12/13/10

Announcements: Study for test on Thursday.

Homework: chem packet (due Wednesday) , and finish double replacement lab

Today in class we worked on the Double Replacement Lab in class. Mr. Paek explained how to mix the elements to see if there would be no reaction or a reaction. To do the lab you need to set up a data table that shows all the chemicals. Like this.

Then you mix each chemical once with the ones on the the grid and mark an which ones have a reaction, if there is no reaction write NR.

Next scriber: Mike A.

12/8/10

Announcements: do your homework and study! Quiz tomorrow!

Homework: Complete chemthink tutorial and quesitons (chemical reactions)!

On this day (late arrival) we learned about different reaction types:

1) Single Replacement

2) Double Replacement

3) Synthesis

4) Combustion

5) Decomposition

During single replacement, one element replaces another element in a compound. This kind of reaction consists of three elements: AX+Y. In this case A and X attract because they have the opposite charges (+ and -) while Y has a possitive charge. During single replacement, the product will end up being AY+X because now element Y has replaced element X. Example:

Since both copper and iron have a positive charge, they switch.

During double replacement, the positive charged elements and the negative charged elements switch places. This kind of reaction contains 4 elements: AB+XY. In this case A and X have positive charges and B and Y have negative charges. During the reaction, these elements switch pairs: AY+XB. To make it simpler, here is another example. There are two couples: AB and XY. A(boy) decides he doesn't like B(girl) and starts dating Y, and vice versa. Another example:

During synthesis, a 2 elements join together to form a complex compound. This reaction type is much easier to learn. An example: A+B=AB.

During decomposition, a complex compound seperates into two elements. Its the exact opposite of synthesis. An example: AB=A+B

Combustion is the reaciton of oxygen gas with anything. Combustion always and only contains oxygen carbon and hydrogen. It is the easiest reaction to learn because the answer is always CO2 + H2O. After this, all you have to do is balance the equation. Example:

Next scriber... IS PEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEETER I.

12/06/2010

Announcements: We will have two quizzes, none will be dropped. Homework will be assigned.

Homework: None


In class we learned about chemical reactions, and how to solve them. We started the day with atom counting. In atom counting, you have a formula and you count how many of each element there are. Ex. (2C+2O) There are 2 carbons and 2 oxygens in this formula.


Also we studied reactions and how they look. Ex. (N2+O2) the diagram would have both nitrogens attached to each other while the two oxygens will be attched to each other. The reaction is that both nitrogen and oxygen split and go to the opposite. the final balanced formula would be 2NO.
















Finally we went over balncing equations. He told us that the whole point is to make both sides equal for it to be balcnced. Also another thing was that the reaction is the product. Ex. 2Al+3Pb(NO3)2 -------> 2Al(NO3)3+3Pb. The numbers in red are what make it even.
Next Scriber: Ross

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.

Today in class Mr. Paek went over any questions we had about the Lewis structure.

The Lewis structure is the drawing we draw with the dots. Today we got new worksheets; we got pages 16-20 and, learned something new. We learned about molecularshapes, and how to draw the shape.

There are different names for these shapes: linear, trigonal planar, trigonal pyramid, bent, and tetrahedral.

The name of the shape is linear id its 180 degreesand is on one flat plane. The shape of a linear would look like this:

The name of the shape is trigonal planar is there are three bonds, no lone pairs, and are on one plane. The shape of a trigonal planar is:

The name of the shape is trigonal pyramid is there are lone pairs of electrons, and if it is three dimensional. It would be three dimensional because, the lone pairs would go on top and push the three other bonds downward, making the shape look like this:

The name of the shape is bent if there are two bonds and the lone pairs push the two bonds downward. A bent shape would look like this:

The last name we learned is tetrahedral. Tetrahedral is just like trigonal pyramid, but rather than the lone pair it has an extra bond. The extra bond will push the other three bonds downward. A tetrahedral shape would look like this:

When drawing any shape, first look at the Lewis structure of the element, and only draw in the dots for the center element, but draw in the correct amount of bonds. When drawing a trigonal pyramid the three bonds should be facing down because of the lone pairs of electrons forcing it to go downward. Also, the two pairs of bonds for the bent shape is also facing downward because of the lone pairs of electrons. Same with the tetrahedral, because of the extra bond it forces the 3 other bonds to go downward. (the pictures are shown above).

Homework:- finish pages 16-19 (new work sheets we got today) and the two worksheets given on Friday are due tomorrow for credit.

Upcoming quizzes or tests:- there is a quiz tomorrow. The test is after Thanksgiving break.

