October 10, 2013
Experiment 5 - Cooling Curve of an Unknown Substance

In this lab, using the computer, we were able to form a line graph showing the decrease of temperature as the substance changed from a solid to a liquid. The cooling curve from the computer showed us what the experimental Melting/Freezing point was, which was 65.2˚C. By using the Known Melting/Freezing Points table, I determined the substance was Palmitic Acid, with an actual Melting/Freezing point at about 62˚C. The percent error between my experimental Melting/Freezing point and the actual Melting/Freezing point was 5.16%.

One reason why there could have been error between the experimental Melting/Freezing point and the actual Melting/Freezing point of my substance, could have to do with the substance inside of the beaker being impure. If the substance inside of the beaker was impure, like maybe there was dirt inside of the substance, the melting point of the substance that was impure would be lower than the melting point of the substance that was, in fact, pure.

Another example of how my experimental Melting/Freezing point differed from the actual Melting/Freezing point of the substance inside of the container, could have to do with the container itself, and how they could vary from my experiment and from the actual experiment. The size of the container that we used for the experiment inside of class, could have had a larger face on the bottom of the container than the container that was used to measure the substances inside of the table would have been inside of. If the surface area of the container that I was using inside of this lab was larger than the surface area of the container used to get the ‘actual’ degrees Celsius of the substances inside of the table in the lab, then the substance inside of my container, the one with the larger surface area, would have boiled faster, and would have also cooled faster than the substance inside of the smaller surface area container. I broke it down this way, if