SCIENCE EXPERIMENTS ON FILE Revised Edition 5.53-1 Disappearing Liquids and Collapsing Cans David C. Tucker Topic Evaporation and vapor pressure Time 2 days between observations; 1 hour for procedures! Safety Please click on the safety icon to view the safety precautions. Adult supervision is required. Wear safety goggles. Do not use open flame, and keep flammable liquids away from the heat source. Avoid inhaling fingernail polish remover. Work in a well-ventilated room. When leaving liquids overnight to evaporate, be sure they are near an open window or in a garage or shed away from enclosed living quarters. Wash your hands thoroughly after procedures. Materials four identical glasses (do not use plastic) metric measuring cup or 200-mL beaker glass jar with top 500 ml each: cooking oil, fingernail polish remover, rubbing alcohol 1 L water grease pencil tablespoon metric ruler hot pad or oven mitt tongs four empty aluminum soda cans straight-sided 9-in. pie pan, other similar pan, or glass tray heat source: hot plate or electric stove paper towels Procedure PART A: EVAPORATION 1. With the grease pencil, number the glasses or beakers 1 to 4. 2. Measure out 100 ml water, and pour it carefully into glass 1. Dry the measuring cup or beaker with paper towels. Fill the jar about halfway with water, cover it, and set it aside. 3. Measure out 100 ml rubbing alcohol, and pour it into glass 2. Thoroughly rinse and dry the measuring cup or beaker. 4. Measure out 100 ml nail polish remover, and transfer it to glass 3. Rinse and dry the measuring cup again, and then measure out 100 ml cooking oil and pour it into glass 4. 5. With the grease pencil, mark the level of liquid in each glass and in the jar of water.
5.53-2 SCIENCE EXPERIMENTS ON FILE Revised Edition 6. Using the ruler, measure the height of the liquid in each glass, and record this on data table 1. Measure from the inside (top) of the base of the glass to the top of the liquid, so that you do not include the thickness of the base of the glass in your measurement. DATA TABLE 1 Glass no., liquid Initial Height at Height at height (mm) 24 hr (mm) 48 hr (mm) 1. Water 2. Alcohol 3. Nail polish remover 4. Oil 7. Set the four glasses aside in a well-ventilated place by an open window or in a garage or shed away from normal living and working areas. Be sure that there are no fire hazards near the flammable liquids and that the glasses are in a secure place where they will not be knocked over. 8. After 24 hr, measure the heights of the liquids again, and record them on data table 1. 9. Measure the heights again at 48 hr, and record them. Observe the covered jar of water. Record any change in water level and anything else you notice about the inside of the jar. Are there any changes on the upper inside surface of the jar? PART B: VAPOR PRESSURE You have observed in Part A that some liquids evaporate more quickly than others. Just as liquids have different rates of evaporation, they also have different vapor pressures. You will now test the vapor pressures of the liquids whose evaporation rates you have observed. You can do this by boiling a bit of water in a can and then closing the opening of the can while cooling the steam inside. Then some of the water vapor will condense, suddenly reducing the pressure inside the can, tending to make it collapse under the higher air pressure outside. Close the opening of the steam-filled can by submerging the can upside down in a pan of one of the four liquids being tested. If the vapor pressure of a liquid is relatively low, the can will collapse. But if the vapor pressure of a liquid is high enough, vapor from the liquid will quickly increase the pressure in the can and prevent its collapse. Before doing this procedure look back over your observations from Part A. Consider whether or not how fast a liquid evaporates might affect its vapor pressure, and make a guess about which of the liquids you are testing will cause the can to collapse. 1. Fill the pan with water to a depth of 3 cm. 2. Put about 1 tbs water into one of the empty cans. Place the can on the hot plate or electric stove, and heat until the water boils. Watch for steam to come out of the opening in a stream. 3. Using the oven mitt and the tongs, grasp the can and quickly turn it upside down in the pan. Record on data table 2 what happens. 4. Repeat steps 2 and 3, using the different liquids in the tray. Always boil just 1 tbs water in the can. The other liquids are only used in the tray. Record your results on data table 2.
