piece of paper for each trial. This is especially important for the expanded derivative graphs. You will run into problem when locating the equivalence point volumes if you combine both equivalence point regions on the same piece of paper. For any expanded titration graphs, you should plot no more than +/- 2.00mL around the equivalence point region. Make sure that the minor gridlines have a scaling of about 0.05mL for ALL the expanded titration and first derivative graphs. Chemistry 14CLAmino Acid Analysis Experiment Post-lab Guidelines The post-lab report must be written inside your lab notebook (except graphs) This is a Group report (i.e. turn in ONE report per group) Data Analysis (Make sure you use the calculated values for TRIS, HCl, and NaOH) * Concentration of primary standard (i.e, Tris solution) * Average Concentration of HCl * Average Concentration of NaOH * Average Concentration of unknown amino acid * Determine values of pKa1 and pKa2 for the amino acid unknown (Make sure you use the average concentration calculated for TRIS, HCl, and NaOH when calculating the unknown amino acid concentration) Error Analysis (Review concepts on error propagation from 14BL before you start working on the error analysis for this post-lab). SHOW ALL YOUR WORK ♦ %Inherent error in concentration of HCl solution determined from propagation of errors for ONE of your HCl/TRIS titration trials. ♦ %Inherent error in concentration of NaOH solution determined from propagation of errors for ONE of your HCl/NaOH titration trials. ♦ %Inherent error in unknown amino acid concentration determined from propagation of errors for ONE of your amino acid/NaOH trials. ♦ %RAD of unknown amino acid concentrations Conclusion ♦ Summarize results ♦ Comment on the precision of unknown amino acid concentration. ♦ Compare %RAD with % inherent error for the amino acid. What can you conclude? Error Analysis for the Amino Acid Titration ExperimentPropagation of errors is discussed in section III.4. of the lab manual page 23-27 (I) Error in the normality of HCl (Ma) ∆MaMa=∆MtrisMtris+∆VtrisVtris+∆VaVa=∆WttrisWttris+∆Vol. flkVol. flk+∆VtrisVtris+∆VaVa ∆Wttris = error in balance ∆Vol. flk = error in 100ml volumetric flask ∆Vtris = error in pipet ∆Va = Error in buret reading (II) To find the concentration of NaOH we used the formula Mb=MaVaVb therefore the inherent error in Mb is ∆MbMb=∆MaMa+∆VaVa+∆VbVb ∆Va = 2*error in pipet reading ∆Vb = error in buret reading (there is no graphing error since students are NOT required to plot the titration graphs for the NaOH/HCl trials). ∆Ma / Ma = expression derived in (I) (III) The concentration of the unknown amino acid can be calculated from,Munk = [Mb*(Vb2 – Vb1)] / Vunk where Vb2 and Vb1 are the two equivalence points for the NaOH/unknown titration The inherent error for the unknown amino acid is slightly different from (I) and (II) due to the subtraction term of the two volumes. ∆MunkMunk=∆MbMb+∆VunkVunk+∆Vb2(Vb2− Vb1)+∆Vb1(Vb2− Vb1) ∆Mb / Mb = expression
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