Lab 1 Evaporation Rate

Lab 1 Evaporation rate Chem Original Hypothesis 6-25: From experience I have noticed that lighter fluid evaporates faster than water, and acetone also evaporates faster than water. It seems as though the larger the mass of the molecule the faster it will evaporate. Revised hypothesis 6-26: Molecules with stronger intermolecular bonds will evaporate at a slower rate than molecules with weaker intermolecular bonds. Prediction: The fastest evaporating liquid will be the pentane, because it has no dipole to dipole attraction and will only have London forces to overcome. The next fastest to evaporate will be the cyclohexane as it will have more places where London forces can occur and will lag just behind the pentane. Third fastest will be the acetone. Acetone has one permanent dipole to attract the other dipoles resulting in a greater holding it in a liquid state. The slowest evaporating liquid will be the water. Water ‘s hydrogen bonding, being the strongest type of intermolecular force, will be the hardest to overcome to escape into the gas state and will result in the longest time. Conclusion 1) The 3 types of IMF’s that occur in a liquid are all electrical nature. The London forces occur in all molecules and are caused by moving electrons causing temporary dipoles in the molecule. Dipole- dipole forces are when a permanent dipole is created within a molecule due to the unequal sharing of electrons between atoms in the molecule. Hydrogen bonds are dipole- dipole bonds between hydrogen and fluorine, oxygen, or nitrogen. Because of the large difference between the electronegativity of hydrogen and the other 3 atoms, the hydrogen bond makes the strongest intermolecular bond. The permanent nature of a dipole- dipole bond gives that bond less strength than the hydrogen bond, but more than any one London bond. Our hypothesis was generally supported by the evaporation rate data. The one surprise was that the acetane evaporated at a faster rate than cyclohexane. The reason for this non-agreement with our hypothesis was that the London forces cumulative effect was not thought to become significant.. It seems that as a molecule gets larger its London forces get larger. Cyclohexane having one more carbon atom than pentane added enough London force to make it evaporate slower than the acetane even though it had a permenant dipole- dipole bond. 2) Molar mass seems to have an effect on evaporation rates in that the larger a molecule gets or grows from a base chemical formula, its evaporation rate will get slower. The more atoms added to a molecule, the more places London forces can occur, and as a result the greater the force will become holding the substance in a liquid state. This is evident in the increases evaporation rate of cyclohexane compared to pentane. 3) It is hard to ascertain sources of error when the data set used in this lab was performed by someone else, with no knowledge of the procedures or details of the actual experiment. One of the extensions that I was attempting to do within our group was to try and quantify a tipping point for when a molecule would get large enough that London forces would overcome dipole- dipole forces. The data set was not quite large enough to do that. 4) I learned that London forces are not as weak or trivial as I once thought. Seeing how intermolecular forces act give me better insight on how to explain phase change to my students. I feel my understanding of intermolecular is much stronger now, and I feel I am better equipped to tackle problems from a different perspective. In the past I have regarded intermolecular forces to be trivial, but after this lab I know feel their importance.