Lab Activity H4 It s Snow Big Deal OUTCOMES After completing this lab activity, the student should be able to use computer-based data acquisition techniques to measure temperatures. draw appropriate conclusions based on the results of a simple experiment. prepare a written report which accurately and succinctly conveys the information obtained in the experiment and the conclusions drawn as a result of it. DISCUSSION Living in Minnesota, we are used to the presence of large amounts of snow and ice in the winter and the subsequent salting and sanding of the roads. While we may be used to living with the consequences of salt on the roads and our cars, why do we dump all of that salt on the roads? How does it affect the temperature of the snow and ice? If the temperature of a liquid is lowered to a certain point, the liquid will begin to change into a solid, in a process we know is called freezing. We observe this every time we make ice cubes in the freezer. The temperature at which a liquid changes into a solid is called its freezing point. Every pure liquid has its own characteristic freezing point. What is the freezing point of pure water? What temperature must a mixture of pure ice and water be once it levels off? However, once impurities are added to a liquid, its freezing point will change. This is one example of a colligative property. If you ve discussed these properties in lecture, you should review them now so you may apply that knowledge toward the experiment. In this lab activity you will determine how the addition of various compounds to snow (or an ice/water mixture) will affect that mixture s temperature, and you will explain your results in terms of the freezing points of the new mixtures. While doing this, you will also learn how to use computer-based methods to gather data. Computer-based data acquisition techniques are used in upper division science courses, as well as in professional laboratories and other workplace settings. The primary advantage of computer-based methods in any laboratory setting is the speed with which data can be gathered. Computers also assist in data analysis and can improve the overall efficiency and accuracy of laboratory and business processes. To be prepared to work in any type of professional environment, you must be familiar with computer-based methods of data collection and analysis. In the laboratory, data-gathering probes are utilized when working with computer-based data acquisition techniques. Data-gathering probes are simple electronic devices that respond to different types of stimuli by sending out electrical voltage signals. The signals by themselves H4.1
may appear to have little meaning, but computer software can interpret and display the signals as meaningful data. In order for the software to correctly interpret the signals, however, it is necessary to calibrate the probe. Calibration consists of feeding the probe a signal of known value and teaching the software to recognize that value as a reference point. Some probes will already have a calibration file built in to the hardware and software. Other probes (like ph probes) require that the calibration be done manually. In this lab activity, a temperature probe will be used to record the temperature of snow (or ice water if there is not sufficient snow present) with and without various solids dissolved. Probes connect to the signal interface, which serves as a switchboard for routing signals into the computer, where the software interprets the signals. MATERIALS (Provided By Student) Bowl Computer with open USB port Ice Melt or Baking Soda (not baking powder)* - 8 g Salt - 8 g Snow or crushed ice (not ice cubes) - approx 500 ml Sugar - 8 g MATERIALS (From Kit) Go! Temp temperature probe with Logger Lite or Logger Pro software Electronic Balance Plastic cup Portion Cup, plastic cup, or folder paper Safety goggles/glasses *Please note that Ice Melt and baking soda are two different chemicals. Other sidewalk de-icers may also be used, but may be different chemicals than found in Ice Melt. Feel free to use whatever you have available Ice Melt, an alternative sidewalk de-icer, or baking soda. The most important part of this lab will be the observations made when the three different chemicals are added to snow or a crushed ice/water mixture. REQUIRED PHOTO: Includes the date clearly shown on a calendar, newspaper, cell phone, or written on a sheet of paper, along with all of the materials used in this lab. PROCEDURE SAFETY GOGGLES/GLASSES MUST BE WORN FOR THIS EXPERIMENT! 1. Collect approximately 500 ml of snow from outside into a bowl. Allow the snow to melt just enough to become moist before moving on to the next step. If no snow is available, crush enough ice cubes to obtain about 500 ml of crushed ice. 2. Plug the Go! Temp temperature probe into a convenient USB port on your computer and launch the Logger Lite application that was installed during Lab H1. The temperature probe should automatically be identified by the software and interface. 3. Under the Experiment menu, select Data Collection Set the collection mode to Time Based, the experiment length to 180 seconds, and the sampling rate to 0.2 H4.2
