Week 5

Read pages 153 - 190 in lab manual.

Review lectures slides on solution preparation and conductivity meters (posted in D2L Week 5 Content).

Review textbook chapters 22, 23, and 24 as needed. 

Example of Tris buffer preparation: https://www.youtube.com/watch?v=S6bgIeM5wSQ

• Notes:

  • Similar methods to those in the video can be used to prepare any single solute solution. For a simple salt solution (e.g. NaCl), the pH may or may not be measured. For any buffered solution, pH measurement and adjustment are part of the preparation as shown in the video.

  • For multiple solute buffers (e.g. Tris buffer with electrolytes), dissolve all solutes thoroughly before measuring and adjusting pH.

  • Note that there are multiple methods for preparing buffers (i.e. adjusting with drops of HCl or NaOH as shown in video, or dissolving pre-calculated ratios of acid and base forms of a buffer molecule.)

Before class on Day 2:

• Read through CA #11 and CA #12 in the lab manual.

Before class on Day 3:

• Download the Week 5 Quiz (D2L Week 5 Content) and upload your answers (D2L Assignments).

LE #14, Part A and B (Preparation of single solute solution)

• Read through CA #11 and CA #12 as preparation. Refer to Updated Table 5.3 posted in D2L Week 5 Content. Obtain all chemical information listed in Table 5.5 (page 170) for the chemicals listed in updated table.

• Complete all calculations from Updated Table 5.3. After verifying calculations with the instructor, each student will be assigned one solution from this table to prepare for as part of LE #14 Part B.

• Review SOPs / manuals for conductivity meters before use.

• After completing all data for LE#14, submit your data from LE14 using the class data link in D2L, Week 5 Content.

LE #15 (Correlating conductivity to concentration of single solute solution)

• Protocol note: prepare 45 mL of each solution (in a 50mL conical tube), rather than the volume indicated in Table 5.7

• Each student is assigned one solution from Table 5.7 (page 179) - refer to LE15 class data link in D2L, Week 5 Content.

• Prepare the solution assigned and measure conductivity. Report your results using the LE15 class data link. Prepare a graph relating conductivity and concentration for all solutions prepared by the class.

• Document this as Entry #9 in Benchling. In your discussion section, answer questions 1c/d, 2, 4, and 5 on page 180-181.

Tris Buffer Preparation

• Refer to Tris Buffer Recipe Worksheet (D2L Week 5 Content).

• Complete the worksheet with your lab partner and thoroughly check your protocol and calculations with another group of students.

• Prepare your buffer according to the recipe selected, take all measurements, and have another group of students verify your buffer product.

• Document the results in Benchling using the "Batch Record (F2021 Template for Buffer Preparation)" rather than the typical lab notebook entry template.

Demonstrate your conductivity meter calibration technique and results to the instructor.

Use the Class Data links (D2L, Week 4 Content) to share your data from LE 14 and 15.

Entry for LE 15 to be completed this week.

The batch record entry can be left open until completing buffer preparation next week.

Using a different conductivity model at another equipment station, follow the SOP instructions and calibrate the meter. Take conductivity measurements of 1-2 unknown solutions. Verify that you can repeatably obtain accurate conductivity measurements. Troubleshoot your technique, equipment function, and impact of environmental variables when conductivity measurements vary.

Additional practice with pH measurements, conductivity measurements, and dilutions: https://docs.google.com/spreadsheets/d/1Xb8BaxiZnX2azcHVJEhBX9BuVyGU2xB4KWlnk7Sdo_A/edit?usp=sharing

On Day 1, you will have time to complete the Tris buffer preparation assignment, product verification, and batch record documentation. Use additional time in lab for practice with pH meters, conductivity meters, and and review of solute preparation and calculations.

At the end of the week, we will hold the second lab practical exam.