Lab 4A Putting Bubbles to the Test

Transcription

1 Lab 4A Putting Bubbles to the Test Safety Note Wear safety goggles and aprons. Suppose you want to measure the length of an aardvark s eyelash. You first have to catch an aardvark. Likewise, if you want to learn about the gas that is produced when shell and HCl are mixed, you must have a sample of it. That s your task in the first part of this lab. Collect some of this gas and learn more about it. It will take about 10 minutes for you to learn a rather tricky way to catch a sample of gas. You will need to work with your lab partner during the gas collecting activity. To start, you will need the following equipment from the supply area: 1. 1 length of tubing 2. 2 plastic straws; 1 for each lab partner 3. 1 plastic bucket 4. 1 baby food jar 5. 1 vinyl square You will use the baby food jar as a container for the gas from the HCl-shell mixture. But you have a problem to solve first. Question 1 What gas is already in the baby food jar? You need a way to keep from mixing the gas you want to collect with the gas already in the jar. Here s how you do it. Activity A Half fill the plastic bucket with tap water. Put it on your lab table. Activity B Sink the uncapped baby food jar into the water. Be sure the open end is up. Keep the jar under water. Invert it and set it on the bottom of the bucket. Question 2 What happened to the air that was in the baby food jar?

2 You aren t quite ready to collect the gas from the HCl-shell mixture. First you need some more experience in collecting gas. Activity C Push a straw into one end of the tubing. Slip the other end of the tubing just under the open end of the baby food jar. Be sure to hold the jar and tubing in place. Do not press down on the tubing or you might pinch it closed. Blow gently into the straw for a few seconds. Question 3 What happened to the water inside the baby food jar as you blew through the straw? Question 4 Where did the gas from your lungs collect as you blew through the straw? Question 5 Blow into the jar until it is full of gas. Continue blowing into the jar. Describe what happens. Question 6 What happens to the gas in the jar under water if you turn the open end up? Remember, you are going to catch gas from the HCL-shell mixture. You must also be able to hold it in the jar. Activity D Take the next few minutes to practice filling the baby food jar with the gas from your lungs and placing a vinyl square lid on it to capture the gas. As demonstrated by the teacher, slowly bring the jar and vinyl square lid out of the bucket and turn it over without losing the gas. Take turns with your lab partner. Be sure to show the teacher each gas capture. The best captures will have the least amount of water in the baby food jar when placed on your lab table. STOP here and wait for further instructions

3 You ve been successful in collecting and holding a sample of the gas from your lungs. You got it by letting the gas bubble into the jar and push the water out. You can use the same procedure to collect the gas produced when shell and HCl are mixed. Watch the teacher demonstration. Then gather the following equipment from the supply area: ml flask 2. 1 scoopful of crushed shells funneled into the flask 3. 1 rubber stopper with tubing 4. 2 additional baby food jars 5. 2 additional vinyl squares ml beaker of HCl ml (small) air piston Activity E Gently push the rubber stopper with tubing onto the top of the flask. Activity F Put the tip of the small air piston into the HCl beaker making sure that the plunger is all the way down. Keep the tip of the piston under the surface as you fill it. This will keep air out of the piston. Now fill the piston to the 30 ml mark by slowly pulling up on the plunger. Do not overfill or remove the plunger from the piston. Check to be sure that there are no air bubbles in the piston. If there are, gently push the plunger all the way down and repeat this activity until the piston is filled without getting air trapped in it. Activity G Attach the HCl filled piston to the rubber stopper (short tube) as demonstrated by your teacher. Also, make sure that the piston and tubing are firmly attached to the rubber stop to avoid leaking HCl. The apparatus should now stand up without tipping over. Place it and the remaining HCl beaker toward the center of the lab table, away from the edge, to avoid knocking it onto the floor. You are now ready to begin collecting gas. You will fill each of the three jars. Activity H Put the free end of the long rubber tube under the water into the bucket. Do not put it under the jar. Then slowly add 5ml of HCl to the shell. Do this by pushing the plunger of the piston down to the 25ml mark. (Do not add the entire plunger of HCL at one time.) Let the gas bubble from the rubber tube

