Bill Wagenborg Chemistry Lesson Plan March 2007 Lesson Title: Understanding Charles Law Grade Level: 8 Time Frame: 1-2 (45 Minute) Classes Goals/Objectives: The Students Will Be Able To: - follow a sequenced plan of instructions - describe changes to gases caused by the addition and absence of heat(rise and fall in temperature) - use process skills to make inferences and predictions using collected information - explain the concepts involved in Charles Law through discussion and written words Pennsylvania Standards: 3.1.10 E: Describe patterns in nature, physical and man made systems. 3.2.10 B: Apply process knowledge and organize scientific and technological phenomena in varied ways. Opening (Attention Grabber) Materials: Empty Soda Can, Hot Plate, 1 Liter Beaker, Tongs, Tap Water Teacher Action: 1.Fill up the beaker with room temperature water. 2.Place just enough water in the soda can to cover the bottom. 3.Turn the hot plate on, place the soda can on top and heat the can until the water begins to boil. (You should see steam flowing from the top of the can) 4.Using the tongs, grab the can at the bottom and quickly place the top portion of it in the beaker upside down. (The sides of the can will crush inward) 5. Allow students to hypothesize why this occurred and explain that today they will be doing a lab that may help them understand what happened. ***Caution: Before doing this demonstration inspect the beaker for any cracks and make sure the students are not extremely close. The force of the can crushing in a beaker with a tiny crack can cause the beaker to break. (This happened to me before when I was testing it before class. I reinforce the top of beaker I use with duct tape before doing this demonstration in order to prevent any accidents) 1
Materials For Lesson: For Each Group: 2 balloons (be mindful of student allergies when choosing the type) 2 250 ml beakers 2 thermometers 2 aluminum pie pans (6-12 inches) For The Class: Crushed ice Tap water Hot Plate(s) Pre-Class Questions: What do you think will happen to a balloon if you heat it? Why? What if you cool it? Why? Draw a picture of what the gas might look like inside the balloon for each instance. Lesson: Part A The students are broken up into groups and each group will blow up a balloon in a 250 ml beaker. The balloon should fit firmly against the insides of the beaker. They will then place the beaker in an aluminum pie shaped container. This container will be a water bath filled with room temperature water. Using a thermometer, the students will take and record the temperature of the water and observe the balloon. They will make a drawing of what they think the gas looks like inside the balloon. The students will then place the container with the beaker in it, on a hot plate and heat the water. (We do not have any Bunsen burners or access to gas for that matter). They will take the temperature of the water at equal intervals (every 30 seconds for 5 minutes) and observe what happens to the balloon in the beaker until the water begins to boil. The students will be recording all of the information and observations in their lab journals. They also will draw a picture of what they think the gas inside the balloon looks like after the five minutes of heating. They will compare this to their drawing of the gas before they added heat to the balloon and the prediction they made in their pre-class drawing of a heated balloon. Part B The students will blow up another balloon inside a second 250 ml beaker and again place it in a room temperature water bath in an aluminum pie plate. They will record the temperature and observe the balloon s size in the beaker. They will make a drawing of what they think the gas looks like inside the balloon. 2
Assessments: The students will then begin to fill the water bath with crushed ice. They will record the temperature, observe the balloon and add more ice. All will be done over equal time intervals (30 seconds for 5 minutes). As they did in part a, they will record all information in their lab journals. They also will draw a picture of what they think the gas inside the balloon looks like after the five minutes of cooling. They will compare this to the drawing they made of the gas before they added the ice and to their pre-class drawing of a cooled balloon. After the lab (that day if time permits or the following class), we will have a discussion about what the students observed and what they think may have caused their results. They will also record their thoughts and experiences