Name
Period
Date
Pre-AP Chemistry
Lab - Intermolecular Attractions
In this experiment, temperature probes are placed in various liquids. Evaporation occurs when the probe is removed from the liquid’s container.
This evaporation is an endothermic process that results in a temperature decrease. The magnitude of a temperature decrease is related to the
strength of intermolecular forces of attraction. In this experiment, you will study temperature changes caused by the evaporation of several
liquids and relate the temperature changes to the strength of intermolecular forces of attraction. The attractive force between molecules is
based on polarity. A molecule which is polar has a “dipole” (+ and – parts). The bigger the dipole, the stronger the force between molecules.
• Hydrogen bonds=A special case of a polar molecule. These are really strong in a molecule with an
–OH part. An –OH at one end creates a more exposed (“sticky”) part than an –OH in the middle of
the molecule.
• Dipole Attraction=Any time there are two different types of atoms in a molecule, a small dipole is
created. The bigger the difference in electronegativity, the larger the dipole. Again, dipoles near
one end of a chain are exposed and are stickier than ones in the middle.
• Induced Dipole = The weakest type of polar attraction. When any two molecules pass each other,
the protons of one molecule pull on the electrons of the other. The more electrons there are, the larger
this temporary dipole is. Basically, big molecules are stickier than small ones just because there are
more electrons to get attracted to the other protons.
Group 3
Group 2
Group 1
Data
As you measure the temperature of an evaporating liquid, fill in the data table. Determine the molecular weight and structural formula of
each molecule. A few examples have been done for you.
Compound
Formula
methanol
CH3OH
ethanol
C2H5OH
1-propanol
C3H7OH
1-butanol
C4H9OH
acetone
C3H6O
1-propanol
C3H7OH
2-propanol
C3H7OH
pentane
C5H12
1-butanol
C4H9OH
2-butanol
C4H9OH
Water
H2O
Lab: Intermolecular Attractions
Structural Formula
Molecular
Weight, u.
Large, medium,
small or zero
dipole?
Initial
Temp;
Tinitial, K
Final Temp;
Tfinal, K
Change in
Temp =
Tfinal –Tinitial
K
18.02
1
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Analysis & Interpretation
1.
Why does the temperature drop as the liquid evaporates?
2.
___________________ Does a large temperature drop correspond to strong or weak intermolecular forces? Explain.
3.
(a) Based on your data
and observations, rank
the compounds from
weakest to strongest
intermolecular forces.
Group 1
Group 2
Group 3
(b) What type(s) of
intermolecular force
play(s) the biggest role
within this group?
(c) What makes the
molecule with the
strongest force
different from the
others?
4.
___________________ Which compound (from this lab) has the strongest intermolecular forces? What observation supports this? Why
does this compound have the strongest intermolecular forces?
5.
___________________ Which of these substances would have the highest vapor pressure? How can you tell from your data?
6.
___________________ Which of these substances would have the highest boiling point? Explain how you know.
Lab: Intermolecular Attractions
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Lab Instructions: Intermolecular Attractions
PROCEDURE
1.
Wear goggles! The compounds used in this experiment are flammable and poisonous. Avoid inhaling their vapors. Avoid contacting them
with your skin or clothing. Be sure there are no open flames in the lab during this experiment. Notify your teacher immediately if an
accident occurs.
2.
A temperature probe should be plugged into in CH-1
3.
Wrap the temperature probe with a square piece of filter paper secured by small rubber bands as shown. Roll the filter paper around the
probe tip in the shape of a cylinder. The paper should be even with the probe end.
4.
Obtain a vial with one of the samples. Clamp the vial to hold the it steady.
5.
After the probe has been in the liquid for at least 45 seconds, press Start
seconds to establish the initial temperature of each liquid.
6.
Now remove the probe from the liquid and tape it so the probe tip extends 5 cm over the edge of the table top as shown.
7.
After the data collection stops, find the change in temperature. Use the menu Analyze > Examine and hover over the temperature data to
find the final temperature, T2, and the initial temperature, T1. Record these in your data table.
8.
Subtract the initial temperature from the final temperature to determine ∆T, the temperature change during evaporation. (∆T=T2–T1)
9.
Throw the filter paper into the garbage and prepare a new piece for the next trial.
to begin data collection. Monitor the temperature for 15
10. Repeat this process with all the other samples.
• If the compound appears twice in the table, use your previous data (don’t repeat the same liquid again).
• Pressing the start button
Lab: Intermolecular Attractions
clears the old data. You don’t need a new file.
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Group 3
Group 2
Group 1
Table with strutures
Compound
Formula
methanol
CH4OH
ethanol
C2H5OH
1-propanol
C3H7OH
1-butanol
C4H9OH
acetone
C3H6O
1-propanol
C3H7OH
2-propanol
C3H7OH
pentane
C5H12
1-butanol
C4H9OH
2-butanol
C4H9OH
Water
H2O
Lab: Intermolecular Attractions
Structural Formula
Molecular Weight
(mass of one
mole)
4
Polar, mostly
polar,
somewhat
polar or nonpolar
Initial
Temp;
Tinitial
Final
Temp;
Tfinal
Change in
Temp =
Tfinal–Tinitial
2/12/15