Tuesday, January 25, 2011

This morning, we walked into class and Mr. Henderson passed out our semester grade reports. Once he was sure that everyone had received their grades, he asked us to turn to page 31 in our Thermochemistry unit packets. He gave us the answers for last night's WebAssign:
1. False
2. B
3 D
4. C
5. B
6. D
7. A
8. B
9. D
10. True
11. A, B, C
12. D, A, C, B
13. A
14. A

Subsequently, Mr. H told us to get out our lab notebooks while we looked at Daria's blog. As he read through it, he explained to us what was happening at the molecular level during state changes of water. First, the particles in the solid crystal lattice begin to vibrate when thermal energy (heat) is added (temperature increase). They wiggle more and more violently until they turn into a puddle (liquid). The fluid particles have small intermolecular forces and are relatively close together. When heat is added, they begin to vibrate and move about the puddle until so much kinetic energy is gained that the molecules "pop" out of the puddle and "fly" (as Matt said) because they are now a gas. Particles in a gas are far apart and if one were to walk through gas, there would be no resistance. Particles in a liquid are semi-close to each other and if one were to walk through liquid, there would be slight resistance. However, particles in a solid are very close together and if one were to walk through a solid...they wouldn't! Mr. H reminded us: "You can never walk through a solid."

We then turned to our TC9 lab in our notebooks. Mr. Henderson told us that we must tape our data table and graphs into the lab. We also must write a conclusion/discussion, answering all 4 questions required in a fluid manner

1. Observe the plateaus on the two graphs. What could be happening during these plateaus?

2. Determine the melting point and freezing point of lauric acid. How do they compare?

3. Describe what happens at the particle level as heat is added to the substance and its temperature increases.

4. Describe what happens at the particle level as heat is added to a substance and its phase changes.

Henderson instructed us to take some notes:

• A plateau does not equal [Delta] T
• Melting point and freezing point are the same temperature! For lauric acid, it's 44 degrees Celsius
• Plateau = mix of solid/liquid or liquid/gas

After discussing this, Mr. H gave us 5 minutes to work on the conclusion. Then, he said that there would be a demo in the back of the class later on involving boiling water and capturing the emitted gas.

Even more after, we turned to page 13 in our Thermochemistry packets. First, we did numbers 1-13:

1. D E F

2. A

3. F

4. NONE

5. A

6. D

7. D E F

8. E

[oops, where's the 9?]

10. B

11. E

12. C

13. D

The bottom of page 13 is as Mr. Henderson said "basically lab TC9" except with water. The labels for the diagram are: 1 - solid, 2 - solid/liquid (0 degrees), 3 - liquid, 4 - liquid/gas (100 degrees), 5- gas. Then, we turned to the next page (14) where we completed questions 15-28:

15. 2, 4

16. 4

17. 1

18. 2

19. 2

20. 2

21. 4

22. 5

23. 2

24. 3

25. 4

26. 1, 3, 5

27. 2

28. 4

We migrated to the back of the room to finish the demo. Mr. H connected a thin copper pipe to the flask with the boiling water. We observed as steam spewed from the end. We thought this was gas. NO! It was water!!!!!!! As the gas traveled through the pipe, it cooled back to liquid state. Mr. H then put the burner under the pipe. He showed us that this was real gas. It was SO hot that he could light a match! Then he placed a paper at the end, which he burned "I'M HOT" into. Then the bell rang.

Homework: WebAssign Due Thursday the 27th, page 15 in packet

Thursday, November 18

This morning, we walked into class and were notified that there was a lab today. The lab is called ST1 Copper and Silver Nitrate Lab. The purpose is to use careful measurements to determine the mole ratio of copper(II) and silver in the single replacement reaction of silver nitrate with copper. We were instructed to take out our lab notebooks and copy down this purpose onto a clean right-side page. On the left side, Mr. H told us to write the chemical equation for the reaction, for it would be helpful later. It is:

Cu (s) + 2AgNO3 (aq) --> 2 Ag (s) + Cu(NO3)2 (aq)

We all then received a piece of paper describing the lab's procedure. 2 people from the lab group were to carry out the first procedure while the remaining 2 were to carry out the second procedure. The procedures are as followed:

1) Prepare the Silver Nitrate for Reaction:

• Mass an empty 50 mL beaker. Record.
• Add ~1.4-1.6 g of AgNO3.
• Mass beaker plus AgNO3. Record.
• Add 30 mL of water.
• Stir to dissolve solid; rinse stirring rod so as to avoid loss of the AgNO3.