with this lab in their lab journals. I will serve as a moderator/guide and not an answer person. I want to see what their thoughts are and that they arrived at their conclusions on their own. 1. The students will be given follow up questions dealing with their lab that will be used as an assessment. The questions will be phrased in a way where I will be able to see if they understand why the balloon increased in size in the hot water and decreased in size for the cold. I want to make sure that they realize that the volume of the gas inside the balloon is increasing and decreasing. For example: Were your predictions from the pre-class correct? Explain Based on your observations, what happens to a balloon when heated and when cooled? What affect does the temperature have that causes the balloon to act this way? Using this lab and what we learned about Boyle s Law in our previous unit as a basis, explain why the soda can got crushed in our opening activity?(if Boyle s Law is taught after Charles Law you can just focus on their explanations from the temperature and volume viewpoint now, and readdress the pressure at a later point) 2. They will also be given a question on their unit test that takes Charles Law and puts in a real world context. For example: Why do the tires on your car appear to be deflated in the morning after a cold night? How does this show Charles Law? Or 3
You are a manager of a party store. It is a cold day and a person just buys a bunch of balloons before leaving the store. She returns minutes later complaining that her balloons are deflated. Using what you have learned about Charles Law, give your response to the customer. Story of Charles Law (See Page 7): During the following class or lab wrap up session, the students will hear the story of how Charles Law came about and how it relates to balloons. It provides the students with a connection between a science law and a real world application. 4
Story of Charles Law To begin the story of Charles law, we should first look at the early attempts of discovery by Robert Boyle and Guilliame Amonton. In 1622 Boyle had published his work on the inverse relationship between a gas pressure and volume, a law that would later bear his name. He was aware of the increase in volume of a gas when heated, but a temperature scale did not exist then. In the early 1700 s Amonton did many experiments involving a gas volume and its temperature, but like Boyle a temperature scale did not exist. (Thall, n.d.) So we can now look at the gentleman who the law is named after. Jacques Charles was a Frenchman who early on in his life had very little science education. While working in a Paris Government Office he had a chance encounter with the American Ambassador to France, Benjamin Franklin. After hearing of Franklin s experiments and scientific ideas, Charles decided to teach himself some science. This self teaching eventually led to public lectures and then to the Academy of Science, where he began to develop a respectable reputation. (Ellyard, 2005) It was here in 1783 that the Montgofier brothers asked Jacques to look at their new mode of travel, the hot air balloon. After careful scrutiny, Charles stated that he believed that for the safest and surest form of travel the balloon should be filled with a very light flammable air (hydrogen) rather than heating the air over fire. (Ellyard, 2005) In August of that year he but his theories to the test. He got his first balloon and filled it with hydrogen by pouring sulfuric acid over scrap iron (later zinc). He went to a field, where the Eiffel tower now stands, and sent his balloon up 10 km. After more trials he soon started to notice that the balloon s volume would expand as the balloon went up into lower air pressure. This was not anything new; it was simply proving Boyle s Law from 1659. More importantly he saw a connection between heating the gas and the gas volume. (Ellyard, 2005) In 1787 Charles decided to investigate this relationship further. He went out and got a J-shaped glass tube that Robert Boyle had used in his study of gases. He placed the tube in a water bath so he could manipulate the temperature of the gas. He held the pressure of the trapped gas bubble steady by keeping a constant difference between mercury levels in the two arms of the tube, (Ellyard, 2005) This would make pressure a non factor in his experiments. He then went about changes the temperature of the water bath and observing the effect on the trapped gas bubble. His results showed that 5
