Friday, February 25, 2011

Intermolecular Lab Review

        In this blog I'll be giving my review from the Intermolecular Lab that my chemistry class has been preforming these past few days. The first day we did a simple Pre-Lab. In this preparation lab we were given a list of all of the substances that we would be working with and their formula. With this information we created a structural formula for each one. We also found each of these substances molecular weight (graphs x-axis) and whether or not it had a hydrogen bond or not. The next day when we came to class, we did the first part of the lab which dealt with ethanol and methanol. For each, we had a test tube of the substance (compared 2 at a time) and a probe wrapped with filter paper at the tip held on by rubber bands (separate for each substance). We repeated the process (for the other substances) of dipping the probes into each substance for 15 seconds and then pulling them out simultaneously as we watched the computers, which the probes were hooked to, to see which substance temperature would decrease the most (graphs y-axis). Our data chart read this informations:

SUBSTANCE:               INTIAL TEMP:           LOWEST TEMP:        CHANGE IN TEMP:
ethanol                                 21.3 C                                8.4 C                           13.4 C
methanol                              23.7 C                                1.7 C                           22.0 C
propanol                              21.8 C                               14.5 C                             7.3 C
butanol                                22.7 C                               18.1 C                              3.6 C
pentane                                21.9 C                                 -.9 C                            21.0 C
hexane                                 21.4 C                                4.2 C                            17.7 C

Between each of these testings we made predictions of each substances temperature change. We were never right on, but several of them came pretty close. We based our predictions off the previous experiment testings of ethanol and methanol. We figured that the bigger the mass the less the temperature changes, which was correct, but as I said, none of our numbers were right on.
     Finally, after we had collected all of our data, we did a Post-Lab where we processed our results. We used our data from the pre-lab and from our data table (shown above) to make a graph of the substances to show how molecular weight affects the change in temperature. As we had predicted, the larger the mass of the substance the less it changed in temperature and that was proven by this graph of our data (pentane and hexane not included in this explanation).

        To explain this graph and this whole lab a bit more and wrap up, I would like to tie all of this together back with the term intermolecular forces. As I stated before, we concluded that the larger the mass a molecule has the less the molecule changed in temperature and this is because of intermolecular forces. Here you can picture something really sticky vs. something easy to break, a rice crispy vs. a dry cookie. This relates to intermolecular forces because the larger the substance, the more complex it is, meaning the more atoms it has to hold it together, therefore being a lot like the rice crispy and more resistant to fall apart. A substance more like methanol however, tends to be a lot more like the dry cookie. Methanol's structural formula contains one carbon and a few hydrogens hanging on and connected to an oxygen and a hydrogen. This is a fine structural formula, but it isn't sticky. The bonds between these substances aren't as strong causing the substance to be much easier to just break apart, resulting in evaporation taking some of the heat energy with it and larger temperature changes. As for how intermolecular forces deal with temperature change it's like this: if a molecule is larger and "stickier" then during the reaction more energy is used trying to break down the substance rather than changing its temperature and if a molecule is smaller and "less sticky" then it doesn't take the reaction long at all the break down the substance so it has more energy to work on changing the temperature.
        Overall, I liked this lab. I thought it was a fun hands on way to understand how molecular weight can change the temperature. I understand the concept that a molecular weight affects the change in temperature of a substance. For example, the lighter the substance the more its temperature will change and the heavier a substance the more likely it is for its temperature to be fairly close to its original. From this blog I would really like to achieve a 4 in communication and lab skills, because I feel I understood this well enough to share it in an easy-to-understand blog and my lab skills were EXCELENTE! :)

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