3.5: TA Notes
- Page ID
- 460986
\( \newcommand{\vecs}[1]{\overset { \scriptstyle \rightharpoonup} {\mathbf{#1}} } \)
\( \newcommand{\vecd}[1]{\overset{-\!-\!\rightharpoonup}{\vphantom{a}\smash {#1}}} \)
\( \newcommand{\id}{\mathrm{id}}\) \( \newcommand{\Span}{\mathrm{span}}\)
( \newcommand{\kernel}{\mathrm{null}\,}\) \( \newcommand{\range}{\mathrm{range}\,}\)
\( \newcommand{\RealPart}{\mathrm{Re}}\) \( \newcommand{\ImaginaryPart}{\mathrm{Im}}\)
\( \newcommand{\Argument}{\mathrm{Arg}}\) \( \newcommand{\norm}[1]{\| #1 \|}\)
\( \newcommand{\inner}[2]{\langle #1, #2 \rangle}\)
\( \newcommand{\Span}{\mathrm{span}}\)
\( \newcommand{\id}{\mathrm{id}}\)
\( \newcommand{\Span}{\mathrm{span}}\)
\( \newcommand{\kernel}{\mathrm{null}\,}\)
\( \newcommand{\range}{\mathrm{range}\,}\)
\( \newcommand{\RealPart}{\mathrm{Re}}\)
\( \newcommand{\ImaginaryPart}{\mathrm{Im}}\)
\( \newcommand{\Argument}{\mathrm{Arg}}\)
\( \newcommand{\norm}[1]{\| #1 \|}\)
\( \newcommand{\inner}[2]{\langle #1, #2 \rangle}\)
\( \newcommand{\Span}{\mathrm{span}}\) \( \newcommand{\AA}{\unicode[.8,0]{x212B}}\)
\( \newcommand{\vectorA}[1]{\vec{#1}} % arrow\)
\( \newcommand{\vectorAt}[1]{\vec{\text{#1}}} % arrow\)
\( \newcommand{\vectorB}[1]{\overset { \scriptstyle \rightharpoonup} {\mathbf{#1}} } \)
\( \newcommand{\vectorC}[1]{\textbf{#1}} \)
\( \newcommand{\vectorD}[1]{\overrightarrow{#1}} \)
\( \newcommand{\vectorDt}[1]{\overrightarrow{\text{#1}}} \)
\( \newcommand{\vectE}[1]{\overset{-\!-\!\rightharpoonup}{\vphantom{a}\smash{\mathbf {#1}}}} \)
\( \newcommand{\vecs}[1]{\overset { \scriptstyle \rightharpoonup} {\mathbf{#1}} } \)
\( \newcommand{\vecd}[1]{\overset{-\!-\!\rightharpoonup}{\vphantom{a}\smash {#1}}} \)
This page is directed toward laboratory teaching assistants, but is deliberately left open for students to read.
TA Notes
After completion of this module students will be able to:
- Use analytical techniques to create a serial dilution starting from pure, solid material. (Use an analytical balance, volumetric glassware, and pipettes)
- Use a full-spectrum UV-vis to measure the absorbance of a series of solutions.
- Determine the best wavelength to monitor the absorbance of an analyte.
- Validate a series of standard solutions using a control.
Pre-Semester Preparations
Do the following during the TA training and orientation week(s)
-
Check that the materials listed below are available and sufficient for all students to use them. If they are running low, please create more or inform the instructor.
-
Caffeine, 99%: There should be at least ~25 g of caffeine powder available. If not, please inform the instructor.
-
Volumetric Glassware: Be sure that there is sufficient glassware for four students to complete the experiment simultaneously. Please inspect the glassware for chips or obvious contamination. Clean or dispose of glassware as needed and inform the instructor if more glassware should be added to the lab space.
-
- Complete instrument training with Dr. Haas.
- Perform the entire experiment as if you were a student.
- Write and submit a report as if you were a student (this and the HPLC part of teh experiment).
- Practice grading your and your partner's report using the grading rubric.
Pre-Lab Preparations
When you are on TA duty, arrive at least 20-30 minutes early to prepare and ready the following materials for students.
- Check to be sure that caffeine powder is in its place (notify the instructor if we should order more).
- Check to be sure there are cuvettes available for students to use. They should be quartz cuvettes, not glass.
- Remind students to sign into lab
- Check that the student's pre-lab is complete
- Check their proposed calibration points and ensure that the control solution is approximately in the middle of their range.
- Tell students to gather their glassware as soon as they arrive and get set up on a bench space so that they can make solutions.
- They should clean their glassware prior to use.
- The Cary 100 UV-vis instruments (two of them) should be turned on at the beginning of lab period. Let the students be involved in this.
Helping your students
During the laboratory session, you are expected to be present and available for the entire 4.5 hours. Your job is to help students to complete the experiment safely and successfully, while upholding expectations and academic standards for the students.
In this particular laboratory session, please provide explicit instruction on the following:
- Weighing solid material: They can begin by weighing their caffeine when their glassware is clean. Please show students how to use the balances correctly and remind them that there is error associated with the measurement. (refer to P-chem materials…we assume that it is in the last digit of the reported number.) Show them how to quantitatively transfer their material into a volumetric flask, rinsing the weighing container into the flask with water.
- For using volumetric flasks: Remind them to use good technique. We can assume students know how to use these, but…..It takes a while to dissolve the solid material. DON’T LET THEM MOVE ON TOO QUICKLY! With powder in flask, fill it about 1/2 to 3/4 with solvent, swirl and sonicate as necessary to dissolve the solid before filling to the line.
Help students to analyze data immediately upon collection. They should validate their standard curve using a control solution. The control solution is provided, and it should be within the range of their calibration curve. If the control is outside their calibration range, a new control should be created. The students should treat the control as a sample in their calibration template, then compare their derived concentration to the known concentration. If the values are the same, then the curve is validated. If not, the students should re-create the standards using correct analytical technique. The students shold proceed to the HPLC module only after the calibration is validated.
Encourage students to proceed to the next module and begin creating methods for the HPLC if they have validated their curve and there is additional time in the period.
Shut down/ clean up
15 minutes prior to the end of the period, students should stop lab work and clean up. They are to leave the room in clean condition prior to the end of the period (17:55).
- Remind students when it is time to clean up.
- Remind students to save their samples!
- Turn off the UV-vis
- Remind students that all glassware should be returned to the storage locations.
- Any samples that are stored should be labeled clearly with the student's name and section.
- Remind students to sign out with the time they leave and get your signature.
- Check the TA checklist for additional items to be completed.