the volume of the gas rose with an increase in temperature and fell with a decrease in temperature, (Ellyard, 2005) This relationship was dubbed Charles Law. This may not be fair for two reasons. First Charles was not the first to discover this relationship. Gulilliame Amontons had done so in 1702, but Charles apparatus was better and he had more precise measurements. Secondly Charles never published his work on the relationship between a gas volume and its temperature. That distinction would go to Gay Lussac. (Ellyard, 2005) After the French Revolution, fourteen year old Joseph Gay-Lussac went to Paris. It was here that he received private lessons and attended boarding school. He eventually became an assistant to French chemist Claude Louis Berthollet who trained him in chemical research. During the winter of 1801-1802, twenty-four year old Gay-Lussac was encouraged by Berthollet to conduct research on the expansion properties of gases. (Green, Peterson, 1992) Gay-Lussac wanted to get results that were more accurate than those obtained by Charles and others. In his experiments he excluded water vapors from his apparatus and made sure that the gases themselves were free of moisture. He concluded that equal volumes of gases expand equally with the same increase in temperature. (Lussac, 1802) There were some differences between his results and Jacques Charles. First of all, Gay-Lussac published his results while Charles did not. Gay- Lussac also measured the coefficient of expansion while Charles did not. Charles only investigated oxygen, carbon dioxide, nitrogen and air.gay- Lussac s results worked for all gases. Finally, because Charles had water in his apparatus, his results showed an unequal expansion for the gases that were water soluble. Gay-Lussac had obtained more accurate results and published them yet the law is still more commonly referred to as Charles Law than Gay-Lussac s Law. (Green, Peterson, 1992) Like Charles before him, Gay-Lussac was an avid balloonist. In 1804 he flew to an altitude of 23,000 feet which was a record that stood for half of a century. Eventually as, Charles predicted, hot air balloons were replaced by hydrogen filled and later helium filled balloons. In the 1960 s hot air ballooning became popular again as a sport. (Reese, 2004) Charles and Gay-Lussac s results helped other scientists discover the absolute zero temperature of a gas. This is done by locating the theoretical temperature in which gas has a volume of zero. (Ellyard, 2005) This is the coldest temperature possible. It has never been achieved because gas liquefies before reaching this temperature and is no longer subject to the gas laws. (McGrath, 2005) 6
References Ellyard, David (2005) Who Discovered What When. Sydney: Reed New Holland. Gay-Lussac, Joseph (1802) Annales de Chimie 43, 137 (1802) [reprinted in William Francis Magie, ed., A Source Book in Physics (New York: McGraw-Hill, 1935)]. First Section. Retrieved February 19,2007 from http://web.lemoyne.edu/~giunta/gaygas.html Green. Jeffery M., Peterson, Andy (1992) Gay-Lussac-Scientist. Retrieved February 19,2007 from http://www.woodrow.org/teachers/ci/1992/gay-lussac.html McGrath, Kimberly (ed.) (2005) World of Physics. Farmington, Michigan: Thomas Gale Publishing. Retrieved February 19, 2007 from http://www.bookrags.com/research/charles-law-wop/ Reese, K.M. (2004) Gay-Lussac, Balloon Pioneer. Chemical Engineering News. Volume 82(25) Pg 56 Thall, Edwin (n.d) Thall s History of Gas Laws. Retrieved February 19,2007 from http://mooni.fccj.org/~ethall/gaslaw/gaslaw.htm *Soda can demonstration and balloon lab based on those found in The School District of Philadelphia s 8 th Grade Science Textbook. Holt Science and Technology: Introduction to Matter (2005) Holt, Reinhart and Winston: Austin Texas. * All photos are the property of William J. Wagenborg Jr. and may not be used by anyone in any way. 7
Pictures To Be Used For Lesson Jacques Charles (http://dbhs.wvusd.k12.ca.us/webdocs/gaslaw/gas-charles.html Joseph Gay-Lussac (http://dbhs.wvusd.k12.ca.us/webdocs/gallery/gallery6.html) http://discover.edventures.com 8
More Links These are links to some Charles Law graphics. http://www.1728.com/charles.htm http://exploration.grc.nasa.gov/education/rocket/glussac.html http://www.chem.iastate.edu/group/greenbowe/sections/projectfolder/flashfiles/gaslaw/c harles_law.html These are links to more information on hot air ballooning. http://www.planoballoonfest.org/balloon_history.html http://www.nationalballoonmuseum.com/exhibits.cfm?exhibitid=18 9