Discovery Lab Gas Laws

Discovery Lab: Gas Laws Purpose To discover the relationships between temperature, pressure, volume and how they influence gas laws. Your task As you complete the following experiments try to determine the relationships between two of the following: temperature, pressure, and volume. Do not worry about getting everything right just make observations and be able to explain your decisions. You have about five minutes for each station. Materials Erlenmeyer flask Balloon Syringe Marshmallow Soda Can Hot Plate Safety Precautions Do not eat or drink anything in the lab Wear eye protection Be VERY careful with the hot plates and the boiling water! Experiments Balloon Station Procedure Add about 20mL of water to a 125mL Erlenmeyer flask. Place a small balloon over the opening of the flask and place the flask on the hot plate until the water boils. When the balloon performs its trick, remove flask WITH TONGS soon after so that you do not get scalded with hot water! Observations Balloon filled with air a) What happens to the balloon? The balloon filled with air when the flask was heated. b) Circle the variables you are dealing with: temperature pressure volume c) Complete these phrases: As Pressure _____increases__ Temperature ____increases____ (increases or decreases).→ Directly Proportionate As Temperature ___increases_____ Volume ___increases___ (increases or decreases). →Directly Proportionate d) Mark the above relationships as inversely or directly proportionate. Marshmallow Station Procedure Place a marshmallow in a syringe. Push and pull the syringe while sealing the end of the syringe by putting your finger on it. Observe what happens to the marshmallow. Observations Include a picture. Pushed= wrinkly marshmallow Pulled= puffed up marshmallow a) b) c) d) When I push the syringe, the marshmallow the marshmallow shrinked (like a raisin). When I pull the syringe, the marshmallow the marshmallow expanded. Circle the variables you are dealing with: temperature pressure volume Complete this phrase: As Pressure ____increases__ Volume __decreases__ (increases or decreases). e) The relationship between these variables is _inversely_ proportionate. (inversely/directly) Soda Can Station Procedure Add a small amount of water to the soda can and place it on a hot plate until the water is boiling. Then place the tongs firmly around the can and quickly flip it into the ice water bucket. Observations The water in the can boiled. When it was turned over into the ice tub, the can was crushed. a) What happened to the can? The can was crushed. b) Circle the variables you are dealing with: temperature pressure volume c) Complete these phrases: As Pressure _increases_ Volume _decreases__ (increases or decreases).→ INVERSELY As Temperature _increases_ Volume _increases_ (increases or decreases).→DIRECT As Pressure _increases_ Temperature _increases_ (increases or decreases).→ DIRECT d) Mark the above relationships as inversely or directly proportionate. Additional Investigation Observe the following experimental data concerning a container of gas. The data was obtained by making measurements of the pressure, volume and temperature of a sample of a gas. Several different kinds of gases were used and all had identical results. The variable that was not changed was the amount of gas present. The number of moles of gas always remained the same during these trials. Trial A B C D E F G Pressure (P) Units: kPa (kilopascals) 120 135 195 150 135 100 225 Volume (V) Units: L (liters) 3.2 2.5 2.3 2.0 4.2 3.0 3.2 Temperature (T) Units: K (Kelvin) 324.3 285.0 378.7 254.4 480.8 254.4 608.0 H 262 2.8 620.4 1. Verify that this equation is true when the volume is unchanged: P1/T1 = P2/T2 (Hint: You must use two sets of data where the volume does not change. I.E. Trial A and G. In the equation, subscript 1 refers to the pressure and temperature for the first trial you select and the subscript 2 refers to the pressure and temperature for the second trial you select.) 2. Scientists often look for relationships between variables. If you want to see how the volume and pressure are related you would need to compare data from different trials when the temperature does not change. Why? If you are changing three variables at the same time it is impossible to compare two variables. You cannot analyze the cause and effect between pressure and volume if temperature is also a factor. How would you be able to tell what caused the change? 3. Find two sets of data in the table that have constant temperature. Which of the following mathematical relationships is true (there may be more than one) when the temperature remains unchanged? This relationship is known as “Boyle’s Law,” named after the person that first discovered it. a. P1/V1 = P2/V2 b. (P1)(V1) = (P2)(V2) c. P1 + V1 = P2 + V2 d. P1/P2 = V1/V2 4. At constant pressure, which of the following equations is/are true? This relationship is known as “Charles’s Law,” named after the person who first discovered it. a. V1/T1 = V2/T2 b. (T1)(V1) = (T2)(V2) c. P1 + V1 = P2 – V2 5. Complete the following. You may want to consider the equations from your last three questions. a. At constant volume, as the temperature increases, the pressure always _increases_. b. At constant temperature, as the volume increases, the pressure always _decreases_. c. At constant pressure, as the temperature increases, the volume always _increases_. 6. If the volume was not constant, is the statement in 5a always true? Justify your answer by citing experimental data from the data table. No. If the volume was not constant, then no, pressure would remain the same and volume would increase. 7. If the temperature or pressure is not constant are your statements in 5b and 5c correct? Justify your answer. No. If the temperature or pressure are not held constant than the other two variables cannot be directly compared because there are too many factors influencing the changes making it impossible to tell which is causing the change. 8. Would the equations you discovered still be true if the temperature was measured in degrees (ºC) instead of Kelvin (K)? Justify your answer. (Hint: K = ºC + 273) No. Temperature must be in Kelvin. 9. Which of the following quantities does not change when you use the data from different trials? a. PV/T b. PV + T c. PT/V 10. Based on your answer from question 9, verify that this equation is true: P1V1/T1 = P2V2/T2. This equation is called the “Combined Gas Law.” Notice that it contains all of the equations combined into one. . 11. What needs to remain constant in order for the “combined gas law” to be true? (You may need to refer to the information given above the data table) The number of moles must be constant in order for the “combined gas law” to be true. 12. Prove that when the temperature remains constant, the combined gas law becomes Boyle’s law. 13. Prove that when the pressure remains constant, the combined gas law becomes Charles’s law. 14. You have discovered new mathematical relationships among gases. Now is your chance to practice using these equations. a. At constant pressure, the volume of a gas expands from 4.0L to 8.0L. If the initial pressure was 120kPa and the initial temperature was 35C, what is the final temperature? (Hint: PV=nRT and number of moles is constant. R= 8.314L kPa K−1 mol−1) P1=120 kPa P2=120 kPa V1=4.0 L V2=8.0 L T1= 35°C+273=308 K T2=??? b. At constant pressure, a gas is heated from 250K to 500K. After heating, the volume of the gas was 12.0L. What was the initial volume of the gas? P1=Constant Pressure V1=??? L T1= 250 K P2= Constant pressure V2=12.0 L T2=500 K c. The volume of a gas was originally 2.5L; its pressure was 104kPa and its temperature was 270K. The volume of the gas expanded to 5.3L and its pressure decreased to 95kPa. What is the temperature of the gas? P1=104 kPa V1=2.5 L T1= 270 K P2=95 kPa V2=5.3 L T2=???