4. Forces

Polarity

Polarity: We began Journey 4 of Honors Chemistry class by learning about polarity. Polarity is the distribution of electrons in a covalent compound controlled by binding energy. Polar has an unequal distribution (a-symmetric), and non-polar has an equal distribution (symmetric).

Polarity: To study the concept of polarity, we performed the following experiment. In this experiment, we learned the difference between polar and nonpolar. The materials we used were a test tube, paper towel, tweezer, bulb pipette, samples of water (H2O), hexane (C6H14), iodine (I2), and copper (II) Sulfide (CuS). In this experiment, we were instructed to add two full squirts of water (H2O) and two full squirts of hexane (C6H14) to the test tube. Then we placed a thumb over the paper that covered the test tube’s opening and inverted it a few times. We then observed. Next, we added two full squirts of blue copper (II) Sulfide (CuS) and repeated above. We then observed. Then, using tweezers, we added 1 piece of iodine (I2), observe, capped with thumb and paper, inverted several times, and then observe again. We found that the hexane (C6H14) and iodine (I2) were beside each other in the upper layer of the tube. We also found that water (H2O) and copper (II) Sulfide (CuS) mixed in the lower layer of the tube.

We concluded that hexane (C6H14) and iodine (I2) remained together because both compounds are nonpolar, which means they do not attract to anything. (There is no charge.) We also concluded that the water (H2O) and copper (II) Sulfide (CuS) mixed because they are both polar. (Opposites attract.)

Penny and Water Drops: To further study the concept of polarity, we performed a penny experiment. In this experiment, we tried to determine how many drops of water a penny can hold before the water spills off. The materials we used were a bulb pipette, water, and a penny. In this experiment, we added drops of water onto the penny, using the pipette, and counted how many the penny could hold until it spilled off. We found that the penny held several drops and actually formed a dome. We concluded that this is because the water molecules are polar and they bond with each other.

Sand: In this lab, we were given two types of sand , a green sample and a blue sample and asked to observe how each interacted with water. The materials we used were a cup, bulb pipette, spoon, water, and the colored samples of sand. For the experiment, we placed a small ball of green sand into a cup. We played with it by rolling it around and flattening it in our hands. We then added a few drops of water to the sand and observed. We found that the water mixed in with the sand. Next, we took a cup and filled the cup with blue sand to the 1/3 mark. We then added water to the 2/3 mark and stirred with a spoon. Next, we scooped out some of the sand and observed. We found that the blue sand did not appear to mic at all with the water.

We concluded that the green sand is polar, so water could mix with it. We concluded that the blue sand is non-polar, so water was repelled and would not mix.

The polar blue sand has a greater tendency to combine within itself and so does not like to bond with other compounds. It therefore repels polar compounds such as water.

intermolecular forces

Intermolecular Forces: In the final part of Journey 4, we learned about the four Intermolecular forces. Intermolecular forces are the uneven sharing of electrons. There are four intermolecular forces: London Dispersion (gas), Dipole-Dipole (liquid), Ion-Dipole (solution), and Ion-Ion (solid). Examples are shown below.

Dry erase Expo Markers: In this phase of intermolecular forces , we learned that dry erase ink was able to float off of a plate when water was added to it. The materials we used in this experiment were blue and black expo ink pens, a plate, and water. In this experiment, we used the pens to write on the plate and then added water to cover the ink on the plate. We observed and found that the blue ink came off of the plate and floated in the water.

My hypothesis for this is the following. The ink (and the resin) is non-polar, so it repels water, and the compound within the ink remains bonded to each other, so it sticks together in the water.

Bubbles: During this portion of the class, we experimented with bubbles. We mixed water, detergent, and glycerin. The bubble that is formed is made up of soap molecules with a water molecule in between each. The water molecules then spread out and lower the surface tension. The lowering of the surface tension is what allows the bubbles to form. Glycerin is added to bubble solutions to help the bubbles last longer and be stronger. Glycerin does this by making the bonds within the solution stronger so that the bubbles can stretch more.

Glycerin

Water

Detergent

In this solution, the glycerin molecules formed weak bonds with the water molecules. By doing this, it made it more difficult for the water molecules who are bonded to each other, to leave the surface, thus slowing down the evaporation process.

Below are examples of the four intermolecular forces - London Dispersion (gas), Dipole-Dipole (liquid), Ion-Ion (solid), and Ion-Dipole (solution).

reflection

Overall, I really enjoyed this portion of honors chemistry class. I find chemistry to be extremely interesting. I learned all new concepts and a lot of information during Journey 4. It was short, but full. I feel that Ramsey is an amazing teacher, and I grasped all that he taught. When I am initially unsure about any concept, he easily clarifies it for me.

As the last part of this phase of our class concluded, I prepared for the test. I did this by reviewing class notes, my labs, and the homework. I felt that I was prepared for the test.

Overall, I learned a lot of information and I love everything about the class to this date.

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