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Experiment 1
19 January 2017
Intermolecular Forces
Today: two categories of compounds
• 1. Alkanes
– Straight chain of carbons
and hydrogens
• London dispersion
n-pentane (line structure)
forces only
n-pentane (stick structure) n-pentane space filling
Today: two categories of compounds
• 1. Alkanes
– Straight chain of carbons and
hydrogens
• London dispersion forces
• 2. Alcohols
– Have –OH group at the end
• Hydrogen bonding
(dominates) and some
dipole-dipole
• London dispersion
hexane
n-pentanol
Evaporative Cooling
• Evaporation requires breaking the
intermolecular forces holding the liquid
together
• This takes energy! (Endothermic)
• Temperature is a measure of energy…so when
energy goes into making liquid evaporate, the
surroundings cool down
– This is one of the functions of perspiration
Probe
removed
from liquid
Min temp
reached
What does the data imply?
• Large DT  fast evaporation
• Fast evaporation  a lot of molecules have
sufficient kinetic energy to escape the liquid
 high Pvap
• high Pvap weak intermolecular forces
Details for today
• Write an introduction
• You do not have to copy the procedure – merely
refer to it. It is necessary to completely describe
any modifications and changes.
• Group A or Group B. Each pair will analyze three
solvents – other pair at your station will do the
other three solvents.
• Submit on-line data before you leave today.
• You will use CLASS data to compare your results
with the others in your group. This information
will be available at the Chm 206 website at 4 pm
today.
• Lab reports due tomorrow at the start of class.
More details for today
• Organic solvents are often toxic
– Immediately cap and return bottles as soon as
you’ve started data collection
• Disposal
– Used filter paper should go in a beaker in the
hood (right after you’re done with it)
Laptops
• You will need LoggerPro
• With PC laptops in particular, plug in
temperature probe before starting LoggerPro
• Take screen shots of your three experiments.
Crop them and paste them into a Word
document, sized to fit on one page. This is
part of your lab report due tomorrow.
• Send a copy of the Word document to your
lab partner as an e-mail attachment
Your Lab Report
1. Cover sheet with the TA’s initials on it
2. Lab notebook pages (carbons) – remove the left left
strip of spiral holes if necessary
3. Attached graphs (I do not accept electronic versions
of the graphs – they must be physically attached)
4. Stapled (I will have a stapler available prior to start
of class)
5. Late after the start of class (even if it is your lab
partner’s fault).
You can download this presentation at the Chm 206 website.