Bottles Without Labels
You are hired as a lab assistant at a local company that has a small collection of chemicals. In the interview you are told you have simply maintain the stockroom, getting chemicals for people, ordering new chemicals, etc.
You come into work your first day and are surprised. The stockroom is scant, only nine big 55 gallon drums of liquid. The previous worker was a lazy chemist named Mark, who went off to be a professor somewhere. He had worked there for so long, he knew what was in each barrel, so he just removed the labels as an element of job security. (He was the only one who knew what was where)
So you are faced with nine 55 gallon drums, with no labels. You rifle through the drawers and find 9 pieces of paper with chemical names only (no formulas, bummer dude.) They are:
Sodium Hydroxide (1M)
Hydrochloric Acid (1M)
Sulfuric Acid (1M)
Acetic Acid (1M)
Calcium Hydroxide (Saturated)
Sodium bicarbonate (1M)
Distilled Water (55.5 M)
Sodium Bromide (1M)
Potassium Iodide (1M)
Your first job is to get the labels on the correct drums. You cannot just start mixing the 9 substances together, as some of the reactions will be violent and dangerous. You must test the chemicals is some other way. At NO time may you combine any of the nine reagents. Do it and you say goodbye to chemistry lab at JCC forever.
Week 1: You contract with the local community college to use their lab for a day. You have access to small amounts of the nine 'standards' (in labeled bottles) and you also have some magnesium solid, Ca(NO3)2 solution (1M), and Mg(NO3)2 (1M) solution and CuSO4 (1M) solution, and bleach. Your contact at the college suggests you try combining each of the 9 chemicals with these testing reagents. If you want a partner for this portion of the lab, you may have one. In week 2, you will be on your own, with no lab partner. Do not make any conclusions about 'reactions' from just when you add the solutions together. Observe and make conclusions only after you have stirred the solutions together.
After you have left the college, (week 1) you must write down (electronically) a procedure for determining the identity of the substances back in your lab. The procedure can be of any sort, as long as it is understandable to someone else in your lab. A flowchart type procedure might be good. Here is a screencast of how to make such a flowchart. You will show this to your instructor at the beginning of the second week of lab.
Week 2: Back at work now (with no partner) You took a small amount of each of your testing chemicals back with you, but did not bring any of the standards. You are faced with the 9 drums. Perform small scale tests to confirm the identity of the 9 substances. You must give proof of each assignment. Your proof cannot be based on the identities of the other drums, each conclusion standing on its own merits. There is a small chance that you do not have 9 different substances (For example, 2 of the drums might be sodium hydroxide) Your report must give a coherent description of your procedure. (the one you wrote up for week 2) The report must also include nine paragraphs that start with "The identity of drum ___ is ... because ....." Describe in detail the observations you made to support your conclusions.
As with any other lab in CEM 141, you need to comment on this lab in terms of a learning experience and give at least one suggestion as to how to improve the experience.
Pre-lab questions (on a separate piece of recycled paper)
1. Determine the chemical formulae for each of the nine chemicals. Review the MSDS sheets for three of them (NOT water) and briefly describe the hazards.
2. Dream up a data sheet for your experiments the first day at the college. Simply recording observations on a blank sheet of paper will be very confusing and make your life miserable. Table? Flow chart? Tea leaves?
~MEO 11.29.05 10:33