3. The hypothesis can then be tested by experiments designed to collect more data about the problem.

Transcription

1 University of Puget Sound Department of Chemistry Experiment 1 Chem 110 OBSERVATIONS-DESCRIBING WHAT CAN BE SEEN LABORATORY OBJECTIVES AND ASSESSMENTS 1. Be conversant in the use of laboratory notebooks as a scientific technique. a. Record pertinent observations at an appropriate level of detail. b. Organize observations in a tabular way that highlights patterns or trends. c. State the steps in the scientific method as described in this document. d. Describe criteria distinguishing observations and interpretations. 2. Develop safe laboratory skills. a. Demonstrate appropriate practices regarding safe handling of dilute laboratory reagents, organic solvents, and liquid nitrogen. b. Demonstrate the use of your senses for observing the results of laboratory experiments (e.g., to determine whether a gas is evolved). INTRODUCTION On a daily basis we run into problems that require us to make decisions. Sometimes the solution to a problem involves observing, collecting and analyzing data before making a decision. For example, if you drive a car, it is likely you observe and collect gasoline prices (data) and compare the prices (analysis) before deciding where to buy gas. This process of collection and analysis of data is a natural consequence of our mental ability to reason. The process of data collecting and analysis is also practiced regularly by chemists and other scientists. Scientists have developed a systematic method for making observations, collecting relevant data, analyzing the data and drawing conclusions from the analysis. This process, called the scientific method (see text), can be briefly summarized as follows: 1. First, observations are made, providing the scientist with data. If a set of observations is highly reproducible without clear exception, and deemed important, it may be elevated to the status of a law. 2. Based on initial observations, a reasonable question is posed related to a problem or unexplained observation, and a tentative explanation, or hypothesis, is proposed. 3. The hypothesis can then be tested by experiments designed to collect more data about the problem. 4. If the hypothesis is inconsistent with the new data then the original hypothesis is revised or discarded as needed. Further testing leads to more modifications. Eventually, the modified hypothesis may be elevated to the status of a theory. Observations Describing What CAN be Seen 1

2 The questions that are of interest to chemists often deal with the fundamental nature of matter. What is this stuff made of? Is this stuff going to melt in my hand or in my mouth, and why? Does this object have a greater mass than that object? If so, why? OBSERVATIONS VS. INTERPRETATIONS To answer these questions that arise in chemistry we make observations of phenomena in order to collect enough information to explain the cause of the observations. In the Chem 110 laboratories you will be learning to make observations so as to collect different kinds of data needed to address different types of problems. A simple observation is different than the interpretation (the explanation of the cause.) For example, an observation would be that something would melt in my hand or in my mouth, and to speculate on why it would melt is an interpretation. See the following table for further ideas to differentiate between them. Table 1. Observations vs. Interpretations (adapted from Heikkinen, H.W JChemED Vol. 87 No.7 pp.681 July 2010.) Observations Interpretations In the world In the mind Data/facts Ideas/hypotheses/theories Real Imaginary Hands-on Minds-on Correct/incorrect Useful/not useful Lasting Subject to change In this laboratory a number of procedures will be performed and observations made on each procedure. Follow the directions for each process. Observe what occurs and write down (in your laboratory notebook) a description of what you see. Do not give an interpretation of your observation. It is not necessary to know exactly what the chemical reagent is to make a valid observation of a reaction nor is it required that you use scientific terminology. Be sure to use words and terms that will make sense to you. Observations Describing What CAN be Seen 2

3 EXPERIMENTAL PROCEDURE WORK with a Partner Note: The experiments can be done in any order. Use your time efficiently and do not wait for reagents being used by another group. DISPOSAL AND SAFETY: Except for Exp. D, the liquid products in all reactions are rinsed down the drain and the solid products are placed in the trash. Note: The products of Exp. D are to be put in labeled Waste container in the hood. EXPERIMENT A Small snap-cap vial, Solution A-1 (copper sulfate solution), Solid A 2 (steel wool). 1. Place about 3 ml of Solution A-1 in the vial (the dropper barrel is graduated and the line just below the bulb is the 1 ml mark). 2. Place a small amount of Solid A-2 in the vial and snap the cap on the vial. 3. Shake vigorously (keep your finger on the cap of the vial). 4. Observe and record the results periodically for the following 30 minutes to an hour. 5. When there is no further change of Solid A-2 drain the liquid and transfer the solid to a piece of filter paper to examine it further. Record observations. EXPERIMENT B 12 well reaction plate, Solution B-1 (copper sulfate solution), Solution B-2 (sodium bicarbonate solution) 1. Place about 2 ml of Solution B-1 in one well of the reaction plate. 2. Add two ml of Solution B-2 to the same well. 3. Stir with the glass stirring rod. 4. Observe and record the results. 5. A few more drops of B-2 may be added to see if any other changes may occur. 6. Using a stirring rod or a spatula, place a drop of the product on a piece of filter paper to examine it further. Record observations. EXPERIMENT C 12 well reaction plate, Solution C-1 (saturated calcium acetate solution), Solution C-2 (95 % ethanol). 1. Place about 5 drops of Solution C-1 in one well of the reaction plate. 2. Add, with a continuous squirt, a full ml of Solution C-2 to the same well. 3. Observe and record the results. Observations Describing What CAN be Seen 3

