Lab Session II - Intermolecular Forces Investigation: Evaporation Rate

1. An introduction to the physical property that your group was investigating and how it is related to IMF´s.

The evaporation rate of a material is the rate at which it will vaporize, this is, change from liquid to vapor, compared to the rate of vaporization of a specific standard known material. The general reference material for evaporation rates is n-butyl acetate (commonly abbreviated BuAc).

Moreover, it is important to know that evaporation rates normally have an inverse relationship to boiling points. The higher the boiling point, the lower the rate of evaporation.

This physical property is clearly related to IMF’s. If the chemical we are studying has weak intermolecular forces, it will need very little energy to break the bonds and therefore the molecules would separate easily from each and would vaporize quicker. This chemical would have a high evaporation rate as many molecules would reach the gas phase.

However, if the substance had strong IMF’s it would require much more energy in order for the molecules to separate, vaporize and reach the gas phase, as the bonds would be very tight. Therefore, very few molecules would evaporate and they would do it slower. The substance would have a low evaporation rate.

In conclusion, strong IMF’S slow evaporation rates and weak IMF’s accelerate evaporation rates. 

2. A description of the 2 groups of chemicals including; name, structure and types of IMF present.

Group 1 – Similar Molecular Weight: All the compounds in the following table have very similar molecular masses.

Group 2 – Homologous Series: The compounds in this table have a very similar structures and vary only by the number of CH2 units in the main carbon chain.

3. A prediction (hypothesis) of the results you expect with scientific explanations.

According to the theoretical background we expect certain results. We expect a substance with stronger IMF’s to have a lower evaporation rate, because it needs more energy in order to break its molecular bonds and so, less molecules would be able to reach the gas phase and they would do it slower. Some examples of these chemicals from Groups 1 and 2 are: Butanol, Propanoic acid, Propyl acetate and Butyl acetate, as they have Hydrogen Bonding, which is the strongest type of IMF.

As to substances with weaker IMF’s (Van der Waal’s and Dipole-Dipole forces), such as Diethyl Ether, Pentane, Methyl acetate and Ethyl acetate, they should have higher evaporation rates as they need less energy to break down bonds and more particles have more facility to reach the gas phase. 

4. Suitable tables of results (title, headings, units).

Butyl Acetate

Deithyl Ether

Propyl Acetate

Ethyl Acetate

Methyl Acetate

Pentane

Butanol 

Propanoic Acid

5. To what extent do your results match what you had expected

The results that we have come up with match exactly what we were expecting. Compounds with strong intermolecular forces evaporated very little or didn’t at all.  We would say the evaporation rate of these was minimal. However, the compounds with weaker intermolecular forces did evaporate and consequently have a higher evaporation rate. We can see this perfectly in the graphs. When the curvature is bigger, the higher the evaporation rate is.

We can say we are very satisfied with the data we recorded since it looks totally coherent.

6. An evaluation explaining areas where error could have occurred and how you would improve these areas in a future investigation.

So maybe the angle in which we put the stick inside the test tube wasn’t always the same and this could have altered the results since the machine  might not have gotten enough data. A possible solution to this would be to leave the stick in the test tube somewhere without moving it and this way the machine would always be in the same position and therefore the information would have been gathered always the same way. 

Another error in the method was that we didn’t measure the temperature of the test tube. If we don’t heat or cool the test tube to reach a certain temperature we don’t know if the temperatures in the different test tubes are the same. This is an essential fact when talking about evaporation rates as depending on temperature, which gives energy to the molecules inside chemicals, bonds in the substances will be more or less able to break down, which has a direct consequence on the vaporization of its particles. If temperature is lower, a chemical with strong bonds, such as hydrogen bonds, would have a very low evaporation rate. So, if we don’t have the same temperatures in each test tube, results won’t be reliable. A possible solution for this is simply measuring the temperature of each of the test tubes with a thermometer in order to have the same at each time. If needed we must heat or cool the test tube. 

Apart from this, we could have improved our accuracy while doing the experiment. But this is our mistake and we wouldn’t have to change the method for this.

7. At least 2 references in APA format.

Pubchem.ncbi.nlm.nih.gov,. (2015). PubChem. Retrieved 25 January 2015, from

http://pubchem.ncbi.nlm.nih.gov/compound/1-butanol

BusinessDictionary.com,. (2015). What is evaporation rate? definition and meaning. Retrieved 25 January 2015, from http://www.businessdictionary.com/definition/evaporation-rate.html

Ilpi.com,. (2015). The MSDS HyperGlossary: Evaporation Rate. Retrieved 25 January 2015, from http://www.ilpi.com/msds/ref/evaporationrate.html

Socratic.org,. (2015). How do intermolecular forces affect evaporation? | Socratic. Retrieved 25 January 2015, from http://socratic.org/questions/how-do-intermolecular-forces-affect-evaporation