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The Effect of Intermolecular Interactions

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Gabriel Perez

on 14 February 2014

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Transcript of The Effect of Intermolecular Interactions

Academia La Milagrosa
Science Department
Science Fair

The Effect of Intermolecular Interactions within Boiling Points and Viscosity

Gabriel Perez Otero
Maribel Hiraldo

The purpose of this project was to study intermolecular forces. These forces are present in many chemical processes where molecules are involved. In this project we studied the properties of Boiling point and Viscosity
Experiment3: Viscosity of different liquids
Experiment1: Boiling point of different compounds
Experiment2: Increase in the boiling point
Materials and Metholodgy
Compounds with the strongest bond interaction will be harder to evaporate and weak bond compounds will be easier. If ions are added to water, ion-dipole interactions should form and increase the boiling point. Also if a viscous liquid is heated, it should become less viscous because the molecules of the liquid seperate.
Can we predict the way compounds such as water, alcohol and oil evaporate and explain the viscosity of water versus syrup based on the chemical structure and intermolecular interactions of the compounds?

In their book Chemistry Matter and Change, the authors define an atom as "the smallest particle of an element that retains all the properties of that element" and a molecule as "the joining of two atoms and is lower in potential energy then its constituent atoms.
The world of chemistry is based on atoms, how they form into molecules and how the molecules interact. The stronger the interactions between molecules the harder they are to seperate. Strong interactions increase the boiling point and viscosity of compounds and these properties will be studied in this project through 3 experiments.
Atom Bonds
Atoms join together in different ways. One way is by covalent bonds which are based on atoms sharing electrons. Another interaction is by ionic bonds where one atom with and extra electron transfers it to another atom. The resulting atoms are now called ions because they have an electrical charge.
Intermolecular Interactions
Atoms that join together form molecules. These molecules can interact with other molecules to form complex structures. The interaction between the molecules depends on the size of the molecules, the shape and orientation of the molecules and the electrical attraction between them. Four types of intermolecular attractions exist.
Phase Change
The physical state of an object depends on how tightly packed the molecules are. By heating or cooling the molecules you can switch the solid, liquid and gaseous forms of a compound. A compounds boiling point is the temperature at which a liquid turns into a gas as a result of heat. Certain liquids are more dense then others which is describes as viscosity and depends on how tightly packed liquid molecules are.
Tin Foil
Isopropyl (Alcohol swabs)
Tin cans
1.Boiling point of different compounds
2.Increase in the boiling point
3.Viscosity of different liquids
1.Boiling point of different compounds:
a. Choose Different compounds for the experiment, for this experiment water, oil and isopropyl (alcohol) were used.
b. Heat a stove to maximum temperature.
c. For each compound pour drops on to the stove and take the time for it to boil.
d. Finally compare each compound.
2.Increase in the boiling point:
a. Heat a stove to maximum temperature.
b. Place two tin cans on the stove, one with water and the other with water + salt.
c. While the water is heating measure the temperature at different time points with a thermometer until the water starts to boil.
d. When the water starts to boil, remove the materials.
e. Compare the boiling points using the temperatures measured at the different time points
3. Viscosity of different liquids:
a. Gather the liquids to be used in the experiment. In this experiment water (to compare with) and syrup were used.
b. Pour each liquid in a cup and measure the time.
c. Heat the more viscous liquid (syrup) in a tin can at maximum temperature for 5 minutes.
d. Pour the heated liquid into the cup and measure the time.
e. Compare the times and determine if heating the liquid made a difference.

For the first experiment the boiling point for different compounds was compared. It was determined that the alcohol boiled first because it has the weakest intermolecular forces, followed by drinking water, tap water and oil which has the strongest intermolecular forces.
In the second experiment, the affect of adding salt to water to the boiling point was studied. A graph was made and showed that by adding salt, the boiling point of water increases. This is because ions in salt interact with water molecules to form ion-dipole interactions which are stronger and harder to seperate than the hydrogen bonding interactions in water alone.
In the third experiment the viscosity of compounds was tested and how heat affected their viscosity. It was demonstrated that by heating a viscous compound like syrup, it became less viscous and poured faster into a cup. The reason behind this is that by applying heat, molecules separate. The more separate the molecules are, the more liquid-like the compound is.
It was determined that the stronger the intermolecular forces are the higher their bioling point and viscosity are.
The stronger the interactions the slower they evaporated and the weaker the interactions the faster they evaporated.
If you add salt to water, the ions in salt will interact with water molecules and increase the boiling point.
Heating a liquid will separate molecules and decrease the viscosity of a liquid.
These concepts play key roles in chemistry.
It is important to know about intermolecular forces because they determine how molecules interact to form complex strucutures and reactions. Without these interactions the complex structures of organisms could not be formed. With the general concepts of these forces, you can predict the behavior of molecules which is important knowledge in chemical industries or laboratories. Also with the knowledge of these forces we can choose certain compounds to use in appropriate scientific experiments.
If I were to repeat these experiments, I would increase the number of compounds to use and compare. Another property that could be studied is the melting point (for solids) and freezing point (for liquids) of certain compounds.
Chemistry A Molecular Approach. Nivaldo J. Tro, 2008, Pearson Education, Inc.

Chemistry Matter And Change. Glencoe Science, 2008, McGraw-Hill Componies, Inc.

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