Download Evaporation and

Academic Chemistry Lab: Intermolecular Force Study
(34 points)
(page 1 of 3)
Reference: Zumdahl Chapter 10 section 1 Intermolecular Forces
Zumdahl Chapter 22 section 1 Alkanes
Zumdahl Chapter 22 section 4 Hydrocarbon Derivatives
Background:
In this investigation, 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, like viscosity and boiling temperature, related to the strength of
intermolecular forces of attraction. In this investigation, 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.
You will encounter two types of organic compounds in this investigation—alkanes and
alcohols. The two alkanes are pentane, C5H12, and hexane, C6H14. In addition to
carbon and hydrogen atoms, alcohols also contain the -OH functional group. Methanol,
CH3OH, and ethanol, C2H5OH, are two of the alcohols that we will use in this
investigation. You will examine the molecular structure of alkanes and alcohols for the
presence and relative strength of two intermolecular forces—hydrogen bonding and
dispersion forces.
Materials:
IBM compatible computer
LabPro
Logger Pro
two temperature probes
six 3cmX3cm filter paper
rubber bands, or Al wire
iron ring and stand
methanol (CH3OH): flamiable and poisionous
ethanol (C2H5OH): denatured, flammiable and poisionous
1-propanol (C3H7OH): flamiable and poisionous
1-butanol (C4H9OH): flammable and poisonous
n-pentane (C5H12): flammable and poisonous
n-hexane (C6H14): flammable and poisonous
Pre-lab exercise:
Prior to doing this investigation, complete the Pre-Lab table. The name and formula are
given for each compound. Draw a structural formula for a molecule of each compound.
Then determine the molar mass of each of the molecules. London intermolecular forces
exist between any two molecules, and the attractive force increases as the molar mass of
the molecule increases. Next, examine each molecule for the presence of hydrogen
bonding. Before hydrogen bonding can occur, a hydrogen atom must be bonded directly to
an N, O, or F atom within the molecule. Tell whether or not each molecule has hydrogenbonding capability.
Academic Chemistry Lab: Intermolecular Force Study
(34 points)
(page 2 of 3)
Procedure:
1. Plug Temperature Probe 1 into Channel 1 and Temperature Probe 2 into Channel 2 of
the LabPro interface. Connect the computer to the LabPro using the interface cable
and boot LoggerPro
2. To up the data collection time select expirment/data-collection. The mode should be
time based. Collect data for about 240seconds (4minutes). There should be about
one reading per second.
3. Wrap Probe 1 and Probe 2 with a 3cm by 3cm square pieces of filter paper and
secure with a small rubber band. You are trying to manke a paper skirt and not a
paper sock. The paper should be even with the probe end. Suspend these probes
from an iron ring so that they hang freely.
4. Find your goggles. Pour about 1cm of ethanol and 1cm 1-propanol into two separate
test tubes. Insert probe 1 in the ethanol and probe 2 in the 1-propanol. Take special
care not to confuse the two.
5. After the probes have been in the liquids for at least 30 seconds, tap
to begin
collecting temperature data. A live graph of temperature vs. time for both Probe 1 and
Probe 2 is being plotted on the handheld screen. The live readings are displayed in
the lower left corner. Monitor the temperature for 15 seconds to establish the initial
temperature of each liquid. Then simultaneously remove the probes from the liquids.
6. Data collection will stop after 4 minutes (or tap
if you want to end data collection
before 4minutes has elapsed).
7. If you are satified with your graph scroll through the data table and record the
maximum temperature, and minimum temperature for each chemical
8. Adjust your scale so all data is graphed. Title you graph and call out which chemical
is on which temperature probe. Remember the printer only does black and white.
9. Repeat Steps 4-8 using 1-butanol, n-pentane, methanol, and n-hexane. Use new filter
paper for each chemical studied.
Calculations:
1. Calculate t for each chemical studied.
2. Plot t versus molar mass using data from the four alcohols. Put molar mass on the
horizontal axis and t on the vertical axis. If the data is good a smooth relationship
should be seen here.
3. Select any best fit curve that produces a low root mean square error (RMSE).
Name: ________________________ period: _______ (34 points) (page 3 of 3)
Academic Chemistry Computer Lab: Intermolecular Force Study
Pre-lab data table: (2 points)
Substance
Formula
methanol
(an alcohol)
CH3OH
ethanol
(an alcohol)
C2H5OH
1-propanol
(an alcohol)
C3H7OH
1-butanol
(an alcohol)
C4H9OH
n-pentane
C5H12
n-hexane
C6H14
Structural Formulas
Molar Mass
(g/mole)
Hydrogen Bond
(Yes or No)
Data table: (2 points)
Substance
tmax (°C)
tmin (°C)
t (tmax–tmin) (°C)
methanol (an alcohol)
ethanol (an alcohol)
1-propanol (an alcohol)
1-butanol (an alcohol)
n-pentane
n-hexane
Questions: (2 point each)
1. Two of the liquids, n-pentane and 1-butanol, had nearly the same molar mass, but
significantly different t values. Explain the difference in t values at the atomic level.
2. Which of the alcohols studied has the strongest intermolecular forces of
attraction? ____________The weakest intermolecular forces? ________
3. Explain your answer for question two at the atomic level.
4. Which of the alkanes studied has the stronger intermolecular forces of attraction?
____________ Which has the weaker intermolecular forces? ___________
5. Explain your answer for question 4 at the atomic level.
Note: Each temp v/s time graph for the six chemicals studied. (12 points total).
The alcohol temperature change v/s molar mass graph is 8 points.
Page 3 of 3 completed. (14 points)
Remember: No credit for xerox or traced copies.