Friday, February 19, 2010

Lewis Structures and Molecular Shape

Shapes and Lewis Structures of Molecules

Background Information:

Everything is made out of different kinds of molecules. These molecules are made out of different combinations of atoms that are brought together by different kinds of bonds. We did this lab to better understand how these bonds are formed and what kind of molecules are made from these different bonds. These bonds occur when the electrons of an atom share themselves with those of another.

The best way to do this is to first make a lewis structure of the molecule you are inquiring. Lewis structures are diagrams that show the bonding between different atoms of a molecule, and the lone pairs of electrons that may exist in the molecule. It can be drawn for any covalently-bonded molecule. It was named after Gilbert N. Lewis, who introduced it in his 1916 article The Atom and the Molecule.

Reasoning For Experiment:

We did this experiment to better understand the way different molecules bond to one another and the shape they attain in the process. Analyzing the structure, you are able to obtain more information about its changes in properties and the polarity of the molecule.

Materials:

Here are is a picture of what we used to make our models for this lab



Procedure:

  1. Build a model for each of the molecules listed on the data table on the back of this page.(Remember that some atoms can form multiple bonds.)
  2. Draw the three-dimensional structure of each molecule in Table 1. (make a copy of Table 1 on your own paper) Use solid lines to represent bonds in the plane of the paper, and wedged lines for bonds that point of from the plane of the paper toward the viewer.
  3. Note that the shape of each molecule in the third column of Table 1, the bond angles in column 4, whether or not they will be polar in column 5, and whether or not they exhibit resonance structure in column 6.

Results:


Here is a data table of 6 different molecules we decided to post. Included is the name of the Molecule, the Lewis Structure of it, the ball stick model, the shape, and the polarity of each. For the N2 molecule, we put in an incorrect structure in as an example. It should have a triple bond instead of a single bond. The SO3-2 Molecule was the only resonance structure included in this experiment. This means that it can have multiple ways of bonding and still result in to the same molecule and shape.


Click on Table for better clarity



Analysis Questions:

Explain how water's shape causes it to be polar.

Water is polar due to the fact that the hydrogen atoms only have their proton on the outside, where the electrons are bonded to the oxygen and the extra negative atoms of the oxygen are on the other side, making the molecule polar


Describe how water's properties would be different if the molecules were linear instead of bent.

If water was linear, there is a chance that the water would become non-polar, changing the way it reacts with other atoms and molecules.

Thursday, February 4, 2010

Paper Chromatography Lab

Paper Chromatography Lab

Chromatography Lab


Before we start, let us tell you a little bit more about what chromatography actually is and why it is used.


About Chromatography:


Chromatography is a procedure that is used to separate mixtures. This involves passing a mixture through a stationary phase, also known as a "mobile phase". As the mixture goes through the mobile phase, subtle differences in concentrations of each part of the mixture. It was first used in the mid 19th century primarily to separate plant pigments, most likely chlorophyll. It is attributed to Russian botanist Mikhail Semynovich Tsvet who used columns of calcium carbonate for seperating plant pigments during the first decade of the 20th century during his research of chlorophyll.



Reasoning for Experiment:

This experiment is to help us learn more about the bonds of different mixtures and compounds


Problem Statement:

Compare different solvents' polarity and ability to separate a mixture into its pure components.

Hypothesis:

Due to its attractive force that would allow the solution to move up the paper, we believe water will extract the solvent, moving the ink up the chromatography paper.

Materials:

Solvents - H2O (water), CH3OH (methanol), C3H7OH (propanol), and C6H14 (hexane)

Mixtures - Water-soluble overhead pens (black, red, green, blue, and yellow)


24-well plate

Chromatography paper strips (1 cm x 8 cm)

Safety materials (apron and goggles)


Procedure:
PART 1

Before you start the lab, put on safety apron and goggles to prevent injury to hazardous material. Be careful, some of the mixtures are dangerous and should be used under a fume hood. First of all, cut chromatography paper into 1 cm x 8 cm strips. Fold the strip about 1.5 cm from one end. Put a pencil line near the crease and dot black marker across the pencil line. Be sure to allow the ink to dry. Label each strip on the opposite end with a pencil. Then, fill 4 separate wells on the 24-well plate approximately half full of the following solvents.

H2O, CH3OH, C3H7OH, and C6H14. (Beware, some of these fumes can be dangerous)

Next, place the chromatography paper strips into the solvent, not allowing the marker dots to be inserted into the solvent. Last of all, record your observations as you let the solvent to wick up the paper for 1/2 hour.

PART 2

Choose the solvent that best separated the ink's pigment from PART 1 and test its ability to separate different colors. Obtain 4-5 strips of chromatography paper, depending on how many colors you have, repeating the steps for labeling and adjusting the strips. Next, fill that many separate wells of the 24-well plate with a single solvent 1/2 full. Place the strips into the solvent, not allowing the marker spots to enter the liquid. Again, allow the solvent to wick up the paper for 1/2 hour. Record observations, sketching the results as shown for water.












Results:

As you can see in the photo above, red and green ink seem to have a variety of pigments compared to blue and yellow, which consist of only its own color.


Conclusion:

After experimenting with the solvents and inks, we conclude that our hypothesis is correct. Water transferred the ink up the chromatography paper the most effectively out of all the solvents.

Listed from best to worst solvents: H2O, CH3OH, C3H7OH, and C6H14

From doing this lab, we learned about chromatography paper and its ability to reveal information about certain solvents.

Anomalies

This Experiment could have been more interesting and a learning experiment if we had a wider range of colors and chemicals to work with.