Charles Law Lab Quantitative – 60 points (10 points come from pre-lab quiz)
Pre Lab Questions:
1. Temperature is a measure of the average ______of molecules.
2. What is STP? (Standard Temperature and Pressure) for the following:
______oC ______kelvin ______atm ______kPa ______psi ______mm Hg
3. One mole of ANY gas will fit into ______L at STP.
4. A very massive gas molecule traveling at the same velocity as a lighter gas molecule will have ______as the lighter gas molecule
a. the same Kinetic Energy b. a greater Kinetic Energy c. a lesser Kinetic Energy
5. What is the mathematical formula for kinetic energy (abbreviation KE)? (look on p. 304)
6. Explain the difference between the velocity of a gas particle and its kinetic energy?
7. Air molecules (N2 gas) move at approximately 1150 miles per hour at room temp (25oC). How come we are not annihilated by these flying air molecules banging into us?
8. At room temperature, are ALL air molecules moving at 1150 MPH (yes or no)? Explain.
9. Charles’ law says: If pressure and number of particles remain constant, then as temperature decreases, volume ______
a. increases b. decreases c. remains the same
10. Assume you have collected 50 mL of air (Vuncorrected) over water in a container. The water’s temperature is 25oC. At this temperature, water has a vapor pressure of 3.2 kPa. The TOTAL pressure of the gas in the container is 760 mm Hg (Patmospheric).
a. What is the pressure of just the dry gas in kPa? (Pdry gas) (hint: you must convert mm of Hg into kPa first. 101.325 kPa = 760 mm of Hg
b. Use Boyle’s Law to solve for a corrected volume of the dry gas: (solve for Vcorrected)
Pdry gasVuncorrected = PatmosphericVcorrected.
11. Why can you not just assume that all 50 mL of air in the container (from problem #10) are just air molecules?
12. Assume you have a SEALED 250 mL glass container which contains 0.01 moles of air molecules at room temperature. You begin to heat it up over a Bunsen burner. After a few minutes, you decide to count the number of moles of air in the container. Would you expect to find:
a. less than 0.01 moles, b. more than 0.01 moles, c. 0.01 moles. WHY?
13. Would you expect the pressure inside the container (from #12) to be:
a. greater than outside air pressure, b. less than outside air pressure c. equal to outside air pressure. WHY?
14. Assume the same thing you did in #12, except this time, the container has a hole in the top of it. After you heated it up, Would you expect to find:
a. less than 0.01 moles, b. more than 0.01 moles, c. 0.01 moles. WHY?
15. Would you expect the pressure inside the container (from #14) to be:
a. greater than outside air pressure, b. less than outside air pressure c. equal to outside air pressure. WHY?
Lab Table Set-up will look like:
Procedure:
1. Fill your 600 mL beaker with about 250 mL of water - not necessary to be EXACT.
2. Heat the water to a temperature between 70oC and 90oC.
3. Now, fill the empty Erlenmeyer flask up to the top with water. Place the rubber stopper into the
Erlenmeyer so that the water fills the glass tube in the rubber stopper. Pour this water out into a graduated cylinder to record its volume. Record this as V1.
4. Place your EMPTY (NO WATER IN IT!!!!) Erlenmeyer flask into the 600 mL beaker so that it touches the bottom (but do not block the tube coming out of the rubber stopper). You will have to hold the Erlenmeyer flask in the water. Hold it down by putting your fingers on the rubber stopper.
5. Allow the Erlenmeyer flask to heat up for about 2 minutes.
6. Record the temperature of the water at the end of these 2 minutes as T1.
7. Place your finger over the tube and remove the Erlenmeyer flask from the beaker of hot water
8. Turn the Erlenmeyer flask upside down in the bucket of water provided at your table. When the neck of the flask is in the water, remove your finger from the tube. (See drawing A below)
Watch the water rush in! Whoopee!!!!!!
9. When the water stops rushing in equalize the pressure (see drawing B above). Make sure you equalize the pressure by allowing the water level in the Erlenmeyer flask to equal that of the water in the tank.
10. Once the pressure has been equalized, put your finger over the hole in the glass tube and remove the flask from the water. Take off the rubber stopper and take the temperature of the water in the Erlenmeyer flask. Record this as T2.