2) Prepare Copper for Reaction and React:

• Obtain ~25 cm of copper wire.
  
• Mass wire. Record.
  
• Loosely coil the wire so as to rest of a wood splint as shown. It should be long enough to hang on the wood splint and dangle in the solution. Yet it should not touch the bottom of the beaker.
  
• Add 3 drops of nitric acid to the solution; avoid contacting the copper wire with the HNO3. Do not stir.

After we did what was required, we were instructed to leave our notebooks at our lab benches and come back to our seats. This time was set aside for the reaction to occur. When we were back at our desks, Mr. H told us to take out our packets and turn to page 6 for

E V E N M O R E S t o i C H E o M I S T R Y!!!!

Mr. H told us to do number 7; write the balanced equation for the synthesis of magnesium oxide from its two elements - magnesium and oxygen. The answer is as follows:

2Mg (s) + O2 (g) = 2 MgO (s)

Then we were told to do number 8; calculate the molar mass of each of the three reactants and products. The answer is as follows:

Mg: 24.305 g/mol O2: 32.0 g/mol MgO: 40.3 g/mol

After, as a class, we went through the next three problems and identified how many steps would be needed (using the Mole Island method, of course). Number 9 was a one step equation. Number 10 was a two step equation. And number 11 was a three step equation.

The answer to number 9 (Determine the number of moles of magnesium oxide produced by the reaction of 3.25 moles of magnesium.) is 3.25 molecules of MgO, simply found by using Mole Island to convert from moles of magnesium to moles of magnesium oxide.

The answer to number 10 (Determine the mass of magnesium oxide produced by the reaction of 5.22 moles of magnesium.) is 210.39 g MgO, again, simply found by using Mole Island to convert from moles of magnesium to moles of magnesium oxide to grams of magnesium oxide.

The answer to number 11 (Determine the mass of oxygen gas which will react with 65.2 grams of magnesium.) is 42. 92 g O2, aaaaaaand again, simply found by using Mole Island to convert from grams of magnesium to moles of magnesium to moles of oxygen to grams of oxygen.

Before we knew it, it was time to check back at our lab. Our whole lab group was to do the third and fourth procedures listed on the sheet of paper:

3) Retrieve Silver Product from Copper Wire:

• Obtain a clean, dry 100 mL beaker. Using a permanent marker, label it with your period and your names.
• Mass the empty beaker. Record.
• Carefully lift the copper wire (with silver attached) from the beaker.
• Hold wire over and into 100 mL beaker and rinse with a forceful stream of DI water. The goal is to knock the silver off the copper and into the beaker.
• Continue rinsing until all the silver crystals are removed.
• Set labeled beaker aside to dry. Once dry (the next class period), mass the beaker with the silver. Record.

4) Rinse and Mass Unreacted Copper:

• Rinse the remains of the copper wire in an acetone bath.
• Being careful not to break or crumble the copper, thoroughly dry it by dabbing it with a paper towel.
• Mass the remaining copper wire. Record.

We did just that. The untouched product (silver still connected in the original beaker) should look like this:The removal of the silver should look like this:

Mr. H then told us to clean up and reminded us that we would be finishing the lab tomorrow.

The homework is the Stoich WebAssign 2.

