Exploring the Chemical World, PGCC, 2003 105 NAME_______________________ SECTION________________ PARTNERS _________________ DATE___________________ THE BEHAVIOR OF GASES This activity explores the interactions of gas pressure, temperature, volume, and amount of gas by looking at the behavior of gases under changing conditions. PRE-LAB QUERIES 1. Each of the flasks below has a volume of 2 liters. Draw what 1 liter of air, 1 liter of water, and 1 liter brick would look like if they were in the flasks. This is the macroscopic view (the way we see it). 1 liter air 1 liter water 1 liter brick In the next set of 2 liter flasks imagine that you could see the particles (atoms or molecules) in air, water, and brick, and use little circles to draw what they would look like in the jar. This is the microscopic view or the view at the molecular or atomic level. 1 liter air 1 liter water 1 liter brick 2. What is a major difference between the gas state and the solid or liquid state?Exploring the Chemical World, PGCC, 2003 106 PROCEDURE 1. If you take a sealed balloon filled with air and gently squeeze it in the middle what happens? What changes? What remains the same? If the balloon was filled with water instead of with air, would it behave the same way? Explain. If the balloon was filled with water and then frozen solid, what would happen when you squeezed it? 2. Obtain a large, plastic syringe and draw 25 mL of water into it. Eliminate any bubbles of air. Place the opening of the syringe securely against a rubber stopper or cork. Push down on the plunger of the syringe without allowing water to leak from the syringe. Describe how the volume of the water changes with an increase in pressure. Repeat the above procedure using 25 mL or air. How does the volume of air change with an increase in pressure? Try to explain the reason for any differences you may have observed. The properly you have just investigated is called compressibility. What must be happening to particles when a material is compressed? How do you think the compressibility of a solid compares to a liquid or gas? Why?Exploring the Chemical World, PGCC, 2003 107 3. Liquids are fluids, that is, they have the ability to flow or pour. Are gases fluids? You are going to verify your response by trying to pour a gas. The problem that arises is that you cannot see a clear, colorless gas and therefore how can you tell whether or not it is pouring out of a container! We could use a gas that has a color, but many colored gases such as chlorine (green) and fluorine (yellow) are toxic. The simple solution utilizes an observation you made in the Investigation of Chemical Reactions laboratory. What happens to a burning splint when it comes into contact with carbon dioxide? First you have to produce some CO2. Place about 1 gram of sodium bicarbonate (sodium hydrogen carbonate or baking soda) into the bottom of a Florence flask. Add 25 mL of dilute acetic acid (vinegar). Quickly cover the mouth of the flask with a glass plate so the gas can accumulate before you attempt to pour it. Light a small candle, remove the glass plate and carefully pour the gas onto the flame. Do not allow any liquid to leave the flask! If you get no result try adding a small amount of additional reactants into the flask and try again. Based on your observations are gases fluids? Explain. 4. Obtain a room deodorizer, place it on one end of the lab bench, and open it carefully. Record how long it takes for you to detect the odor. What state of matter is the deodorizer material? Explain how the vaporized molecules (causing the odor) from the deodorizer reached your nose.Exploring the Chemical World, PGCC, 2003 108 5. When bubbles of a gas form in a liquid, what do they do? (Visualize a carbonated drink) Why? Think about walking in knee deep water, or moving your legs while lying in a bath tub filled with water. Now think about walking in air. Which is easier and why? Water has a density of about 1g/mL at room conditions. Estimate the density of air at room conditions. Why does a helium balloon rise when it is released? What would a balloon full of carbon dioxide do if you released it in a room full or air? Why? The density of a gas depends on its molar mass. Under the same conditions, gases with molar masses less than air will float, while those with molar masses greater than the molar mass of air will sink in air. Air has the equivalent of a molar mass of 29 g/mole. How do you think that value was obtained? Helium behaves just like carbon dioxide towards burning objects. Suppose you were to repeat procedure 3 with a flask of helium instead of carbon dioxide, what would happen? Why? 6. Place a 400 mL beaker with 300 mL of tap water onto a hot plate. Suspend a thermometer from a clamp into the beaker such that it does not touch the bottom. Start to warm the water to between 60-80oC. Do not stir or disturb the water as it warms up.Exploring the Chemical World, PGCC, 2003 109 Describe the beaker before, during, and after warming. Look at the bottom and sides of the beaker. Devise an explanation for any phenomenon you observe. Gently tap the beaker. What happens and why? Heat the beaker of water to boiling. Describe what is happening as the water boils. What are some differences when compared to warming? Keep the beaker of water for later in this lab activity. 7. Inflate a balloon with air to a diameter of about 10 cm and seal it. Why did the balloon expand in size when you inflated it? How could you determine the volume of air in the balloon? (Describe at least 2 ways.) Place the balloon in a bell jar. If available also add some shaving cream and fresh marshmallows. Ask the instructor for help if you are unfamiliar with this apparatus. The motor of the vacuum pump will remove air from the bell jar when it is turned on. Make a prediction about what you think will happen to the balloon as air is removed from the bell jar. Why did you make that prediction? Turn on the vacuum pump and observe. What happens to the balloon? Did the amount of gas in the balloon change?Exploring the Chemical World, PGCC, 2003 110 Formulate an explanation for what you observed. Keep the balloon for #9. 8. Let’s explore this relationship