Chemistry Laboratory Waste Evaluation

Tracy D. Harvey, University of Washington

Summary

The 100-level (Chem 142, 152, and 162) post-laboratory manuals have been revised to include a request for an evaluation of the waste generated during each experiment. The students are asked to provide a list of the materials used and the products generated during the experiment, and also the chemicals remaining (as waste) after the experiment is concluded. The manuals ask the students to include an estimate of the amounts of each item listed. From the scientific viewpoint, this evaluation will help the students see a process instead of just a data collection event, and they will get to practice estimating amounts. They will also need to determine the products of any reactions performed during the experiment. From the standpoint of sustainability, this evaluation is intended to help the student recognize the environmental "cost" of an experiment-in consumables used and in waste products generated. The materials will end up either in the public water system, the air in the laboratory, the solid waste system, or in the hazardous waste streams that are established for the campus. The students may appreciate the small volumes of waste generated and the generally non-hazardous nature of these particular labs. Hopefully, this awareness will carry over into future experiments they pursue, helping to minimize the generation of laboratory waste, especially hazardous waste, whenever possible.

Learning Goals

Context for Use

Description and Teaching Materials

The 100-level (Chem 142, 152, and 162) laboratories are designed to be an integral part of the first year chemistry courses; it is required for the students to complete these laboratories to receive a passing grade for the courses. The laboratories are three hour sessions and are performed in pairs. The students complete a pre-lab assignment individually prior to attending lab; the pre-lab assignment is designed to familiarize the student with the activities being performed during the lab and the calculations they will need to do following data collection.

In lab the students work from the course laboratory manual and record necessary information into a laboratory notebook. Some materials are provided in the lab; other materials are checked out from a stockroom. Typically, bottles are provided to collect liquid wastes and instructions are given in the procedure for any waste treatment to be performed by the student. Non-hazardous aqueous wastes are generally poured down the sink and things like filter papers and plastic pipet tips are disposed of in the trash. Hazardous and non-aqueous wastes are collected in common waste containers; the contents of these common waste containers are disposed of by the scientific technicians who manage the laboratories.

The students complete a post-lab report at the end of each experiment; this report may be due in class or submitted at a specified later date. Most of the post-lab reports are Excel templates; these templates have text boxes and boxes for calculations. A new text box has been added to the post-lab reports. It reads as follows:

Laboratory Waste Evaluation (1 pt)

"Laboratory waste is considered anything generated during an experiment that is disposed of down the sewer drain, thrown in the garbage, collected in a container for disposal by the University of Washington Environmental Health & Safety department, or released into the environment. Based on the written lab procedure and your actions during the lab, list the identity and approximate amount (mass or volume) of waste that you generated while performing this experiment."

Teaching Notes and Tips

It is expected that the students will complete this list in 10-15 minutes. The evaluation is worth one point of a 60 point total possible. The answer will be graded in the spirit of "get it" or "doesn't get it". The teaching assistants are given a key, with the instruction that the waste list "should look something like...."

As an example, here is the information provided in the key for Lab #1 in Chem 152:

All or nothing - they don't have to be correct, but they have to have an answer. For this lab, the waste should look something like:

1000 mL water (this is ~900 mL for cleaning/rinsing glassware and ~100 mL for adding water to KHP in Part I)

140 mL NaOH (assumes ~20 mL for each KHP titration, 50 mL for the HAc titration (since they'll probably fill their buret), plus additional amounts for rinsing the buret and leftover NaOH they poured into a beaker for filling the buret)

1.5 g KHP (assumes 0.45 g KHP weighed out for each of the titraitons in Part I)

50 mL HAc (they're told to get ~50 mL in a beaker so that they can then use the volumetric pipet to obtain 25 mL for the titration)

0.5 mL phenolphthalein (assumes 0.05 mL per drop and three drops per titration of KHP)

0.1 mL thymol blue (assumes 0.05 mL per drop and two drops for the HAc titration)

1-2 pieces of pH paper for testing the waste

3 pieces of weighing paper for use with the KHP

They do not need to explain the amounts, but should have a list that includes 1000 mL water, 140 mL NaOH, 1.5 g KHP, 50 mL HAc, 0.5 mL phenolphthalein, 0.1 mL thymol blue, 1-2 pieces of pH paper, and 3 pieces of weighing paper. The explanations are for your benefit and to assist you with evaluating whether or not they are in the ballpark. If they are not in the ballpark, you can write something like "this is a low estimate" or "did you remember all of the rinse water?," but DO NOT deduct points for an incorrect estimate. This is simply an effort aimed at increasing awareness of what they are using and throwing away during the experiments.

Assessment

References and Resources

Evergreen State College