**Charles Law Lab**

**Quantitative – 50 points**

**Purpose: ** To find
absolute zero. The temperature at which
all molecular motion stops.

**Pre Lab Questions:**

1. Temperature is a measure of the average ___________ of molecules.

2. A very massive gas molecule traveling at the same velocity as a
lighter gas molecule will have a **greater**
or **lesser** kinetic energy?

3. What is the mathematical formula for kinetic energy (abbreviation
KE)? (look on p. 304)

4. Explain the difference between the velocity of a gas particle and
its kinetic energy?

5. Air molecules (N_{2}
gas) move at approximately 1150 miles per hour at room temp (25^{o}C). How come we are not annihilated by these
flying air molecules banging into us?

6. At room temperature, are **ALL**
air molecules moving at 1150 MPH?
Explain.

7. Charles’ law says: If
pressure remains constant, as
temperature decreases, volume ________

8. Assume you have collected 50 mL of air over water in a
container. The water’s temperature is
25^{o}C. 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 (P_{atmospheric}).

a. What is the
pressure of just the dry gas in kPa? (P_{dry gas})

b. Use Boyle’s
Law to solve for a __corrected volume__ of the dry gas: (solve for V_{corrected})

P_{dry
gas}V_{uncorrected} = P_{atmospheric}V_{corrected}.

9. Why can you not just assume that all 50 mL of air in the
container (from problem #8) are just air molecules? (look at the table of water
vapor pressures on p. 899 of your textbook if you need help)

10. 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?**

Would you expect the pressure
inside the container to be:

a. greater than outside air
pressure, b. less than outside air pressure
c. equal to outside air
pressure. **WHY?**

11. Assume the same thing you did in #10, 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?**

Would you expect the pressure
inside the container to be:

a. greater than outside air
pressure, b. less than outside air pressure
c. equal to outside air
pressure. **WHY?**

** **

**What might be on the Pre-Lab Quiz?**

How hot should the water be in the 600 mL flask? How do you stabilize the water temp? Should the Erlenmeyer flask be wet inside or completely dry?

** **

**Lab Table Set-up will look like:**

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**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 70^{o}C and 90^{o}C. Let the water stabilize (turn off the heat
when you reach between 70-90^{o}C.
This will let it stabilize)

3. Place your **EMPTY** (NO WATER IN IT!!! AND IT SHOULD BE VERY DRY INSIDE!!!!!!)
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.

4. Allow the Erlenmeyer flask to heat up for about 2 minutes.

5. **Record** the temperature
of the water at the end of these 2 minutes as **T _{1}.**

6. Place your finger over the tube and remove the Erlenmeyer flask
from the beaker of hot water

7. 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!!!!!!

8. 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.

9. 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 **T _{2}.**

** **

10. Pour that water out of the Erlenmeyer flask and into a graduated
cylinder to record its volume. **Record ** this as **V _{water. }**

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11. 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 **V _{1.}**

** **

12. Determine the V_{2} of gas (V_{2} is the amount
of gas after the temperature is decreased from T_{1} to T_{2}),
use the following equation: V_{2}
= V_{1} - V_{water. Record as V2uncorrected on your Data Table.}

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**PLEASE READ THIS BEFORE RECORDING ANY DATA:** THE DATA TABLE NEEDS TO BE DONE ON A __SEPARATE
SHEET OF PAPER. 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)

V_{1} _____________mL

T_{1} ___________^{o}C ______________K

T2 __________^{o}C
______________K

V_{water}
____________mL

V_{2uncorrected} _____________mL

Room Pressure ________mm Hg (look on barometer in front of room – multiply by 10 since it
is in cm)

Water’s vapor pressure at T_{2}
______________mm Hg (look on p. 899 of textbook)

Pressure of dry gas alone (Room pressure – Water vapor pressure at T_{2})
____________mm Hg

V_{2corrected } ________________mL (see calculation #1 for how to figure
this one out)

V_{1experiment}
_______________mL (see calculation #2 for how to figure this one out)

How
to calculate V_{2corrected}

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**Calculations:**

1. You need to calculate the
value of V_{2corrected. }You
may be wondering: What is V_{2corrected}? Well, I’ll tell you: V_{2corrected }is the volume the DRY
GAS would occupy at standard room pressure (760mm or 101.325kpa). The V_{2} you found by subtracting V_{1}-V_{water}
is the volume of **BOTH** the DRY GAS and the WATER VAPOR (see my beautiful
sketch above). You need just V_{2}
of the DRY GAS. I call this V_{2corrected}

How do you do this?

STEP 1: V_{2uncorrected} = V_{1}-V_{water}

STEP 2: Go to the barometer in the front of the room
and find the room pressure in mm of Hg.
**Record** this as **room** **pressure** on your data table (record in both mm of Hg and kPa). This is P_{atmospheric}.

STEP 3: Use the procedure you used in the pre-lab
(question #8). GO BACK AND LOOK AT THAT
QUESTION RIGHT NOW. Do you recall how
to find P_{drygas}? (Hint: It has something to do with the barometric
pressure of the room, Subtraction, and the chart on p. 899)

P_{dry
gas}V_{2uncorrected} = P_{atmospheric}V_{2corrected}.