4 4. Put the solid on a piece of filter paper to examine it further. Record observations. EXPERIMENT D 25-mL condiment cup, Solid D-1 (contents of a diaper), distilled water, Solid D- 2 (Table salt). 1. Place just enough of the powder D-1 (a small pinch), to sparsely cover the bottom of the plastic cup. 2. Add distilled water, 2 ml at a time and mix well until you have added about 10 ml. 3. Observe and record the results. 4. Wait a few seconds. Carefully turn the cup upside down. What happens? 5. Add a small amount of salt and mix. 6. Observe and record the results. 7. Dispose of products in labeled waste beaker in the hood. EXPERIMENT E MATERIALS: 50-mL graduated cylinder, 10-mL graduated cylinder, Solution E-1 (aluminum sulfate solution), Solution E-2 (sodium bicarbonate solution), Solution E-3 (dishwashing detergent). 1. Place 10 ml of Solution E-2 in the 50-mL graduated cylinder. 2. Add about 10 drops of solution E-3 to the liquid in the cylinder and gently mix. 3. Place 10 ml Solution E-1 in the 10-mL graduated cylinder. 4. Quickly pour the 10 ml of Solution E-1 into the larger cylinder. 5. Observe and record the results. EXPERIMENT F Copper pennies, Solution F-1 (Taco Bell taco sauce), paper towels. 1. Fold the paper towel in half and place on the table. 2. Place the penny on the towel. 3. Add a few drops of Solution F-1 on the layer of solid on the penny. 4. Rub the solution on the penny with your fingers. 5. Wipe off the penny with a paper towel. 6. Observe and record the results. Caution: Wash your hands and Do Not rub your eyes. Keep the pennies. The paper towels are placed in the trash. Observations Describing What CAN be Seen 4

5 EXPERIMENT G 12 well reaction plate, Solution G-1 (acetic acid solution), Solution G-2 (universal indicator), Solution G-3 (sodium hydroxide solution) 1. Place about 3 ml of Solution G-1 in one well of the reaction plate. 2. Set the reaction plate on a white surface (A piece of white paper can be placed under the reaction plate.) 3. Add about 1-2 drops of solution G-2 to the liquid in the well and gently mix with a stirring rod. 4. Observe and record the results. 5. Add Solution G-3 dropwise to the mixture in the well plate. Be sure to stir and make observation at each addition. Continue until there are no observable changes. 6. Place about 3 ml of Solution G-3 in another well of the reaction plate. 7. Add about 1-2 drops of solution G-2 to the liquid in the well and gently mix with a stirring rod. 8. Observe and record the results. 9. Add Solution G-1 dropwise to the mixture in the well plate. Be sure to stir and make observation at each addition. Continue until there are no observable changes. 10. Observe and record the results. ANY TEMPERATURE CHANGES YET? EXPERIMENT H Solution H-1 (sodium bisulfite solution with starch indicator), Solution H-2 (potassium iodate solution), distilled water, 2 50-mL plastic cups. 1. Place about 2 ml of Solution H-1 in one 50-mL plastic cup and add the same amount of distilled water. Mix with stir rod. 2. Set the reaction cup on a white surface (A piece of white paper can be placed under the cup.) 3. Add about 2 ml of solution H-2 to the other plastic cup and add the same amount of distilled water. Gently mix with a 2 nd clean stirring rod. 4. Pour the contents from the plastic cup into the liquid into the other cup and mix thoroughly with a stir rod. 5. Observe and record the results. EXPERIMENT I 12 well reaction plate, Solution I-1 (sodium hydroxide solution), Solution I-2 (hydrochloric acid solution), and Solution G-2 (universal indicator). Observations Describing What CAN be Seen 5

