Evaporation and Intermolecular Attractions 10

'Twas an extremely exciting day in the lab today, because Ameera and I, the probe buddies, finally got to use a real probe!!!! It was simply monumental.

Here is our pre-lab data: Lewis dot structures, molar mass, and intermolecular attractive forces OH MY!

Here is the data we collected after using our probe to test the evaporation rates of the 5 substances above.

Calculations and Results

2.

• Methanol's temperature went down 6.3 degrees celsius during the course of the experiment. This is a large change in temperature, which means that much of the methanol evaporated in 240 seconds compared to the other substances, so methanol has a very high vapor pressure. This also means that there are comparatively not very strong bonds in methanol -- though it has London dispersion forces and dipole-dipole IMF's like every other substance tested, it only has one hydrogen bond and less molar mass than the others, so the less strong bonds did not hold onto their electrons well enough and they were released in the form of vapor.
• Ethanol only dropped 0.8 degrees C , which shows that it has stronger hydrogen bonds in comparison to methanol, that only allowed for a lesser vapor pressure and a lower amount of evaporation.
• n-Butanol had a temperature drop of 1.6 degrees C during the evaporation process, which shows that it has a higher vapor pressure than ethanol, but weaker hydrogen bonds. Our data does not make much sense in this case, because n-Butanol has a more complex Lewis Dot Structure with many more bonds and a larger molar mass than ethanol, so it should have a lower vapor pressure.
• Glycerin was the funky substance of the bunch. It actually gained 0.6 degrees C during the experiment. This demonstrates the strength of its 3 very strong hydrogen bonds in producing a very low vapor pressure and allowing the reverse process of condensation to occur. Glycerin is a very nonvolatile substance.
• Water gained 1.6 degrees C throughout the experiment. Though it has 2 strong hydrogen bonds, it also has a very small molar mass of only 18.g in comparison to the other substances so more evaporation occurred.

3. Glycerin and n-Butanol have similar molar masses with a difference of only 17.97 g. Though their molar masses are similar, n-Butanol has far more hydrogens while glycerin has more oxygens and in turn more hydrogen bonds. This greater number of hydrogen bonds allows for little to no evaporation, while the lesser number of hydrogen bonds in n-Butanol allows more a much higher vapor pressure and more evaporation.

4. The number of -OH groups in the tested substances greatly effected the ability of each substance to evaporate. As discussed previously, more -OH groups (or hydrogen bonds) caused a lower vapor pressure and less evaporation because the electrons were bound more tightly and did not float as freely as the substances with fewer hydrogen bonds. These substances saw much more evaporation and a higher vapor pressure.