CLASS SET
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Unit 9 Lab: Volume of a Mole of Gas
Purpose
The purpose of this experiment to determine the volume of a mole of gas at standard temperature
and pressure.
Procedure
The pictures below will help you follow the discussion of the procedure.
Fig 1 (left)
The gas measuring tube apparatus during the
experiment.
Fig 2 (right)
Equalizing the pressure inside the tube and in
room.
the
Procedure Suggestions:
1. Make a water bath by filling a 1000-mL beaker about ¾ full with tap water.
2. Obtain a strip of magnesium ribbon. Measure the length of the ribbon to the nearest 0.01 cm.
3. Measure out about 3 mL of 6 M hydrochloric acid in a 25 mL graduated cylinder. Avoid getting
acid along the sides of the graduated cylinder.
4. Fill the remainder of the graduated cylinder with distilled water. Use a pipette to drip the water
down the sides of the cylinder to avoid mixing with the acid. The water should overfill the
cylinder top slightly to form a smooth, curved surface.
5. Place the magnesium carefully on the surface of the water in the cylinder. It should float.
Quickly cover the cylinder with a square of Parafilm. Stretch the Parafilm tight and secure it
around the graduated cylinder. Make sure that no air bubbles are trapped under the plastic wrap.
6. With a pin, poke a small hole in the plastic over the cylinder mouth. Holding the cylinder by the
base, quickly invert it in the water bath. Hold the inverted cylinder vertically with its mouth
submerged. You may support the tube with a utility clamp (Figure 1). Do not block the pinhole
at the base. (why?)
7. As the magnesium reacts with the hydrochloric acid, hydrogen gas will be produced and
collected in the cylinder. When the reaction is complete (how will you know?), allow the
temperature of the gas to adjust by submerging the cylinder as completely as possible in the
water bath for about one minute.
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U9 lab – molar vol 2013
CLASS SET
DO NOT WRITE ON!!!
8. To read the volume of gas in the cylinder, lift the cylinder vertically until the liquid level inside
the cylinder matches the level of water in the water bath. Placing a piece of dark paper behind
the beaker/cylinder may help in making the measurement.
9. Use the gas pressure sensor to determine the atmospheric pressure in the laboratory. Record the
temperature of the room/water bath (assuming you used tap/room temperature water).
10. The liquid in the water bath and the cylinder can be disposed of in the waste beaker.
11. Compare class results so that multiple trials can be examined.
Sample Data Table:
Record data in an appropriate table in your lab notebook. Include elements of a good data table.
Mass of 1.00 m of magnesium ribbon
___ g/m
Length of magnesium ribbon used
_________ cm
Volume of gas collected
___ mL
Room temperature
___ K
Room pressure (read gas pressure sensor)
Vapor pressure of water
(see chart next to sensor)
__ mm Hg
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U9 lab – molar vol 2013
Name
Date
Pd
Unit 9 Molar Volume Post Lab
Data Analysis
Perform the following data analysis and calculations in your lab notebooks. Remember this is a left
side item!
1. The hydrogen gas collected also contains some water vapor. The pressure of this mixture of gases is
equal to the room pressure. Find the partial pressure of just the H2 gas.
2. You collected H2 gas at room temperature and at the pressure you found in #1. Determine what the
volume of hydrogen gas would be at STP.
3. Determine the mass, then the moles of Mg used.
4. Write a balanced equation to describe the reaction between the Mg and HCl. Using your equation
and #3, determine the number of moles of H2 gas produced in your sample.
5. Determine the value of the ratio:
volume H 2
. Be sure to use appropriate sig fig’s. Describe the
moles H 2
meaning of this ratio.
6. Predict the volume of a mole of another gas, say N2 or CO2, at STP. Justify your prediction.
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U9 lab – molar vol 2013
Lab Extension: Molar Volume from Gas Density
Molar volume can also be determined from measured gas densities. Consider the table below to answer
the questions that follow.
Table 1: The density of various gases at standard temperature and pressure:
Gas:
Formula
Ammonia
Density (g/L)
NH3
0.769
Ar
1.7837
Carbon Dioxide
CO2
1.977
Chlorine
Cl2
2.994
Fluorine
F2
1.695
Helium
He
0.1785
Hydrogen
H2
0.0899
Hydrogen Chloride
HCl
1.638
Krypton
Kr
3.749
Methane
CH4
0.717
Neon
Ne
0.8999
Nitrogen
N2
1.2506
Oxygen
O2
1.4290
Radon
Rn
9.73
Xenon
Xe
5.894
Argon
Extension Questions:
1. Test your prediction from data analysis question #6: using molar mass, convert the density to
moles/Liter for 2 or 3 of the gases in the table:
2. Now, express these ratios in terms of L/mol.
3. What can you conclude about the ratio of volume and moles for different gases? What
significance does this have?
4. An “ideal gas” is said to perfectly follow all assumptions of Kinetic Molecular theory. The
accepted value for the molar volume of an “ideal” gas is 22.414 L/mol.
a) Determine the % error of your molar volume of hydrogen gas from your lab.
b) Discuss why your value of hydrogen gas and the values of other real gases might deviate
from this “ideal” molar volume.
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U9 lab – molar vol 2013