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 Gases LabThe reference material at the start of this lab was written by Ian Guch () and the lab itself was written by Patricia Warner at Northwest Missouri State University ().Let Loose the Gases! Gases are really, really important. The tire in your car wouldn’t stay inflated unless it was full of gas. The balloons at your birthday party wouldn’t stay inflated if it weren’t for the helium they put in them. The ping pong balls you use to keep you entertained are full of air, which probably has something to do with their bounciness, though I’m not really sure. Gases are all over the place!Boyle’s Law Boyle’s law says that when you squish a gas, its pressure goes up. Usually expressed as P1V1 = P2V2, Boyle’s law just says that the pressure and volume of a gas are inversely proportional to each other (i.e. as one goes up, the other goes down).Charles’s Law Charles’s law states that when you increase the temperature of a gas , it gets bigger. This is usually attributed to the fact that the particles in a hot gas fly around at higher speed, causing them to hit the side of their container harder and push it outward. If you want to see the math version of this equation, check this out:Gay-Lussac’s Law Gay-Lussac said that if you increase the temperature of a gas that’s stuck in a sealed container, the pressure of the gas will increase. The idea here is that if you increase the speed at which the particles travel, they’ll hit the side of the container at a higher speed, causing the pressure inside to go up. For those of you who like equations, Gay-Lussac’s law is numerically expressed as:The LabSimulation url: (This simulation requires Java.)This lab will be mainly inquiry. Translated, that means that there are no step-by-step instructions. You will need to figure out how to conduct the investigation on your own. 1. In the chart below, explain in words what you think a graph of each of the following will look like: (Will it be a straight line? Will it be a curved line? Will the line slope up or down?)Variables AnalyzedPrediction of what graph will look likeVolume vs PressureVolume vs TemperatureTemperature vs PressureNumber of Particles vs Volume2. Now, test your predictions. Remember, when experimenting, all other variables except the one you are testing must remain the same. The variable you are testing is called your independent variable. What happens based on your change in independent variable is what you are measuring (dependent variable). Later, you will be graphing these in Excel. Your independent variable will go on the x-axis and your dependent variable will go on the y-axis. [HINT: When you put your numbers in Excel, the independent variable should be placed in the first column and the dependent in the second. This will force Excel to place your variables on the correct axes.]FOR EXAMPLE: On the first scenario, I want to change the volume and see what happens to the pressure. First, make sure ‘Temperature’ is checked at the top right because we want it to remain the same. Pull the little man as far as you can to the left. Click the measurement tools button (on the right) and check the ‘ruler’ box. Align the ruler so you can measure the box:Since we measure volume by taking length x width x height, we will use the length of the box as our volume number (since the width and height do not change). If you do not have any gas molecules in the box, pump the handle five times to put some in. Record the initial volume (length). In this case, 8.2 nm. What does the pressure gauge read? Record that value. You will need to make a data table to record this information. Feel free to jot one down on scratch paper or just place it in Excel. Now push the little man in 1.0 nm. Let the pressure adjust and record the new length and the new pressure on your data table. Continue until you have at least five measurements.Conduct the same type of investigations for: volume-temperature, temperature-pressure, and number of particles-volume. Make graphs in Excel for each of your four investigations. Include them on a separate sheet of paper.For full points, graphs must have a proper title, have both axes labelled (including units), and have a trendline. Sometimes ‘best fit’ lines are not linear. In that case, to get the ‘best fit’ line, experiment with the different trendline options on the pop-up menu on the right. Use the trendline that best fits your data points.3. After graphing, complete this table:RelationshipDirect or inverse?Constant parameters?Whose law?V vs PV vs TT vs PMoles vs VN/AANALYSISAnswer the following based on information you gathered in the simulation or by performing more simulations.1. Why do bicycles tires seem more flat in the winter than in the summer?2. Why is it possible that a can of soda pop can explode if left in the hot sun?3. A rigid container filled with a gas is placed in ice. What will happen to the pressure of the gas? What do you think will happen to