Next Scriber:- Tima Tito

11.18.10

Announcements:

1. Tomorrow is Chem-day in the Lyceum.

2. On Tuesday, the day before break, we will have our lab test for this unit.

AFTER BREAK

3. On Monday 11/29/10, we will have a quiz.

4. On Tuesday we will have another quiz.

5. On Wednesday, December 1, we will have our unit test.

Homework: none.

Today in class we first got pages 25 through 30. Then we officially begin the class by going over the worksheet that we worked on Wednesday with the substitute. There were two major problems that we worked on which were C2H2 and C2H6O. For C2H2, the correct Lewis structure was: H-C=-H. (The double bond is suppose to have another line on top, so after the C is three lines.) The second problem that students were confused about was C2H60. The Lewis Structure for this molecule is a bit too complicated, but it not something you should worry about so much.

Next we went over polar and non polar. As a reminder, polar means unequal or different, and non polar means equal or same. Make sure that you understand those two terms completely so that the future will be easy for you. After we reviewed a little bit about non polar and polar, we did page 25. Then we started a lab.

This lab starts on page 27 and is called "Polarity Olympics: The Trials". First on the page, we decided what the charge of each molecule was in H2O. The two Hs' have an electronegativity charge of 2.1 The oxygen molecule has a charge of 3.5 and because it has a higher electronegativity, it has a negative charge. The two hydrogen atoms have a positive charge. After doing the first page together as a class, we then finally began our lab.

(Page 27)

In the lab, we used a penny, water, hexane,watch glasses, capillary tubes, markers, and two cotton swabs. For the first part of the lab, we put many drops of water onto a penny until it overflowed. We recorded the number of drops and then drew a side view of the penny. We did the same procedure twice a second time, but instead of water we used a liquid called hexane. From our results, water had the most drops than hexane. We observed that hexane evaporated a lot faster than water did when it touched the table.

For the second part of the lab, we used capillary tubes and watch glasses. We put 10 drops of water onto one watch glass and hexane onto another. The we took the capillary tubes and touched them with each liquid separately. The capillary tube that held the most liquid was hexane.

The third part was easy just like the previous two parts. The point of this trial was to clean two types of marker from the glass. On one watch glass we drew a line with permanent marker and on the other, we drew on it with a transparency marker. Then we put water on a cotton swab and wiped the transparency marker. The transparency mark went away and the cotton swab turned green. With the same swab, we wiped the permanent marker, but it didn't go away. Next we put five drops of hexane onto a new cotton swab and wiped the transparency mark, but it didn't erase. When we wiped the permanent mark with the hexane filled swab, the mark went away. From our data, we concluded that water erased the transparency mark, but not the permanent mark and hexane erased the permanent mark , but not the transparency mark. The water and hexane were opposites.

This was the lab we did today and it was pretty easy. We ended the class by cleaning up our mess. Also our lab test is most likely going to be somewhat similar to this one! If you have any questions about anything, be sure to ask Mr. Paek for help!

Next Scriber: Petrina Z.

11.09.2010

ANNOUNCEMENTS: 1. There will be a total of 6 quizzes, one everyday 2. If you're absent before a quiz, that quiz will be the one that's dropped 3.You can drop one quiz and retake one quiz 4. We taped in pages 9 to 15

HOMEWORK: Finish pages 11 to 13

Today in class we learned how to make Lewis dot structures for formulas like CH4 or F2 and others like the examples below:

Before drawing the actual structure, Mr. Paek suggests doing N, H, S and B every time because it makes it a lot easier. These letters stand for Need, Have, Share and Bonds. 

• NEED: you put the number of electrons needed to be stable, for most elements it's 8, but for Hydrogen it's 2. Then add all of it together.
• HAVE: the number of valence electrons then add it all up. 
• SHARE: subtract the number of valence electrons from the sum of the electrons needed. 
• BONDS: you divide the number shared by 2.

For example: The formula SeF2

• N= 24 (Se needs 8 electrons and F2 needs 2 sets of 8 because of the subscript "2", so you do 8+8+8=24)
• H= 20 (Se has 6 valence electrons and F2 has 7 and 7 because of the subscript "2", then you do 6+7+7=20)
• S= 4 (N-H or 24-20=4)
• B= 2 (4 divided by 2)

Once you're done with all that, you have to draw the structure.Using the same formula SeF2, Se would be in the center with two F's on either side, it doesn't really matter what side it's on as long as there are two F's. The bonds represent the lines from Se to the F's. Each line representing the number of electrons shared, which in this case is four, so two lines represent four electrons shared. The picture also has to have 20 total electrons in it because of the have. Since the lines already represent 4 electrons, you need 16 more, so you draw dots around the Se and the F's. I know this may sound confusing, but the picture below should make it easier to understand. The formula I used for this example is the first one below:

NEXT SCRIBER: Seena K.