4 for about 15 seconds. This will remove all the air that is trapped in the flask and rubber tube. Activity I Slip the end of the tube in the bucket just under the mouth of one of the inverted baby food jars. As the bubbling in the flask slows down, add another 5ml of HCl to the flask in order to keep the bubbles flowing through the tube. When bubbles arise to the surface indicating the jar is filled with gas, remove the tube from the jar (but keep the tube deep in the water), and slip a vinyl square under the jar mouth to act as a lid. Lift the jar and lid out of the bucket, flip it mouth side up keeping the vinyl square lid on tight, and place it on your lab table. Repeat this activity 2 more times so that you have captured 3 jars of gas. Once on the lab table, do not remove the vinyl square lids or the gas captured will escape. After collecting three jars of gas and awaiting further instructions, please do the following as a partial clean up: DO NOT TOUCH YOU 3 JARS OF GAS 1. Gently remove the air piston from the stopper & empty remaining HCL from the air piston into the HCl beaker and return the HCl beaker to the fume hood 2. Take the flask with reacting shells & HCL to a sink and add water to ½ way fill the flask. DO NOT POUR SHELLS INTO THE SINK!! 3. Swish & pour the entire contents of the flask into the special waste container. Rinse and repeat as needed. 4. Return the flask to the supply area 5. At your lab table drop the rubber stopper with tubing into the bucket of water for a rinse 6. At your lab table drop the air piston into the bucket of water and plunger it for a quick rinse 7. Take the bucket to a sink & pour the water from the bucket down the sink. Then return the bucket, rubber stopper with tubing and air piston to the supply area where you first got it. 8. Use paper towels to wipe and dry your lab table 9. Throw used paper towels into the trash You are now ready to do what you started out to do in the lab. You will learn more about the gas from the mixing of HCl and shell.

5 Question 7 Look at the 3 jars of gas & ignore any liquids. Does the gas have a color? Question 8 Could the gas collected be air? It is possible to test the gas to see if it is air. You need only compare the behavior of air with that of the gas in the jars. As you compare air and the gas, you should treat them both the same. Do they behave differently when treated the same? If they do, then they must be different gases. Do they behave alike when treated the same? If so, they are probably the same gas. Did you treat them exactly the same way? If not, you can t be sure if the gas and air are alike or different. You should now make the same tests on air and on the unknown gas. STOP here and wait for further instructions Activity J As directed, go get two 50ml beakers from the fume hood. One is a clear liquid called limewater. The other is a red/pink liquid called Phenol red. Place them on your lab table. Question 9 What happens when limewater is mixed with air (open container)? Question 10 What happens when Phenol red is mixed with air (open container)? Activity K On teacher direction only, take one jar for testing with limewater. Quickly slide the vinyl lid aside, dump in all the limewater, and slide the lid closed. Holding the lid on tight, gently shake the jar. Question 11 Describe what happened when limewater was shaken with the jar of unknown gas? You may be ready right now to decide whether or not the unknown gas is air. But more evidence will give you more confidence in your conclusion.

6 Activity L On teacher direction only, take the second jar for testing with Phenol red. Quickly slide the vinyl lid aside, dump in all the Phenol red liquid, and slide the lid closed. Holding the lid on tight, gently shake the jar. Question 12 Describe what happened when Phenol red was shaken with the jar of unknown gas. Activity M On teacher direction only, take the third and final jar. Light a match. Quickly slide the vinyl lid aside and insert the lit match into the jar. Quickly remove the match and slide the lid closed. Do not drop the match in the jar. Question 13 Describe what happened when the lit match was inserted into the jar of unknown gas. You watched a lit match in air and in the unknown gas. Compare their behaviors. In science, being able to tell substances apart is quite important. That is one of the reasons you have collected the unknown gas. You are trying to find out what kind of gas shell and HCl produce. Is it air, or some other gas? So far, you have seen that air and the unknown gas are alike, at least in one way. Both are colorless. However, the two gases have a different effect on limewater, Phenol red, and a lit match. Question 14 In your notebook, complete the following statement: The unknown gas is a material that turns limewater, Phenol red, and causes a lit match to. This completed statement in question 14 is a definition of the unknown gas. More specifically, when I know what gas I have by the tests I performed (operated), I have an operational definition for that gas. Therefore, the operational definition of the unknown gas is the statement in question 14. Clean Up Now that you have finished all lab work, clean and put away your equipment in the supply area as directed. Specifically, 1. Return match boxes to the teacher. 2. Rinse and return the 3 baby food jars to the supply area.

7 3. Rinse, dry and return the vinyl squares to the supply area. 4. Return both the limewater and Phenol red beakers to the fume hood. Do Not Rinse them. 5. Wipe down lab tables with damp paper towels and discard in the trash. 6. Return safety glasses to the cabinet and fold away aprons. 7. Wash hands with soap and water at any of the four sinks. STOP here for today.