CHEM 133 – Introduction to Qualitative Analysis Summer 2003 Dr. Jen Sorensen office: Bannan 504 phone: 296-5411 e-mail: sorensj1@seattleu.edu office hours: Monday & Wednesday 10:00-10:30AM Tuesday & Thursday 1:00-2:00PM Lab times: Monday and Wednesday 1:15 – 5:00 PM. For the first week of class only, labs will meet on Tuesday & Thursday (introduction to lab on Monday, no lab on Wednesday). Due to the extremely compressed summer schedule, absences are strongly discouraged. There are no scheduled make-up lab periods. Prerequisites: Satisfactory completion of CHEM 122/132. Co-register CHEM 123. Lab text: Introduction to Semimicro Qualitative Analysis, 7th ed., Lagowski & Sorum. Supplies: copy-page lab notebook fine-point permanent marker (such as a Sharpie) NO shorts or sandals
closed-toe shoes ankle-length pants goggles
Introductory remarks: The CHEM 133 lab experience is unlike the first two laboratories in this series. You will primarily work alone in this lab an you will be responsible for setting your own pace and drawing your own conclusions from your data and observations. Your grade will be determined in large part by your results. It is essential that you arrive in the laboratory prepared and organized for the experiments, otherwise you will waste valuable time and commit blunders. In addition, lab closes promptly at 5:00 PM. For the bulk of the quarter, you will conduct qualitative analysis experiments to determine the presence or absence of metal cations in solutions (“the qual scheme”). First, you will find it very helpful to react known samples of individual cations so that you can observe positive test results. Then you will perform the same test reactions on a sample containing unknown cations. This method will allow you to identify which cations are present and absent. After exploring three qualitative groups separately, you will be given a “General” unknown, which may contain cations from any of these groups. Laboratory notebooks and reports: A. Prelabs Headings: Name, date, experiment. Objective: One sentence describing the objective of the experiment. Methods: Flow chart format - indicate reagents, but not quantities. Also show reactions. The goal of this section is to express the essence of the chemistry going on in the experiments. Safety: Indicate any laboratory safety concerns.
B. In-lab observations Good record keeping is essential to success in this lab. It will aid you in interpreting your data and will help you remember what you did and observed. Remember, you will need to review your observations to make conclusions about your unknowns, so your in-lab notes need to be accurate, understandable, and painfully explicit. Keep careful record of your experiment and observation. A two-column approach is recommended for in-lab notes: Procedure and Observations. In one column indicate “What I did” and in the other column indicate “What I saw”. KEY: Write down what you actually did, not what the book says to do. KEY: Write down observations at each step along the way, not just at the end of a test. C. Results, discussion For the qual experiments, write a comprehensive discussion section that includes the following: For each cation present or absent, give a brief recap of all data that contribute to your knowledge of the presence or absence of each cation, including comparison with the known sample. You must report on more than just the final confirmatory test! Also mention any anomalous results that you observed. Note: Each qual report should also include a result form stapled to the front of the discussion write-up. Write the report narrative before filling out a result form. Sample conclusion for qual scheme write-up:
In order to write your report, you must begin by reviewing the flow chart and information provided in Lagowski – compare the text with your observed data. For example, your text might show the following for the three cations A+, B+, C+. A+ (aq) , yellow B+ (aq), colorless C+ (aq) blue
Na2S
A2S (s), green
B2S (s), white
C2S (s) black
Say that your observed data shows the following: Initial solution of cations was pale yellow and the first precipitate was rather gray. Your conclusion might read: “The initial solution was pale yellow; this is consistent with the presence of A+ and B+ and would seem to indicate the absence of C+. In the first precipitation a grayish/white precipitate was observed; this could be a combination of A2S, B2S, and C2S, but experience has shown me that the presence of a black precipitate usually can overwhelm the others so that the white and green might not be observed at all. Therefore, I suspect that only the A2S and B2S are present and the mixture of the green and white precipitates looks gray. This is consistent with the presence of A+ and B+, and absence of C+. Your discussion would go on to include a similar evaluation of each step in the separation procedure. You may choose to organize your write-up either chronologically (through the flow chart) or by ion. In some experiments colors are not helpful, but the important observations might include: the amount of precipitate formed, or amount dissolved under certain conditions such as during heating.
Grade: Your grade will be assigned out of 180 points, based on the following: Experiment Silver Group Al-Nickel Group Copper-Arsenic Group General Unknown Kinetics Pre-lab 3 4 4 4 4 Results 6 14 12 30 Observations 5 8 8 10 5 Discussion/Conclusions 6 14 12 20 11
Recommendations: Students who have taken this laboratory previously offer some suggestions.
1. Be prepared for lab by understanding the experiment; it wastes valuable time in lab if you are not ready, and since you are evaluated on the accuracy of your results, it is important that you know what you are doing. 2. Write down EVERYTHING and include sketches if helpful; observations are crucial; make interpretations about each of your experiments at the time you make the observations. 3. Label every test tube that you use as to its contents. 4. The tests for bismuth and aluminum can be particularly difficult. ALWAYS run a known at the same time as a control for the exact conditions. 5. REREAD all observations and interpretations before turning in results and conclusions. 6. If you have trouble discussing evidence and drawing conclusions, have someone in the Writing Center review your conclusions. This review is not done to correct grammar, but instead, to assist you in drawing conclusions from the observed data. It can be very helpful. 7. Do not fall behind schedule.
Lab Schedule: Date To Do Mon. 6/23 Pre-lab lecture: Intro to qual labs Tues. 6/24 Ag group known Ag group unknown Al-Ni group known Thurs. 6/26 Al-Ni group known Al-Ni group unknown Mon. 6/30 Finish Al-Ni group Cu-As group known Wed. 7/02 Kinetics Experiment Cu-As group Mon. 7/07 Cu-As unknown Wed. 7/09 Finish Cu-As group General unknown Mon. 7/14 General unknown Wed. 7/16 Finish general unknown Check-out Thurs. 7/17
To Read Syllabus Lagowski Chpts. 7, 8, 9, 11 Lagowski Chpt. 11 Lagowski Chpt. 10 handout
To Hand In
Ag group pre-lab Al-Ni group pre-lab* Ag group post-lab
Lagowski Chpts. 9-11
Cu-As group pre-lab Kinetics pre-lab Al-Ni group post-lab Kinetics post-lab General pre-lab Cu-As group post-lab
General post-lab due @ 10:45 AM
*You must hand in a pre-lab writeup for a group before proceeding with its experiments. It is recommended that you prepare pre-labs ahead of schedule so that you may begin a new group as soon as you finish the previous one.
Pre-lab Notes: Introduction to the Qual Scheme To prepare for tomorrow, read in Lagowski: Chpts 7, 8 – skim for general prep 9 – for silver group (group I) 11 – for aluminum-nickel group (group III)
Prepare groups I & III pre-labs (two separate pre-labs!!) according to this format: Heading Objective Methods Safety Helpful hints: Make a Xerox copy of the Lagowski group scheme (see page 171) so you can follow it while reading a procedure on a different page. terminology you will use repeatedly: o precipitate – solid product. Shorthand “ppt” o decantate – pronounced de-CAN-tate – liquid component of a hetero mixture. Gets “poured off” after centrifuging. Be organized!! Label everything. Set up some “standing beakers”: o hot water bath (tap water OK) o reagent water (distilled) ~ maybe one cool and one warm o waste jar Check the identity and molarity of each reagent before you squeeze it into your tube. Conc. strong acids and bases will be in the hood. Litmus: BRB, ABR