11. Pour that water out of the Erlenmeyer flask and into a graduated cylinder to record its volume. Record this as Vwater. You can then throw that water away. You don’t need it.
12. Determine the V2 of gas (V2 is the amount of gas after the temperature is decreased from T1 to T2), use the following equation: V2 = V1 - Vwater. Record as V2uncorrected on your Data Table.
PLEASE READ THIS BEFORE RECORDING ANY DATA:NEATNESS COUNTS — REMEMBER YOU ARE GOING TO DO THIS EXPERIMENT AT LEAST THREE TIMES, THAT MEANS YOU WILL HAVE THREE DATA TABLES AND THREE LINES ON YOUR GRAPH.
Data table: (the stuff in ()’s is there to help you. Don’t include it in your write-up)
Trial #1 / Trial #2 / Trial #3V1 (mL)
T1 (Celsius)
T1 (Kelvin)
T2 (Celsius)
T2 (Kelvin)
Vwater (mL)
V2Uncorrected (mL)
Room Pressure (kPa) Mr. Proodian will write this on the front board.
Vapor Pressure of Water at T2 (kPa). Refer to Table of Vapor Pressures
Pressure of Dry gas alone (kPa). (Room Pressure) - (Water Vapor Pressure) = Pressure of Dry gas alone.
V2Corrected (mL). See calculation #1 (on next page) for how to figure this one out.
V1experiment (mL) See calculation #2 (on next page) for how to figure this one out
Calculations:
CALCULATION #1: How to figure out V2corrected. You may be wondering: What is V2corrected? Well, I’ll tell you: V2corrected is the volume the DRY GAS would occupy at standard room pressure (760mm or 101.325kpa). The V2uncorrected you found by subtracting V1-Vwater is the volume occupied by BOTH the Pdry gas and the Pwater vapor(see my beautiful sketch above). You need just V2 of the Pdry gas. I call this V2corrected
Remember that the Pdry gas can be found by subtracting the Pwater vapor (from the water vapor table) from the Ptotal of the room (the atmospheric pressure). (Pdry gas = Ptotal of room - Pwater vapor at T2)
Water-Vapor Pressure Use this table to find Pwater vapor at T2
Temperature / kPa / mm Hg / Temperature / kPa / mm Hg20oC / 2.34 / 17.5 / 24 oC / 2.98 / 22.4
21 oC / 2.49 / 18.6 / 25 oC / 3.17 / 23.8
22 oC / 2.64 / 19.8 / 26 oC / 3.36 / 25.2
23 oC / 2.81 / 21.1 / 27 oC / 3.57 / 26.7
If you do not see your temperature (T2) above, then please refer to the more complete table available on the back of the periodic table paper we use when taking tests in class.
How do you then calculate V2corrected? Use this equation below and solve for V2corrected
Pdry gasV2uncorrected = ProomV2corrected.
Record this answer as V2correctedon your data table. SHOW YOUR WORK FOR DETERMINING V2corrected.
Calculation #1: Finding V2corrected
Trial #1 / Trial #2 / Trial #3Pdry gasV2uncorrected = ProomV2corrected / Pdry gasV2uncorrected = ProomV2corrected / Pdry gasV2uncorrected = ProomV2corrected
CALCULATION 2: How to figure out V1experiment. Using your values for T1, V2corrected , and T2(Temperatures in Kelvin!), use Charles’ Law (V2correctedT1=V1experimentT2) to solve for V1experiment. Do this for each of your three trials. Record this answer as V1experiment on your data table. Again, don’t forget your values for temperature must be in KELVINS when you use Charles’ Law.
What is V1Experiment? Glad you asked…. You found V1 by filling the Erlenmeyer flask completely with water and dumping it into a graduated cylinder. After the water rushed in, you subtracted Vwater from V1 to find V2uncorrected. It was uncorrected because the gas sitting above the water contained dry gas as well as water vapor. You then did the calculation to determine how much of V2uncorrected consisted of just the dry gas (calculation #1)
But now, we have to think about these molecules of dry gas sitting in the original empty flask while you were heating it. Before the glass was heated, there were “n” number of molecules of gas inside. While you were heating the flask, however, many of those molecules escaped out the top so now you have “n-number that left” number of molecules in the flask. Let’s assume you have a flask with a V1 of 256 ml. All of those “n-number that left” number of molecules are moving around in that volume but they have a higher pressure than the outside air so in essence they would occupy a smaller volume than 256 ml if they were at room pressure. V1experiment is the volume they would occupy at room pressure. It will be less than V1, but not by very much if the pressure has a chance to equalize before you put the flask over in the cold water bath.
