Activity 3 Studying Carbon Dioxide GOALS In this activity you will: Generate CO 2 by various methods, then collect and characterize it. Explore how the volume of a gas varies with temperature. Compare the Celsius and Kelvin temperature scales. Safety goggles and a lab apron must be worn at all times in a chemistry lab. What Do You Think? An effervescent antacid tablet and a carbonated beverage produce a fizz that tickles your nose when you take the first mouthful. What causes you to burp after drinking a carbonated beverage? Record your ideas about this question in your log. Be prepared to discuss your responses with your small group and the class. Investigate All carbonated beverages give off gases. Under pressure, the gas can stay in the beverage. When you open the top and release the pressure, some of the gases are released but some remain in the beverage and give it the fizz. In this investigation, you will try to determine how the temperature of the drink affects the amount of gas that the liquid can hold. Part A: Collecting and Testing Carbon Dioxide Gas 1. You will first have to learn a technique for collecting a gas. The technique that you will use involves the displacement of water. First place 3 ml of water in a test tube (#1). Then place a one-hole rubber stopper fitted with a short piece of glass tubing into the mouth of the test tube. Attach rubber tubing to the glass tubing. 693
It s Alimentary Be careful with the glowing splint and other burning materials. Dispose of it carefully. Avoid breathing the gas given off by the tablet. 2. Completely fill another test tube (#2) with water and submerge it, upside down, in a container of water. Place the end of the rubber tubing from test tube #1 into test tube #2. 3. Drop one-half tablet of an effervescent antacid tablet into test tube #1. Quickly place the rubber stopper back into the mouth of the tube. 4. The water will be displaced from tube #2 by the gas coming from the effervescent antacid tablet. Keep the mouth of test tube #2 below the surface of the water. When all of the water has been displaced, place a small square of plastic wrap over the mouth of the tube. Now the test tube can be removed from the water. Put a rubber band around the mouth of the test tube to keep the plastic wrap in place. This should keep the gas from escaping. 5. Remove the plastic wrap from test tube #2 and insert a glowing splint into the tube. a) What did you observe happening? Record these observations in your log. 6. Continue to generate gas by adding more effervescent antacid tablets to test tube #1. This time, place the rubber hose into a new test tube containing 5 ml of limewater. (This time the test tube is not submerged in the water.) Observe what happens at first when the gas bubbles through the limewater. As the bubbling continues, you may have to add more effervescent antacid tablets to maintain generation of the gas. What further change do you see? limewater a) Record these observations in your log. 694
Activity 3 Studying Carbon Dioxide 7. The gas carbon dioxide CO 2 is able to extinguish a glowing splint. It reacts with limewater to form a white solid, or precipitate. The gas oxygen O 2 will ignite a splint and has no reaction with limewater. The gas hydrogen H 2 will cause a small explosion when exposed to a fire and does not react with limewater. a) On the basis of this information and your results, identify the gas produced by the effervescent antacid tablet. 8. Dispose of the materials as directed by your teacher. Part B: Temperature and Solubility of a Gas 1. Design an experiment that would help you investigate the question: How does temperature affect the solubility of the gas in carbonated beverage? (The solubility of a gas in a liquid is a measure of how much gas can remain in the liquid.) With the approval of your teacher, you may be able to move ahead with your design. Alternatively, your teacher may ask you to use the following steps, for which the equipment is available and safe. 2. Put water in a large beaker, set it on a hot plate and heat it to 37 C. Suspend a thermometer from a ringstand in the water so that the temperature can be monitored. Adjust the hot plate setting so that a temperature of 37 C can be maintained. 3. Obtain two balloons and stretch them back and forth about a dozen times. Blow into them and inflate them two or three times. This will make it easier for them to expand. Open two small cold glass bottles of a carbonated beverage and immediately place the balloons over the mouths of the bottles. 4. Submerge one bottle of the beverage in a beaker of 37 C water. Maintain the temperature of the water at 37 C. With the balloon still on the mouth of the bottle, agitate or swirl the bottle. When no more bubbles of gas are given off, use a twist-tie to tie off the balloon. Twist it tightly so none of the gas leaks out. 5. At the same time as you did in Step 4, submerge the other bottle in a beaker of ice and water. With the balloon still on the mouth of the bottle, agitate or swirl the bottle vigorously. When no more bubbles of gas are given off by the beverage, make a knot in the neck of the balloon to tie it off so that no gas can leak out. Do not use a twist-tie on this second balloon. Do not heat glass bottles directly on the hot plate. Also, do not heat the glass bottles higher than 37ºC. They can break. 695
