Experiment
6-1
The Gas Laws
Lab Report = 150
Introduction:
In part 1 of this experiment, a given quantity of gas will
be trapped in a syringe. The pressure on this gas will
then be increased by placing weights (books) on top of
the plunger of the syringe. The total pressure acting on
the gas consists of the weight of the books plus the
weight of the atmosphere acting on the syringe.
Symbolically we write:
Total pressure = pressure due to books + pressure due
to atmosphere
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Objectives:
1. Observe the effect of increasing pressure on the
volume of a confined gas.
The volume of the gas will be recorded for each of the
pressures used. The data (values for pressure and
volume) will be plotted on a graph in several ways in
order to find a simple mathematical relationship between
pressure and volume.
In part 2 of this experiment, a given quantity of gas will
again be trapped in a syringe, but this time we will keep
the pressure constant and change the temperature by
immersing the syringe in a water bath.
2. Observe the effect of increasing temperature on the
volume of a confined gas.
3. Construct a volume-temperature graph from the
collected data and determine from the graph the
volume of a gas at absolute zero.
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Equipment: Safety glasses
1 30-35 mL sealed syringe
1 set of support blocks
5 "standard" books
600 mL beaker
temperature probe or thermometer
tongs
ice
hot plate
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Experiment 6-1
Page 1
Precedure:
Part 1
1. Adorn your laboratory apron and safety glasses.
1. As in part 1, set the syringe plunger to about
75% of capacity.
2. Pull the syringe out 5 ml and let it snap back.
2. Measure the barometric pressure of the room
atmosphere and record this value in the data table.
Convert this pressure to kiloPascals.
3. Read the syringe and place the value on line 1
under Volume OUT in the data table.
3. Separate the syringe cylinder from the piston, and
measure the internal diameter of the cylinder.
Calculate the radius of the cylinder and the crosssectional area.
4. Push the plunger in 5 ml and let it snap back.
4. Measure the mass of the piston
6. Average the two readings and place the value
under volume average.
5. Set up your ring stand with utility clamp. You will
clamp the plunger in the middle to give support. Make
sure you don’t twist too hard on the clamp so you don’t
change the volume of the plunger.
7. Record the room temperature on line 1 under
temperature.
6. Set the plunger of the syringe to about 90% of
capacity by removing the cap and placing the plunger
at 90% capacity, place the cap back on. If the plunger
binds on the sides of the syringe, remove the plunger,
apply a very thin layer of glycerol to the rubber seal,
and reinsert the plunger. Place the syringe in the
support blocks. Tap the syringe several times, then
record the volume of the trapped gas to the nearest 0.1
mL and the relative pressure as 0 "books". Tap again
and read again. And again. Then average the values.
6. Carefully center a text book on top of the plunger.
(any textbook will do, but you will need five copies of
the same textbook to complete the experiment.) Tap
the book several times, then record the volume of the
gas trapped in the syringe when a load of one book is
on the plunger. Repat twice and average the results.
One team member will probably have to help balance
the books, try not to put extra pressure on the books.
7. Now add another textbook and carefully determine
the volume three times and record the data. Continue
in this manner until a pressure of 5 books is obtained.
Part 2
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Experiment 6-1
5. Read the syringe and place the value on line 1
under Volume IN in the data table.
8. Place the syringe in the ice bath for 5 minutes.
Keep it attached to the ring stand. Make sure you
can read the plunger in the water bath, so you
should probably move the plunger to the edge of
the beaker. Keep the syringe in the water while
reading it.
9. Read the syringe as in steps 2-6 above in Part 2.
10. Record the temperature of the ice bath on line 2
under temperature.
11. Place the syringe in a warm (≈40°C) water bath.
You will have to move the clamp up on the ring
stand.
12. Repeat steps 2-6 above to read the syringe.
Keep the syringe in the water while reading it.
13. Record the temperature of the water bath on
line 3 under temperature.
14. Turn the hot plate on high and monitor the
temperature. When it reaches ≈60°C, record the
temperature and volume of the gas in the syringe
as in steps 2-6.
15. Repeat step 14 at ≈80°C and ≈100°C.
Page 2
•Data (20):
Atmospheric pressure: ____________ mm Hg = _______________ kPa
Diameter of syringe cylinder: _____________ cm
Mass of piston assembly: __________g
Weight of Heath Chemistry Text: 4.10 pounds
Table 6.1.1 Pressure and Volume Data
Relative P
(books)
0
1
2
3
4
5
V1 (mL)
V2 (mL)
V3 (mL)
Vavg
1/V (1/mL)
(mL)
Absolute P
(kPa)
P*V (kPa*mL)
% dev
Average
(10)Stamp...........
