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Intermolecular Forces

My experiment for sophomore chemistry on the presence of intermolecular forces in alcohols and alkanes, and how they affect the rate of temperature change.

Megan Luanne

on 13 January 2014

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Transcript of Intermolecular Forces

Inter-Molecular Forces:
Alkanes v.s. Alcohols
What are alcohols and alkanes?
What are the similarities and differences between alkanes and alcohols?
What is an inter-molecular force [IMF]?
What are the types of IMF?
What determines the IMF of a molecule?
What kind of IMF do alcohols and alkanes possess?
How does the IMF of a molecule affect the rate and amount at which the temperature changes?
What are alcohols and alkanes?
Alcohol is a compound.
Alcohol consists only of C, H, and O.
The structure consists of a chain of C-atoms with H-atoms branched off and an O-H group.
There are different types of alcohols.
Alcohols are grouped based on how the O-H group is positioned in the carbon chain.
The groupings are known as primary, secondary, and tertiary.
Alcohol is water soluble.
Alcohol does not conduct electricity.
Alcohols are polar.
Alkanes are compounds.
Alkanes consist only of C and H.
There are different types of alkanes.
Alkanes are grouped based on their structure.
Their groupings are known as linear, branched, and cyclic.
An alkane is essentially an alcohol with a single H-atom rather than an O-H group attached to the carbon chain.
Alkanes are not water soluble.
Alkanes do not conduct electricity.
Alkanes are nonpolar.
Ethanol Structure:
Hexane Structure:
What is an Inter-Molecular Force [IMF]?
IMF are the forces of attraction or repulsion that occur between two particles.
Types of IMF:
The attraction between H and an extremely electronegative atom (N, O, F, e.t.c.).
The attraction between the positive and negative ends of polar molecules.
London Dispersion:
The attraction between two nonpolar molecules caused by a temporary shift in the electron cloud.
IMF in Alcohols:
IMF in Alkanes:
London Dispersion:
The O-H group in the alcohol creates H-bonding.
London Dispersion:
Because alcohol molecules are polar, they are able to bond to other alcohol molecules.
London Dispersion happens between all molecules due to electron movement.
Because alkane molecules are nonpolar, the only force between them is the London Dispersion Force.
What kind of IMF do alcohols and alkanes possess?
The Experiment:
How do the different types of IMF present in alkanes and alcohols affect the amount and rate of temperature change when cooling?
I predicted that the alkane (hexane) would get colder and cool more quickly than the alcohol (ethanol) because the hexane does not have as strong of an IMF as the alcohol, therefore it will be able to cool off more rapidly and reach a lower final temperature.
Independent Variable:
Dependent Variable:
In the experiment, I used a temperature probe hooked up to a data-collection interface to determine the amount and rate at which ethanol and hexane cool when placed in a room temperature environment. I wrapped a strip of paper towel secured with rubber band around the probe to protect it, then dipped it in the ethanol. The interface recorded the data for 30 seconds with the probe in the liquid, and for 200 seconds with the probe out of the liquid (taped to a countertop). I later repeated the experiment with hexane.
As soon as I took the probe out of the liquid and attached it to the table, the hexane cooled at a much quicker rate than the ethanol. The hexane started at 25.8°C and fell to 9°C within 180 seconds. The ethanol started at 21.8°C and fell to 11.9°C within 180 seconds. The hexane had a lower final temperature and cooled faster than the ethanol, even though it started out 4° higher.
In conclusion of the experiment, I learned that hexane (an alkane) will cool more and more rapidly when left at room temperature than ethanol (an alcohol) will. This conclusion supports my hypothesis. I think that the hexane was able to reach a lower final temperature than the ethanol when left to cool off because the only intermolecular force hexane has is the London Dispersion Force, which is the weakest of all the IMFs, while ethanol has all 3 types of IMF (Hydrogen Bonds, London Dispersion, and Dipole-Dipole. This means the ethanol has stronger molecular bonds, making the bonds harder to detach and therefore it takes more time and energy for ethanol to cool off.
While some mistakes were made, this experiment still had satisfactory results, although there are some things that I could change. If I were to repeat the experiment, I would use different alkanes and alcohols to see if my hypothesis was still true- that alkanes will always cool faster than alcohols because their bonds aren't as strong. It would also be a good idea to design other experiments that test the IMF strength in relation to temperature, perhaps working with boiling and freezing points. The biggest mistake I made was recording the first 30 seconds while the probe was in the liquid for hexane, which I didn't really need to do and it messed up my table and graph a little bit. I could also fix this if I were to repeat the experiment.
This experiment is important to chemistry and to everyday life because it's a comparison of two very important compounds- alkanes and alcohols. We come into contact with alkanes and alcohols more than we realize. Alcohols are in fuels, alcoholic drinks, cosmetic products, cleaning solutions, solvents, and various chemicals. Alkanes are in paints, plastics, medicines, detergents, fuels, chemicals, and even in some foods. It's important to understand the basics of alkanes and alcohols if you are going to use them or their products, especially in relation to temperature, so that you can be safe. Alkanes and alcohols are extremely important to organic chemistry and other branches of science, but they are not exclusive to it. It's always important to understand what kinds of chemicals you're dealing with.
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