It s Alimentary Safety goggles and a lab apron must be worn at all times in the lab. 6. Without taking measurements, roughly compare the volume of gas released from the bottle in the 37 C water with the volume of gas released from the bottle in the ice water. a) Record in your log any conclusions you can make about these volumes. What does this tell you about the relationship between temperature and the solubility of a gas in a liquid? Part C: Temperature and Volume of a Gas 1. To compare the volume of a gas at different temperatures, you need to be sure that you are comparing the volume of the same number of particles of gas. You cannot be sure that this is the case in the two balloons of gas collected above. To overcome this problem: Take the balloon of gas that you tied off. Place it in a 1000-mL beaker that contains 200 ml of ice water. There should be no pieces of ice floating in the beaker. Place a 600-mL beaker inside the first beaker so that it rests on the top of the balloon. With your hand push the 600-mL beaker down until the balloon is just submerged. In other words, the bottom of the 600-mL beaker should just be at the surface of the water but not submerged in the water. Record the volume to which the water rises in the beaker. Using the graduations on the beaker, you will have to estimate to the nearest 10 ml the total volume of the (balloon water). 2. Remove the balloon and place it in the 600-mL beaker so that it won t get mixed up with other balloons in the room. 3. Place a thermometer in the beaker containing the 200 ml of water. a) Record this starting cold temperature. 4. Heat the 200 ml of water in the 1000-mL beaker to about 80 C. Using beaker tongs or hot pads, remove the beaker from the heat source and place it on the workbench. Return the balloon to this beaker containing the 200 ml of hot water. 5. Once again, push down (with a rubber glove to limit heat on your hand) on the 600-mL beaker to entirely submerge the balloon below the surface of the water. Allow the balloon to remain submerged for a few minutes so that the gas in the balloon may come to the same temperature as the water. 696
Activity 3 Studying Carbon Dioxide 6. With your hand, move the 600-mL beaker upward until the balloon is just submerged. In other words, the bottom of the 600-mL beaker should just be at the surface of the water. a) Record the new volume to which the water has risen in the beaker. Once again, you will only be able to estimate to the nearest 10 ml the total volume of the balloon plus water. b) Remove the balloon and use the thermometer to obtain the temperature of the warm water. Record this temperature in your log. 7. Dispose of the materials as directed by your teacher. Clean up your workstation. 8. Use the data that you have recorded in your log to compute the volume of the balloon at the cold temperature. Also, compute the volume of the balloon at the hot temperature. a) Record the volumes of the balloon at the cold and hot temperatures. b) Write a statement that describes the change in volume of the gas as the temperature increased. c) By what factor did the volume of the balloon increase? d) By what factor did the temperature increase? e) Did the volume increase by the same factor that the temperature increased? Wash your hands and arms thoroughly after the activity. THE RELATIONSHIP BETWEEN TEMPERATURE AND THE VOLUME OF A GAS Testing for Carbon Dioxide In this activity, you collected carbon dioxide CO 2 gas from the effervescent antacid tablets dissolved in water. As you saw in Activity 2, gas was formed when some antacids underwent a reaction. The common chemical test for CO 2 is to bubble it through limewater (a basic, aqueous solution of calcium hydroxide). The formation of a white solid, or precipitate, confirms the presence of CO 2. The equation for this is: Chem Words limewater: a saturated aqueous solution of calcium hydroxide. precipitate: a solid that separates from a solution usually as the result of a chemical reaction of two other solutions. CO 2 (g) Ca(OH) 2 (aq) CaCO 3 (s) H 2 O(l) Upon further addition of CO 2, the white precipitate dissolves according to: CaCO 3 (s) CO 2 (g) H 2 O(l) Ca(HCO 3 ) 2 (aq) Another identifying feature of CO 2 is that it does not burn and it will not support combustion. Therefore, sticking a glowing splint into a bottle of CO 2 will cause it to go out immediately. This is the basis of using a CO 2 fire extinguisher. 697