samples/second (5 seconds/sample). Check the box to take a Sample at Time Zero. If the settings were correctly done, it should read near the bottom of the window, Samples to be Collected: 37. 4. Place 100 ml of snow or crushed ice (not ice cubes) into the plastic cup. If crushed ice is used, add a small amount of water to the cup to moisten the ice, but not enough water to cause the ice to float on top of the water the ice should still touch the bottom of cup. 5. Plunge the temperature probe into the middle of the snow and immediately start the data collection by clicking the green Collect button on the Logger Lite tool bar. 6. Stir the probe in the snow until the experiment stops on its own after 3 minutes. Notice that the time and temperature readings are displayed on the data table and the points are plotted as the experiment runs. If needed, the data collection may be stopped early by clicking on the red Stop button. (NOTE: When data collection begins, the green Collect button becomes a red Stop button.) REQUIRED PHOTO: Includes your face and/or clearly shows a Picture I.D. (with name), with the temperature probe, cup with ice/snow, and the Logger Lite/Pro screen with your data in the background. 7. Examine the data in the table and on the graph. What is the significance of the temperature at which the readings leveled off? If satisfied with the trial, select Store Latest Run from the Experiment menu, so a new set of data may be graphed. If not satisfied, select Clear Latest Run from the Experiment menu. 8. Save the file before proceeding to prevent accidental loss of data. If, for whatever reason, the computer were to lock up, the most recently saved set(s) of data may be retrieved. Failure to do so may result in all data being lost in an experiment. When using the computer it is always a good practice to save early and often! 9. Repeat step 4, using a fresh 100 ml sample of snow or crushed ice. Using the electronic balance, weigh out 8 g of salt. The salt may be weighed into a cup or onto a piece of paper with the sides folded up to prevent spillage. Add the salt to the snow or ice and repeat steps 5-8. Continue to gently stir without touching the sides of the cup while readings are being taken. 10. Repeat step 4, using a fresh 100 ml sample of snow or crushed ice. Add 8 g of Ice Melt, an alternative sidewalk de-icer, or baking soda (not baking powder) to the snow or ice and repeat steps 5-8. Continue to gently stir without touching the sides of the cup while readings are being taken. 11. Repeat step 4, using a fresh 100 ml sample of snow or crushed ice. Add 8 g of sugar to the snow or ice and repeat steps 5-8. Continue to gently stir without touching the sides of the cup while readings are being taken. H4.3
Name Lab Section PRELAB QUESTIONS 1. How do you predict the temperature of snow will be affected by the addition of salt? 2. Give two examples of instances where you would use computers to make a measurement. 3. Which safety precautions, if any, must be observed during this lab activity? H4.4
ASSIGNMENT 1. When finished with all of the trials: Autoscale the graph by clicking on the Scale icon on the toolbar. Title the graph by selecting Graph Options from under the Options menu and entering a title. Add a text annotation for each of the four trials by selecting Text Annotation from under the Insert menu. Drag the arrows so that each one points to a different trial on the graph. Label each of the trials by adding text to each of the text boxes. Drag the text boxes, if necessary, to make the graph look neat and organized. Save the file for a final time after these additions. 2. Write a report (2 or 3 paragraphs in length) summarizing your results. Address the following items in your report: At which temperatures did the readings level off (or become more level) in each of the four trials? Copy and paste the graph from Logger Lite into your report to support your answer. By adding the solutes, what has happened to the freezing point of each mixture? Think carefully. Were the results what you expected? Explain. Which of these substances would be the best to use on your sidewalk? Why? Think of this in terms of the freezing point of the liquid on the sidewalk. H4.5
PHOTOS - Please compress photos and save your file before uploading to the dropbox. Photos should come close to filling the boxes below and all required items should be clearly visible. Required Photo 1: Required Photo 2: H4.6
Lab Report Submission Checklist Complete the appropriate checklist and submit this page along with your lab activity. Lab Activity Submitted Via the D2L Dropbox Prelab assignment is complete. Remainder of lab activity is complete (data, questions, photos. etc.). Required photos of the procedure included. At least one photo shows face or photo I.D. At least one photo clearly shows the date. Document filename in format of Lastname Firstname HX. File size is no larger than 10 MB. Only one document submitted for this lab activity. Lab submitted on time. If late, this is your first extension. Lab Activity Submitted Via the US Postal Service or In Person Prelab assignment is complete. Remainder of lab activity is complete (data, questions, photos. etc.). Required photos (at least one showing face or photo I.D.; at least one shows the date) of the procedure or a tangible artifact or product from the lab activity is included. If return is desired, a self-addressed stamped envelope with sufficient postage is included*. Lab submitted on time (postmarked by due date if sent via USPS). If late, this is your first extension. *You may find a postage calculator at http://postcalc.usps.gov. Use the balance in your kit to find the weight. H4.7