Vapor pressure and intermolecular forces

INTRODUCTION

Through this experiment we are going to apply the knowledge already acquired of the different Gas Laws, and how the different boiling points depend upon the intermolecular forces between the atoms of different molecules. To perform the experiment, we will be using new materials to incorporate new and different methods, such as a computer program to calculate the changes in pressure when temperature is changed, the Schlenk tube.

Finally, we are going to complete all the tasks proposed and compare the different results obtained with other groups to learn more about other substances pressure when temperature is changed and what intermolecular forces are upon them.

OBJECTIVES

1.To improve practical skills, such as the use of the Schlenk tube, pressure sensors and the vacuum line.

2.To investigate the structure and properties of one particular chemical.

3.To investigate the effect of temperature on vapour pressure.

4.To compare results with other groups (with other chemicals) and relate them to “intermolecular forces”.

VIDEOS AND PHOTOS OF PROPYL ACETATE

GRAPH, CONCLUSION AND SCIENTIFIC EXPLANATION

The relationship between pressure and temperature of propyl acetate;
The red line is at vacuum
The blue line is at 0 degrees

The purple line is at 15 degrees
The yellow line is at 25 degrees
The green line is at 40 degrees

Conclusion;

As we can observe on the graph there are many different results, due to the different temperatures observed. Usually the lowest temperatures have the lowest pressures, while the highest temperatures have the highest pressure, due to Gay-Lussac law. As we can observe on the graph this statement is concluded as each line (from red to green), goes from the lowest to the highest temperature and also its pressure.

Scientific explanation;

As stated in Gay Lussac's law, as temperature increases, pressure increases, as they are directly proportional;

This is due to that every time that temperature increases, particles inside the container have more energy, so they hit harder and more often the walls of the container by increasing the pressure inside it.

TABLE OF RESULTS AND EXPLANATION

All of these molecules have Van der Waals forces and permanent dipole-dipole forces (except of pentane that only has Van der Waals force between its atoms), but only 2-Propanol has a hydrogen bond, that it is why it has one of the most higher boling points. The boiling points of each molecule depend on the composition of each molecule, as depending on the amount of atoms which are forming them, (due to the amount of electrons in each chemical), specially the amount of oxygens that the molecule has, the forces between them will be stronger or weaker, and due to this it will be needed more or less energy to break the bond between them and convert the chemical into a gas. The stronger or weaker forces will be performed by an increase on the number of electrons in each chemical, forming all the molecule, so the atoms which are larger (have more electrons), will have stronger intermolecular forces than the atoms with less electrons. The molecules with the highest boiling points are Butyl and Propyl Acetate, as they have the highest number of electrons due to that it is formed by two oxygens. The third molecule with the highest boiling point is 2-Propanol, as it is formed by a hydrogen bond, which is the strongest intermolecular force of all the three mentioned before. After these two molecules, the boiling point of the other chemicals depend upon the different elements forming them, while the ones which are bigger (formed by more electrons), which have stronger intermolecular forces, so they would have higher boiling points. The molecules with the lowest boling points are Diethyl  Ether and Pentane as they are formed by the lowest amount of atoms and due to this the lower amount of electrons. 

REFERENCES

Ausetute.com.au. (2014). Chemistry tutorial : gay-lussac's law of combining gas volumes. [online] Retrieved from: http://www.ausetute.com.au/gaylusac.html [Accessed: 9 Mar 2014].

Helmenstine, T. (2014). What is the formula for gay-lussac’s law?. [online] Retrieved from: http://chemistry.about.com/od/chemistryfaqs/f/What-Is-The-Formula-For-Gay-Lussacs-Law.htm [Accessed: 9 Mar 2014].

Chemed.chem.purdue.edu. (2014). Intermolecular forces. [online] Retrieved from: http://chemed.chem.purdue.edu/genchem/topicreview/bp/intermol/intermol.html [Accessed: 9 Mar 2014].