It s Alimentary Chem Words Charles s Law: a gas law that says if the mass of a gas and the pressure of the gas are held constant, the volume of the gas will vary in a direct proportion to the temperature of the gas. direct proportion: a mathematical relationship that says, as one quantity increases the other one will increase so that their ratio remains constant, or if one quantity decreases the other one will decrease so that their ratio remains constant. Solubility and Volume of Gas and Temperature As the name indicates, carbonated beverages (drinks) contain CO 2 that has been dissolved in the liquid under pressure. Opening the can or the bottle allows the gas to be released and the pressure to be reduced. You found in the activity that as the temperature increased, more gas was released from the liquid. The solubility of the gas in the liquid decreased as the temperature increased. If the beverage is cold when it enters the stomach, it gets warmed up because the temperature of the stomach is around 37ºC, about 30º warmer than the cold, carbonated drink. More CO 2 will be released in the stomach than if the carbonated beverage remained at room temperature. This is because CO 2 is less soluble in warm liquids than in colder liquids. All that gas in your stomach causes you to burp. You also found that increasing the temperature of the gas increased the volume of the gas. Charles s Law This relationship between temperature and volume is called Charles s Law. Jacques Charles was an avid hot-air balloonist back in the 1800s. Because he was concerned about the volume his balloon must maintain, he very carefully measured the relationship between the temperature and volume of the gas in his balloon. With the help of another Frenchman, Joseph Louis Gay-Lussac, the law known today as Charles s Law was formulated. It says that there is a direct proportion between temperature and volume if a constant mass of gas remains at constant pressure. This means that if the temperature goes up, the volume will go up proportionally. And, if the temperature goes down, the volume will also go down proportionally. Note that this relationship is only valid if the pressure and the mass of the gas remain constant while the volume and temperature change. 698
Activity 3 Studying Carbon Dioxide Examine the following data that scientists from the 1800s might have collected: A 1.00 L volume of gas with an initial temperature of 15ºC was warmed to 30ºC. The volume increases to 1.05 L. Just as you found, increasing the temperature also increases the volume. By using Kelvin as the temperature scale, the result is more profound. The Kelvin scale has the same increments as the Celsius scale, but 0 K is equal to 273ºC and this temperature is known as absolute zero and is thought to be the coldest temperature possible. (The Kelvin scale does not use the degree symbol.) You can see the relationship between Celsius and Kelvin on the thermometer pictured. The Kelvin temperature is found by adding 273 to the Celsius temperature. As a conversion equation, you can write that K 273 ºC. Returning to the sample data, you now see that the temperature increase in kelvins was from an initial temperature of 15ºC, or 288 K to a final temperature of 30ºC or 303 K. The Kelvin temperature ratio is 303/288 1.05 times as big. This is identical to the volume change. This is an enormous breakthrough in thinking about gases. This means that the absolute temperature and volume really are directly proportional. As the absolute temperature went up by a factor of 1.05, the volume also went up by a factor of 1.05. In the equation for Charles s Law, the amount and pressure are constant: V 1 T1 V 2 T2 and V is the volume and T is absolute temperature (ºC 273.15 K) If you want to double the volume of a gas, you must also double the temperature of the gas (using the Kelvin scale). In your initial example of 1.0 L of gas at 15ºC, or 288 K, you would have to double the temperature to 2 288 K 576 K to double the volume to 2.0 L. (576 K is equal to 303ºC.) Doubling the Kelvin temperature in this case increases the Celsius temperature by a factor of 20. Celsius temperature 30 303 15-273 288 0 absolute zero Chem Words kelvins: the base unit of temperature. One kelvin represents the same temperature difference as one degree Celsius. absolute temperature scale: a temperature scale where absolute zero is taken as 0 K and on which there are 100 divisions between the freezing point of water (273.15 K) and the boiling point of water (373.15 K). Kelvin temperature 699
It s Alimentary Checking Up 1. What is a chemical test for the presence of CO 2? 2. What does Charles s Law say? 3. Define the term directly proportional. 