**Record** this answer as **V _{2corrected}
**on your data table.) SHOW YOUR WORK
FOR DETERMINING V

2. Using your values for T1, V2corrected
, and T_{2} **(Temperatures in Kelvin!)**, use Charles’ Law (V_{2}T_{1}=V_{1}T_{2})
to solve for V_{1experiment}.
Do this for each of your three trials.
Record this answer as V_{1experiment }on your data table. Again, don’t forget your values for temperature
must be in KELVINS when you use Charles’ Law.

What is V_{1Experiment}? Glad you asked…. You found V_{1} by filling the Erlenmeyer flask
completely with water and dumping it into a graduated cylinder. As it turns out, this is not a very accurate
way to do this. Therefore, to be more
accurate, we use Charles’ Law and the data we collected to get a better value
for V_{1}, I call this better value:
V_{1experiment}. You
should find that the answer you get to this calculation should be pretty darn
close to the one you got from filling the flask with water and measuring it in
the Erlenmeyer flask.

**Graph: **

** **

Plot a graph of (T_{1,}V_{1experiment }) and (T_{2,}
V_{2corrected}). 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
Graphical Analysis.**

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**Charles’ Law Lab**

**Using Graphical Analysis**

1. Find Graphical Analysis on the desktop and
open it.

2. Double Click on the “x” in the x-column of
data. This is in the upper left hand
corner of your screen. VERY UPPER LEFT
CORNER IF YOU PLEASE!

3. Name it “Temperature”

4. Go down to the UNITS and put in “^{o}C”. (Hint:
If you use INSERT SYMBOL, you will find a “^{o}”

5. Click OK

6. Now click on “y” and title it “Volume” with
units of “mL”.

7. Enter your **numerical**
values for T_{2} in “x” and V_{2corrected} in “y”. Then enter your **numerical**
values for T_{1} in “x” and V_{1experiment} in “y”.

8. Go up to ANALYZE and choose LINEAR FIT. A line should appear through your two points
which tells you the slope.

9. Go up to ANALYZE and choose ZOOM GRAPH
OUT. You want to keep zooming out until
your see the LINEAR FIT line cross the X-axis.
(A cute trick is to click on the magnifying
glass with the negative sign in it on the tool bar along the top.) Notice that the lines DO NOT cross the x axis at 0. In fact, that 0 on the graph represents 0
volume ONLY, it will be a NEGATIVE value for temperature (BELOW zero!)

10.
Once you find the X-Axis intercept, go up to ANALYZE and choose
INTERPOLATE. Now, run your mouse arrow
over the x-axis intercept area and record what value that is. This should be the temperature at which the
volume drops to zero. You will need
this value to answer question #6 in the **POST LAB
QUESTIONS**

11. Now go up to DATA and choose NEW DATA
SET. A new column of x and y will
appear to the right of your original column of data. Click on these “x”s and “y”s and label them as you did
before. Put in your data for your
second trial here.

12. Move your mouse arrow over to the word
“volume” on the **graph**. Double click on it. Now you will need to select DATA SET 2 and
check the box for Volume. What you
should see now is two lines on your graph.
If you can’t see both of them, try ANALYZE and AUTO SCALE GRAPH.

13. Go to ANALYZE and LINEAR FIT for the second
set of data. Where does it hit the
x-axis? (HINT: If a box comes up and asks you which lines
you want to linear fit, you just click on all of them and then it will linear
fit each one).

14. Now do this again with your 3^{rd}
set of data.

15. When you are all done, call over Mr. Young
for inspection.

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**Post-Lab Questions:**

1. Find the
difference between V_{1} and V_{1experiment} 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 V_{1experiment} and V_{2corrected}. . 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!)

Here are some values you will
need to solve PV = nRT: **R= 0.0821**
and **P = 1 atm**. 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 V_{1experiment}
at a temperature of T_{2} (room temp)?

b. How many moles of air were in V_{1experiment}
at a temperature of T_{1} (hot temp)?

c. How many moles
of air were in V_{2corrected} at a temperature of T_{2} (room
temp)?

3. What do you notice about the answer to 2b. and 2c? What is significant about these answers?

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 V_{2uncorrected} and V_{2corrected}. 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?**

** **

1. **Pre-Lab Questions:**
Questions and answers to Pre-lab (you can just copy-paste the questions
from this lab onto a Word file and then type in your answers).

2. **Data tables:** Three
data tables (one for each trial). You
could just write down all of the information in a column on the extreme left
hand side of your paper and then make three columns titled “trial #1”, “trial
#2” and “trial #3”.

3. **Calculations:** You
need to do calculations #1 and #2 three times (one for each trial). Please make sure they are separated by trial
so I can easily read them and figure them out.

4. **Graph:** Plot a graph according to the
instructions. It **MUST** be on
graph paper. Your axis’ must be labeled
and include numerical values along the axis.

5. **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!

Overall, neatness
counts! Please do a good job on this lab!