Wednesday, September 15

We began today's class by briefly looking at the blog. First, we looked at Konstantine's delayed blog from last Friday (due to technical difficulties, of course) and Katie's blog from last night. Mr. Henderson then proceeded to give us a brief lesson on how to use DropShots with the blog. This link provides the portal to the "Chemistry Classroom" account with the access password being "gbs":
http://www.dropshots.com/chemistryclassroom

While showing the class Katie's blog, Mr. M noticed that Katie had embedded an link with excellent practice into her blog. This reminded him of telling us about the Delicious assignment that we have due on Friday, September 17. He said that Katie's link was a perfect example of what we could use for our assignment. He showed us how to log into the database and how to tag and fill out the form for our links. In order to log into this website, we need a Yahoo account. Mr. H told us that it would be useful to have a Yahoo, Google, or Facebook account because those major corporations would end up taking over many of the smaller companies. Thank you for those wonderful words of wisdom, Mr. H! More thorough directions for Delicious can be found on the hand out we received in class on Monday or on the GBS Chem-Phys website:
http://gbschemphys.com/honchem/index.html

After our tech tutorial, Mr. Henderson asked us to take out our unit packets and turn to page 9. Before beginning the worksheet, he quickly reminded us of the differences between a physical (describing the substance without describing its interaction with other substances) and chemical (describing the substance by how it interacts with other substances) properties. To give us a better idea, he told us he would show us an example of a chemical property of magnesium. He showed us the sample of magnesium - a shiny metal - and turned on the methane flow. He lit the burner (from the bottom up, of course) and began to burn the magnesium. Mr. H told us that magnesium reacted very strongly with oxygen to make magnesium oxide and that we should be prepared to see a very bright light, indicating the reaction. Sure enough, when the magnesium heated up enough, we saw a very bright light. Our experience was similar to this video from Youtube:
http://www.youtube.com/watch?v=Q_LU1EASadU

Mr. H then pulled up an overhead of 4 out of the 5 pieces of evidence of a chemical change. They are: bubbling & production of gas, formation of a solid, heat or light, color changes, or temperature changes. The difference between a heat/light change and a temperature change is that the temperature change is more drastic and long term.

As soon as all the explanation was finished, we began page 9 and the "Verbal Description of Change" section. We attempted to do the section individually and went over the activity together and the answers are as followed: C, P, C, C, C, P, P, C. We had to be on the lookout for the chemical changes we learned about in each of the scenarios order to determine the type of change.

Next, we determined the "Symbolic Description of Change" as a class. If the element remained the same, it was a physical change. If the before and after differed from each other, it was a chemical change. The answers are as followed: P, C, C, P.

To finish the page, we flipped it over and determined the "Visual Depiction of Change at Microscopic Level". We had to be on the lookout for changes in the shape and arrangement of the atoms and molecules. The answers are as followed: C, P, C, P.

Abruptly, Mr. H got up and directed us to the back of the room and under the fume hood. He asked us for two pennies. He took our a large bottle of nitric acid and explained to us what a hazardous chemical it was and how we had to be careful when handling it. Mr. H was going to demo the reaction between copper and this nitric acid. He poured the acid into a flask and diluted it with some water. He dropped one of the pennies in and told us to observe. Meanwhile, he took another flask and filled it with pure nitric acid. He dropped the copper penny into the substance and told us to observe and compare it to the other flask. Immediately, we saw a change of color. The acid went from clear to a gradient green-red. Bright orange gas began spewing out of the top of the beaker. It bubbled and displayed a clear chemical change. The diluted beaker was showing the same changes (minus the color change and significantly less bubbling and gas) at a much slower rate. Mr. H ask Katie to touch the beakers carefully. She told the class they were both very warm, indicating a temperature change. It was very interesting to see the copper penny dissolving and reacting with the acid. The flask with the pure nitric acid and penny looked similar to this photo:

We concluded the class by returning to our seats. Mr. Henderson quickly read us a story about a man whose experience with nitric acid inspired him to keep experimenting with it. With little time left, we were instructed to turn to page 11 and complete the "Verbal Description of Change" and determine the Physical and Chemical properties. The answers are as followed: P, C, C, P, C, P, C, C, P.

Just as the bell was about to ring, Mr. H handed out the quizzes from last week and told us to check our answers and use it as a guide. He told us that tomorrow we could expect a lab about density and that our homework was finishing the 1.2 Webassign and our Delicious assignment.