Table 6.1.2 Volume and Temperature Data
Trial #
IN
Volume (mL)
OUT
Tempe rature
average
oC
oK
(10)Stamp...........
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Use dimensional analysis to show all derivations!
Calculations (30):
Calculation tips: make sure all units are in SI base
units such as length in meters, mass in kilograms,
and pressure in Pascals. Weight is in Newtons
(2) 1. In part 1, the total force acting upon the confined
air volume when no weight is on the block is equal to
the sum of the atmospheric pressure and the weight of
the upper support block and piston. The downward
force (weight) exerted by any object is equal to the
product of its mass and the acceleration due to gravity
(9.81 m/s2). To determine the contribution of the block
and piston assembly, the weight of this unit must be
divided by the surface area in contact with the confined
air volume. Since you measured the internal diameter
of the cylinder, the area in contact with the piston may
then be derived using the formula, A = πr2.
Experiment 6-1
Calculate the internal radius of the cylinder
(diameter/2).
(2) 2. Calculate the area of the cylinder/piston interface
in m2.
(2) 3. Use the mass of the piston to calculate the
downward force (weight) of the piston (weight = mass *
acceleration due to gravity).
(4) 4. Convert the weight of the piston-block assembly
to pressure in kPa. (Pressure = force/area). Remember
pressure would be in Pascals because N/m2 is a
Pascal therefore you need to show conversion from
Pascal to kilopascal.
(2) 5. Find the pressure exerted by the atmosphere
and the piston-block assembly on the trapped gas (air).
Page 3
Total pressure = atmospheric pressure + pressure due
to piston-block assembly.
(4) 6. Determine the force exerted by each book. Force
= mass * acceleration due to gravity.
(4) 7. The pressure exerted on the gas by a book is
equal to the weight of the book divided by the surface
area in contact with the gas. Calculate the pressure in
kPa and record it.
(4) 8. Calculate the sum of the appropriate "book"
pressures and add them to the total "no weight"
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Analysis and Conclusions (92):
Part 1
(20) 1. Construct a smooth graph (Graph 1) of absolute
pressure versus volume on Excel. Be sure to label
axes properly.
(20)2. Graph absolute pressure against 1/V (Graph 2).
Be sure that your horizontal scale starts with 1/V = 0 at
the y-axis. Draw the best straight line through these P
vs 1/V plots, making sure to extrapolate to the y-axis.
(4)3. According to these graphs, what is the
mathematical relationship between pressure and
volume of a gas.
(4)4. Find the average value of P * V, and assume it to
be the correct value. Then find the % deviation for
each of your P*V values. Calculate the average %
deviation.
(4) 5. Have you verified Boyle's Law within reasonable
error? Explain.
pressure to obtain the total pressure acting on the
system. Record the total pressures in Data Table
6.1.1.
(4) 9. Calculate P * V , the product of pressure and
volume, for each set of data, and record your values in
Data Table 6.1.1.
Part 2
(2) 10. Convert each recorded temperature from °C to
kelvins.
Label the temperature scale in both oC and K.
Draw the best straight line that approximates the
data points and use dashes to extrapolate and find
the value of the temperature that corresponds to
the gas occupying no space.
(4)7. The graph would imply that at some cold
temperature the gas would no longer have any
volume. According to your extrapolation, what
would the temperature be when the gas ceased
having volume?
(4)8. How does the value of the x-intercept on the
graph compare with the accepted value of absolute
zero?
(4)9. Is your data consistent with Charles' Law?
Explain.
(4)10. The pressure did not vary during this
experiment because all of the trials were performed
at constant room pressure. If the pressure had
varied, how would it have affected your results?
Explain.
Part 2
(20) 6. Plot a graph (Graph 3)of volume versus
(4)11. What factors might contribute to error in this
temperature on a full sheet of graph paper. Plot
experiment?
temperature as the independent variable (x-axis)
and volume as the dependent variable (y-axis).
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Synthesis (8)
(4)1. If a helium filled balloon is released at the earth's
surface, what is it's eventual fate? Explain!
(4)2. Aerosol spray cans should never be thrown into
fires or disposed of in incinerators. Explain!
Experiment 6-1
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