the volume?4. An infected tooth forms an abscess (area of infected tissue) that fills with gas. The abscess puts pressure on the nerve of the tooth, causing a toothache. While waiting to see the dentist, the person with the toothache tried to relieve the pain by treating the infected area with moist heat. Will this treatment help? Why or why not?Instructor notes for this lab:The basic material for this lab should be fairly straightforward. Students should be familiar with the three PVT gas laws and should know how to use them. If desired, you may want to teach your students the combined gas law and just explain that it can be used for any PVT gas law problems by leaving out any variables that aren’t mentioned in the question:P1V1T1= P2V2T2 Where the “1” refers to initial conditions of each variable and the “2” refers to the final conditions of each variable after a change has been made.The lab itself should be fairly straightforward. The requirements are as follows:One computer for each lab group (preferably each individual) that can run Java.A networked printer that each of the computers can use for printing.A spreadsheet program. Though Microsoft Excel is mentioned here, free spreadsheet programs that you can use include LibreOffice () and Google Sheets ().There are some potential difficulties that arise in this lab, but nothing that should be too difficult to work around. These include:IT problems. For some reason, computer systems that work perfectly will act up once you have a group of people who actually need to use them. If the printer goes down, you can always have students email you their graphs. If the computers go down, some students will have phones or computers of their own that they can use.Problems understanding how to use the program. This will happen in any simulation, and sticking to the idea that they have to figure it out via inquiry is the best way to go. It’s amazing how a “helpless” student can figure things out on their own!Answers to the questions:Within the lab:Question 1: They’ll make predictions. As long as it’s clear what they’re talking about, it’s fine.Question 3: These should be pretty straightforward for the students to figure out. The answers:RelationshipDirect or indirect?Constant parameters?Whose law?V vs. PInverseTBoyle’sV vs. TDirectPCharles’sT vs. PDirectVGay-Lussac’sMoles vs. VDirectP, TN/AAnalysis questions:1.There are several ways to look at this:As temperature decreases, the pressure will decrease. This lack of pressure allows the weight of the bicycle itself to squish the wheel more and make it look flat.As temperature decreases, the volume will decrease. This assumes that you have a container with a constant pressure applied on it (like a piston), but given that the atmospheric pressure is (roughly) the same in summer and winter and the weight of the bike is also the same, this should pretty well approximate a piston. One way NOT to look at this (though it’s creative): Bikes are usually ridden less in the winter than in the summer, so they haven’t been pumped up as recently. They don’t just look flatter - they are flatter. While creative, it misses the point.2. There are two things involved here. Let’s make the assumption that soda consists of carbon dioxide dissolved in water.When the temperature of aqueous solutions increase, gases become less soluble in water. Because it’s less soluble, more of it will be in the gas form. This will increase the pressure inside the can.As the temperature of this gas increases, Gay-Lussac’s law tells us that its pressure will also increase due to thermal expansion.When the increased amount of gas in the can is combined with the increased pressure of a hot gas, the can will eventually burst!3. The pressure of the gas will decrease, according to Gay-Lussac’s law, which states that, in a rigid container, lower temperatures will lead to lower pressures. The volume of the container will remain unchanged, assuming that it’s rigid enough to withstand the partial vacuum within.4. This will not help and will probably make things slightly worse. When a gas in a sealed container is heated, its pressure will increase. Given that the temperature of hot water from the tap is usually around 328 K and that infected human tissue usually has a temperature around 314 K, we would expect the pressure inside of the tooth to increase by 5.85 kPa. While this is only about 5% of normal atmospheric pressure, it certainly wouldn’t feel good against an inflamed tooth. Interestingly, putting ice on the tooth would also be a bad idea - decreasing the temperature of your 314 K tooth to 273 K would result in a decrease in pressure of 13.3 kPa, which is around 13% less than atmospheric pressure. As a partial vacuum probably wouldn’t make an exposed nerve feel any better, it’s probably best not to do this either. Dry having some aspirin and crying pitifully until the nurse lets you in to see the dentist. ................
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