6 1. Place about 2 ml of Solution I-1 in one well of the reaction plate. 2. Add about 1-2 drops of solution G-2 to the liquid in the well and gently mix with a stirring rod. 3. Observe and record the results. 4. Add about 2 ml of Solution I-2 to the plastic cup. 5. Pour the contents from the plastic cup into the liquid in the well plate and mix thoroughly with the stir rod. 6. Observe and record the results. EXPERIMENT J 12 well reaction plate, DI water, Solid J-1 (ammonium nitrate). 1. Place about 2 ml of DI water in one well of the reaction plate. 2. Add about four pinches of Solid J-1 to the liquid in the well plate. 3. Mix thoroughly with the stir rod. 4. Observe and record the results. EXPERIMENT K NiTi (Nitinol ) wire (straight and bent in shapes), 2 crucible tongs, liquid nitrogen, Styrofoam bowl. NOTE: Liquid nitrogen is extremely cold (-196 C). Do not allow it to come in contact with skin or clothing, as severe frostbite may occur. 1. Try to bend the straight piece of wire. Record your observations. 2. Grasp the two ends of the straight wire with the two crucible tongs, and place the wire into the Styrofoam bowl containing the liquid nitrogen. After a couple of seconds in the liquid nitrogen, try to distort the wire. Place the wire on the bench top and observe what happens. 3. Take one of the provided shaped pieces of wire and carefully record your description of this wire with a sketch. 4. Grasp the two ends of the shaped wire with the two crucible tongs, and place the wire into the Styrofoam bowl containing the liquid nitrogen. After a couple of seconds in the liquid nitrogen, try to distort the wire. Place the wire on the bench top and observe what happens. Observations Describing What CAN be Seen 6

7 WHAT TO DO Before lab: BRING to lab Print a copy of this experiment, read it and bring it to your laboratory class. Bring your Lab Notebook with the PreLab assignment completed. The lab notebook can be purchased during the week for $15.00 (check to: U.P.S. or cash-correct change appreciated) from SAACS or the Chemistry Administrative Assistant. Bring Goggles and appropriate footwear. Approved goggles are available in Bookstore. PreLab Assignment Before coming to lab: In Your Lab Notebook: 1. Reserve the first four pages for your Safety Map (page 1) and Table of Contents (pages 2-4). The Safety Map will be completed during lab. 2. Beginning on page five, fill in the "Title bar" to include the experiment #, title of experiment, your name, partner's name (in lab), date, lab section, and Course Assistant s (CA's) name. This information should be included on each page in your laboratory notebook for all parts of every experiment. 3. Beginning on this same page five, below the Title bar, set aside a half page for each experiment. Separate the sections of the pages with the experiment titles, one at the top of the page and the next-half way down the page. Use the space below each Experiment title to record your observations during lab. In lab: 1. Complete the Safety Map on Page Think about what type of data you might collect. Some famous chemists used all their senses (sight, hearing, touch, taste, smell) in making their observations, but this adversely affected their life expectancy. In particular, don t try to taste any chemicals and don t dip your fingers into them. But you can use your: EYES (Vision) to see colors, cloudiness, bubbles, smoke, flames, speed of reaction, etc. EARS (Hearing) to detect explosions (unlikely in this lab). FINGERS (Touch) to sense any temperature changes in the bottom of the reaction well-plate. NOSE (Smell) to smell odors produced. 3. Carry out the reactions as described. (The experiments do not need to be completed in alphabetical order.) For each experiment, record all your Observations Describing What CAN be Seen 7

8 observations in your laboratory notebook in a systematic way, before proceeding to the next experiment. Clean up area and prepare for post lab discussion. At Home Be Next Lab: 1. Carefully examine the data in your notebook to see if you can come up with any system to organize the experiments into groups which have something in common. Some experiments may fall into more than one of these groups or categories. The experiments that gave similar observations could be grouped together, under appropriate, descriptive headings. (See example table.) 2. Condense your observations into a summary table in your notebook. Reproduce the example table (leave the observations blank) below BUT using a FULL PAGE and PORTRAIT orientation in your notebook. Your table will need enough rows for all experiments A- K. Table 1. Key Observations. Experiment Color Cloudy Bubbles Temp. Physical State Odor Misc. Obs. A X-green X B X X-flame C X X X Etc. 3. Write the following question and the answer at the bottom of the page with the Table. Question Describe a criterion used to distinguish between observations and interpretations. TO BE TURNED IN UPON ENTERING LAB NEXT WEEK: Be sure the assignment is removed from notebook and stapled before coming to lab. 1. The First Page should be the page with your table of the experiments and the answer to the question. 2. The next pages will be all the copy pages that contain your Experiment observations, in alphabetical order. Observations Describing What CAN be Seen 8