4. Which temperature scale must be used when solving problems using Charles s Law? 5. What are two properties of CO 2 that make it useful in a fire extinguisher? There are other gas laws that you will be learning about and they will all be simpler to understand when you use absolute Kelvin temperatures instead of Celsius temperatures. Increasing Temperature at the Molecular Level You have investigated some of the macroscopic properties of gases. As student chemists, you are also interested in what is happening at the molecular level. The molecules of CO 2 gas are in constant motion. The temperature is a measure of the average kinetic energy of these molecules. The higher the temperature, the faster the molecules move and the greater the kinetic energy associated with this motion. When the temperature increases, you expect that the faster-moving higher energy molecules will be able to push on the balloon more than slowermoving molecules. This is why the volume of the balloon begins to increase. As the volume gets larger, fewer particles hit the wall every second. The enlarged balloon stops expanding when the increase of the energy of the molecules is exactly balanced by the decrease in the number of particles hitting the balloon per second. What Do You Think Now? At the beginning of this activity you were asked: What causes you to burp after drinking a carbonated beverage? Now that you have completed this activity, how would you answer the question? What does it mean? Chemistry explains a macroscopic phenomenon (what you observe) with a description of what happens at the nanoscopic level (atoms and molecules) using symbolic structures as a way to communicate. Complete the chart below in your log. MACRO NANO SYMBOLIC What happens to the size of a balloon filled with gas as you heat it? On the molecular level, explain how increasing the temperature of the gas will increase the volume. Draw a sketch that depicts the different behavior of gas molecules at 288 K and then at 576 K. 700
Activity Activity 3 Studying # 38 RunningH Carbon Dioxide Activity How do you know? Use your data to explain Charles s Law: Why do you believe? V 1 T1 V 2 T2 To celebrate a friend s birthday, you purchase a mylar balloon (a shiny balloon material). It s very cold outside and when you leave the store, you see that your balloon is no longer inflated. You go back into the store to complain about the leak in the balloon. But as you explain the problem, the balloon inflates again. Explain what is occurring. Why should you care? If your ride were to have the riders navigate the potential problem of being burped out of the body, how would you describe this? Reflecting on the Activity and the Challenge Recall that in this activity you investigated the properties of carbon dioxide and various ways that carbon dioxide can be produced. Certain medicines, foods, and beverages may produce carbon dioxide in a chemical reaction. Carbonated beverages contain carbon dioxide gas that can escape from the liquid. If you drink a cold soft drink, the volume of carbon dioxide gas will expand as it warms in your stomach. This knowledge of chemistry can be applied to the skit needed for your part of the ride through the alimentary canal. Imagine what you would experience when you are in the stomach, clinging to a particle of food, and the carbonated beverage that has just entered the stomach starts warming up. Molecules of CO 2 as big as you are being released and are moving toward you at a high speed. More and more of them keep coming! The ride might get a little rocky for a while. 1. Charles s Law in chemistry states that the temperature and the volume of a gas are directly proportional if the pressure and amount remain constant. a) Write this as an equation. b) Draw a graph that represents a direct proportion between the variables of volume (y-axis) and temperature (x-axis). 2. To test for the presence of CO 2 you bubbled the gas through limewater. a) What is limewater? 701
It s Alimentary b) Write the balanced chemical equation for the chemical reaction that occurs when carbon dioxide is bubbled into limewater. c) What is the chemical name of the white solid product (precipitate) formed in the test for carbon dioxide? 3. Which is the higher temperature, 27 C or 270 K? By what factor is one bigger than the other? 4. Explain why Kelvin temperatures are always positive. 5. The average human body temperature is 98.6 F, which is 37.0 C. a) What is this temperature on the Kelvin scale? b) What is done mathematically to change a Celsius temperature to a Kelvin temperature? 6. Convert 150 K to its Celsius equivalent. 7. If the volume of a gas in a flexible container is 444 L at a temperature of 200 K, what will the volume be if the temperature falls to 100 K, assuming that the pressure remains constant? 8. The temperature outside the city bank reads 278 K (the bank president is a former chemistry teacher). a) What would be the appropriate clothes for the day, a bathing suit, or a heavy jacket? b) Because some of the people in the bank do not understand the Kelvin scale, the other side of the flashing temperature sign gives the temperature in C. If the one side flashes 310 K, what does the other side flash in C? 9. Preparing for the Chapter Challenge You can certainly use the concept of the effect of temperature of a gas on its solubility and on its volume. Determine a way in which your ride will use these relationships. Write an explanation of the chemistry principles and how you know about them as part of your challenge. Inquiring Further 1. Who were Fahrenheit, Celsius, and Kelvin? Compare the scientific work of Gabriel Fahrenheit, Anders Celsius, and Lord Kelvin. What did they have in common? 2. Dry Ice What is dry ice? At what temperature is dry ice stored? What are some uses of dry ice? 702