SCIENCE EXPERIMENTS ON FILE Revised Edition 5.53-3 DATA TABLE 2 Can Liquid used in tray Results 1 2 3 4 5. Which liquid has the fastest evaporation rate? Which has the slowest? 6. What happened to the can you immersed in the liquid that had the slowest evaporation rate? 7. What happened to the can you immersed in the liquid with the fastest evaporation rate? 8. What happened to the cans immersed in the other two liquids? 9. Do your results show a relationship between a liquid s evaporation rate and its vapor pressure? Do liquids that evaporate quickly have a higher or lower vapor pressure than ones that evaporate more slowly? Explain why you think so. 10. Explain what happens to the pressure in the can full of steam when you turn it upside down over the pan full of water or oil. 11. What happens when you use the other liquids in the pan? What s Going On The fingernail polish remover has the fastest evaporation rate. The cooking oil has the slowest. The can inverted in the oil collapses. The can inverted in the fingernail polish remover does not collapse. The can inverted in water collapses; the one over alcohol does not. There is a relationship between vapor pressure and evaporation rate. The cans inverted over liquids with fast evaporation rates did not collapse, indicating that these liquids have high vapor pressures. The cans inverted over liquids that evaporate slowly did collapse because these liquids have low vapor pressures. When the can full of steam is inverted in water or oil, the steam inside condenses, and the pressure inside the can goes down, so it collapses under the greater air pressure outside. The fingernail polish remover and alcohol have higher vapor pressures, corresponding to their fast evaporation rates. Their vapors immediately rush into the can, equalizing pressure so that the can does not collapse. Connections If you have ever left a glass of water out for a few days, you ve probably noticed that some of the water disappears. When liquids are exposed to air, some of their molecules escape into the air in the form of vapor. This is called evaporation. If liquid is in an enclosed container with air inside, it will also evaporate. When the vapor from the liquid mixes with the enclosed air, the pressure inside the container increases. When the enclosed air has absorbed as much vapor from a liquid as it can, it is said to be saturated. Any further evaporation will condense back out of the air in liquid form again. You may have seen evidence of this condensation inside bottles in your refrigerator. The amount of pressure added to the saturated air by the evaporating liquid is called the liquid s vapor pressure. In this experiment, you compared the evaporation rates of four different liquids and observed an effect of vapor pressure.
Safety Precautions READ AND COPY BEFORE STARTING ANY EXPERIMENT Experimental science can be dangerous. Events can happen very quickly while you are performing an experiment. Things can spill, break, even catch fire. Basic safety procedures help prevent serious accidents. Be sure to follow additional safety precautions and adult supervision requirements for each experiment. If you are working in a lab or in the field, do not work alone. This book assumes that you will read the safety precautions that follow, as well as those at the start of each experiment you perform, and that you will remember them. These precautions will not always be repeated in the instructions for the procedures. It is up to you to use good judgment and pay attention when performing potentially dangerous procedures. Just because the book does not always say be careful with hot liquids or don t cut yourself with the knife does not mean that you should be careless when simmering water or stripping an electrical wire. It does mean that when you see a special note to be careful, it is extremely important that you pay attention to it. If you ever have a question about whether a procedure or material is dangerous, stop to find out for sure that it is safe before continuing the experiment. To avoid accidents, always pay close attention to your work, take your time, and practice the general safety procedures listed below. PREPARE Clear all surfaces before beginning work. Read through the whole experiment before you start. Identify hazardous procedures and anticipate dangers. PROTECT YOURSELF Follow all directions step by step; do only one procedure at a time. Locate exits, fire blanket and extinguisher, master gas and electricity shut-offs, eyewash, and first-aid kit. Make sure that there is adequate ventilation. Do not horseplay. Wear an apron and goggles. Do not wear contact lenses, open shoes, and loose clothing; do not wear your hair loose. Keep floor and work space neat, clean, and dry. Clean up spills immediately. Never eat, drink, or smoke in the laboratory or near the work space. Do not taste any substances tested unless expressly permitted to do so by a science teacher in charge. USE EQUIPMENT WITH CARE Set up apparatus far from the edge of the desk. Use knives and other sharp or pointed instruments with caution; always cut away from yourself and others. Pull plugs, not cords, when inserting and removing electrical plugs. Don t use your mouth to pipette; use a suction bulb. Clean glassware before and after use. Check glassware for scratches, cracks, and sharp edges. Clean up broken glassware immediately. v
vi Safety SCIENCE EXPERIMENTS ON FILE REVISED EDITION Do not use reflected sunlight to illuminate your microscope. Do not touch metal conductors. Use only low-voltage and low-current materials. Be careful when using stepstools, chairs, and ladders. USING CHEMICALS Never taste or inhale chemicals. Label all bottles and apparatus containing chemicals. Read all labels carefully. Avoid chemical contact with skin and eyes (wear goggles, apron, and gloves). Do not touch chemical solutions. Wash hands before and after using solutions. Wipe up spills thoroughly. HEATING INSTRUCTIONS Use goggles, apron, and gloves when boiling liquids. Keep your face away from test tubes and beakers. Never leave heating apparatus unattended. Use safety tongs and heat-resistant mittens. Turn off hot plates, bunsen burners, and gas when you are done. Keep flammable substances away from heat. Have a fire extinguisher on hand. WORKING WITH MICROORGANISMS Assume that all microorganisms are infectious; handle them with care. Sterilize all equipment being used to handle microorganisms. GOING ON FIELD TRIPS Do not go on a field trip by yourself. Tell a responsible adult where you are going, and maintain that route. Know the area and its potential hazards, such as poisonous plants, deep water, and rapids. Dress for terrain and weather conditions (prepare for exposure to sun as well as to cold). Bring along a first-aid kit. Do not drink water or eat plants found in the wild. Use the buddy system; do not experiment outdoors alone. FINISHING UP Thoroughly clean your work area and glassware. Be careful not to return chemicals or contaminated reagents to the wrong containers. Don t dispose of materials in the sink unless instructed to do so. Wash your hands thoroughly. Clean up all residue, and containerize it for proper disposal. Dispose of all chemicals according to local, state, and federal laws. BE SAFETY-CONSCIOUS AT ALL TIMES