11.22.10

Announcements:

1. Lab test tomorrow

2. Quizzes on Monday and Tuesday after break

3. Unit test on Wednesday (12/01)

Homework: none.

Today, we did a lab for most of the time, and then we took a quiz with our lab group. There were two parts to our lab: Part 1 - Solubility and Part 2 - Volatility and Surface Tension.

In part one, we were given six liquids. The six liquids were hexane, ethanol, pentanol, methanol, butanol and acetone. We put each one in their own test tube, and put a few drops of water down the side of each test tube. We had to determine if the liquid would mix immediately with the water and if they stayed mix after shaking the test tube. We also recorded down our observations.

After filling out the table, we answered two questions about this part of the lab. The first question was why doesn't hexane mix in either step 3 or step 5? In step 3, we recorded whether the two liquids mixed immediately. In step 5, we recorded whether the liquids stayed mix after they had been shaken. The hexane did not mix with the water in either steps. The reason for this is because water is polar, and hexane is nonpolar. Previously, we learned that "like dissolves like", and "unlike stays separate". Therefore, because water is polar and hexane is nonpolar, the two liquids did not mix.

The second question that was answered was to explain the difference in our results for ethanol and pentanol. We also had to answer which mixed more easily, ethanol or methanol.

We had several differences in our results for ethanol and pentanol. Both did not mix immediately. After shaking, the ethanol mixed with the water where as the pentanol did not completely mix with the water. We observed that after mixing, the ethanol was clear and kind of yellow, while the pentanol was white and hazy. The methanol also mixed more easily with water because the methanol is more polar than the ethanol.

In the second part of the lab, we had to measure how much each liquid spread out and how fast each liquid evaporated. We put a drop of each of the six liquids on the table. We ranked them in order of 1 to 7 with 1 being "spreads out the most" and "evaporates the quickest", and 7 being "spreadas out the least" and "evaporates the slowest". We learned that there was correlation between whether a liquid was polar or nonpolar, how much each liquid spread out and how fast each liquid evaporated. We answered three questions related to the second part of this lab.

For the first question, we had to explain how the amount a liquid spreads out is related to the polariy of that subance. From observing each of the liquids spread out and evaporate, we recorded data which helped us find the correlations. We found that the more polar a substance is, the less it spread out. For example, water is very polar, and it spread out the least. We ranked it number 7. On the other hand, hexane is very nonpolar, and it spread out the most. We ranked it number 1.

The second question asked us to explain how the rate of evaporation is related to the polarity of that substance. We found that the less polar a substance is, the faster it evaporates. For example, water is very polar, and it took the most time for it to evaporate. But hexane is very nonpolar, and it evaporated the quickest.

Our third question was to list other factors (other than polarity) that might influence the rate of evaporation. I think an important one is temperature. If we spill water, and it's not very humid or humid outside, it takes a lot longer for the water to evaporate than if it's hot and humid. So I think that the temperature plays an important role in how long it takes substances to evaporate.

After we finished our lab, we took a short quiz together with our lab group on things that we have learned recently. Tomorrow, Mr. Paek will try to find the "weakest link" in each group, and ask that person to explain how we got our answers.

Tuesday 9.14.10

Today, our class was shortened by 10 minutes because of the Fall Sports Assembly. We learned about a new topic, atoms, and were given four worksheets to tape in our composition notebook. We learned several new terms which relate to atoms, and were crucial in helping us do the problems on the worksheets. The terms are the following:

Atom: Most basic unit of matter (example: one atom of zinc)

Molecule: Group of atoms held together by a chemical bond

Element: Made up of a single type of atom (example: two atoms of zinc)

Compound: Molecule made up of more than one type of atom. If something is a compound, it is always a molecule.

Pure Substance: Made up of one type only

Mixture: Mixture of two types

It wasn't specified what these "types" are.

On the worksheets, we did numbers #1-9. Number 1 was defining the above terms. For number 2, we were given atomic level diagrams, and we were told to identify each as being either an element or a compound, and consisting of either atoms or molecules. For number 3, we had to answer the question: Can a substance that is a compound ever be made of individual atoms and not molecules? Explain. The answer was No, because compounds are always made up of molecules. For number 4, we had to answer the question: Can a substance that is an element ever be made of molecules and not individuals atoms? Explain. The answer was Yes, because an element can have two of the same atoms connected together.

For numbers 6 and 7, we were given a key to use. The key was three circles which were shaded differently. An unshaded circle was H, a striped circle was O and a shaded circle was C. For number 6, we had to write the formula for each of the following atomic level pictures. We learned that if two of the same atoms were bonded together, then the "2" was subscripted , not written in front of the letter. For example, two chemically bonded Hs would be "H₂" , while two separate H atoms would be "2H".

For number 7, we were given the following formulas, and we had to draw a picture to match them. We used the same key that we used for number 6. For number 8, we were given pictures, and we had to write the formula and a description to match the picture. It's the opposite of what we had to do in number 7, but we also had to write a description. The description is basically a list of terms that appeared in the picture. The terms that we could use were atom, molecule, element, compound, pure substance and mixture.


The last page has numbers 9 through 13, but we were only told to go up to number 9. In number 6, we were given a formula, and had to draw a matching picture. In number 7, we were given a sample, and had to write the formula and description. Now, in number 9, we're given a formula, and have to draw a matching picture and description.
Homework: 5 webassigns due Monday the 20th.
You can get to the Webassigns by logging on to Moodle, clicking on Chemistry class, and clicking on "Webassigns, or you can go to webassign.net. To log in, your username is your ID number, the institution is glenbrooksouth.il, and your password is your ID number.