Calculation #2: Finding V1experiment
Trial #1 / Trial #2 / Trial #3(V2correctedT1=V1experimentT2) / (V2correctedT1=V1experimentT2) / (V2correctedT1=V1experimentT2)
Graph:
Plot a graph of (T1,V1experiment ) and (T2, V2corrected). The Temperatures are on the X-axis and the Volumes are on the Y-axis. You will have three lines on your graph – because you did the experiment three times. The following will help you plot this graph using a program called Logger Pro.
Post-Lab Questions:
1. Find the difference between V1 and V1experiment for each of your three trials. (eg. Subtract the two values)
2. Using PV=nRT you should be able to figure out how many moles of air were in V1experiment and V2corrected. . You solve for n(which is the number of moles of gas). (Do a-c for each of your three data tables. Arrange them nice and neat! Have a-c for one trial together, then do the next a-c, then the next one. DON’T mix them all together!) SHOW YOUR WORK!
Here are some values you will need to solve PV = nRT: R= 8.314 and P = 101.325 Kpa. Temperature is in Kelvins. The values you will use for V and for T are given in a-c below.
a. How many moles of air were in V1experiment at a temperature of T2 (room temp)?
b. How many moles of air were in V1experiment at a temperature of T1 (hot temp)?
c. How many moles of air were in V2corrected at a temperature of T2 (room temp)?
3. Why do you think 2b and 2c are the same number of moles? Draw a picture of what the Erlenmeyer flask looks like when it is in the situation of 2b (at its hottest temperature. Include dots for air and shading for any water, if there is any water). Draw a picture of what the Erlenmeyer looks like when it is in the situation of 2c (at its coldest temperature. Include dots for air and shading for any water, if there is any water). I want an explanation and a drawing!
4. Why did you have to put the Erlenmeyer flask under the water so that the water levels were equal inside and outside the flask BEFORE you put your finger over the glass tube and pulled out the flask? What would be the result if you had the water level in the flask higher than the water in the bucket? What about if it were lower?
5. Why does water come rushing into the flask when you turn it over into the water? Use drawings to explain your answer. Remember that the pressure of the room pushes down on the water.
6. According to your graph, what is the temperature (in Celsius and Kelvin) at which molecular motion is going to be zero (in other words, zero volume).
7. What is the difference between V2uncorrected and V2corrected. In other words, what do you have to correct for? I want to know why you have to correct the volume.
What is due for this lab? Lab should be in this order:
Pre-Lab: (Only a few questions will be graded for points, but I won’t tell you which ones before you turn in the lab. That way you will do all of them.) Total: (10 pts)
Data Table and Calculations:You may write your calculations by hand, no need to type them on the computer But make sure they are in the Boxes provided for the Calculations. Total: (10 pts)
Data Table Three trials shown with units (4pts)
Calculation #1: Three trials with work shown (3pts)
Calculation #2: Three trials with work shown (3 pts)
Post-Lab Questions: Write the questions and then answer them (again, COPY-PASTE is the way to go!). Show your work for #2 – it is a very important question so don’t skip it!(Only a few questions will be graded for points, but I won’t tell you which ones before you turn in the lab. That way you will do all of them. Obviously, Question #2 will be one of the ones I’ll grade) Total: (10 pts)
Logger Pro: The following will help you plot this graph using a program called Graphical Analysis.
Three lines are shown on the graph
Axis are labeled correctly (y = volume, x = temperature) (5pts)
y=mx+b formula listed on graph three times (one for each line) (5pts)
Data table for each of the three lines is shown (5 pts)
Graph is zoomed out and the three lines cross the x at around -273 (5 pts)
Total: (20 pts)
Other Factors that would bring down the grade:
-20 points if late
-20 points if messy
-25 points from Logger Pro if it is an exact duplicate of someone else’s Logger Pro
½ credit if copied from another person's paper or graph