3.15.11

Announcements: Our test for this new section will either be on Friday the 25th, or Thursday the 24th depending on which day we have a Chem day. Mr. Paek also informed us that we only have 2 more major sections and then we're home free, which is extremely exciting.

In Class: Today in class we did the Heating Curve Lab:

Items Needed: Beaker filled 1/2- 2/3 way with ice, hot plate/burner, thermometer in Celcius.

Procedure: We took a beaker filled with ice cubes and put it on a hot plate/burner. We then every 30 seconds wrote down the temperature of the water at the time. After the ice had melted you were still supposed to write the temperature, up until 3 minutes after the water had started to boil. When you're done with this, you need to make sure that you write down the temperatures and times. Then you needed to answer the usual questions on the sheet and make a graph with the time on the X-Axis and the temperature Y-Axis. (Reminder: Have a title for your graph, and name the x and y axis. Mr. Paek said he'd be grading these for accuracy)

Homework: Finish the graph and answer the questions!

2/7/2011

Going on from stoich we are now on limiting reactants. This concept is pretty basic. You start out with a given amount of grams for two elemnts and you have to figure out how much you can use to make a new one. Basiclly how much of each ingrediant you need to bake a cake. You then find one reactant which is limited. Lets go into a practice problem. Identify the limiting reactant in each of the following cases. 1.0 grams of h2 and 1.0 grams of O2. This is a two step solution.
First start with what you are given 1.0 grams of H2 multiply that by 1 mole over 2 grams of h2.(2 grams comes from finding the mass of H2). Next use the moles from the equation. Which would be 2 Mols of H20 over 2 moles of H2.(You dont get moles of 02 but H20 for both problems0. After doing the math you should get 0.5 mols of H20. Next is doing the second part except backwards. Start with 1.0 grams of 02 this time and to the same math. You would get .0625 mols of H2O. This would mean 02 is the limiting reactant because it is the lowest.
The problems get more complex like instead of moles you have to convert to grams so you just add and extra step add the end. whatever the grams of the elemt you are trying to find over 1 mol. Thats basiclly it. You are given two reactants and you have 2 problems. Just remeber to use the mole of the equation in the problems for the mass produced.

Homework-page 27 #2,page 29 #2 pages 30 and 31
Next scriber-Rachel Mitchel

2/3/11

Announcements- There is a quiz tomorrow (if no snow day) ...but since there is one, the quiz will be probably on Friday.

Today In Class- We went in further in the unit, this time we learned about solving for Density.To figure out how to solve for the Density of X, you need to first figure out the "given" of the object. For example, on page 23,
#1 a) What mass of oxygen is required to produce 65g of CO2?

b) If the density of O2 is 0.00143 g/ml, what volume of oxygen is this?

When figuring out the density of a problem, you DO NOT do anything different all you do is add one more step into the equation and then solve.
another example is on page 24, #3



Homework-Page22., Page 23. #2c, Page 24. 4 &5

Homework: Complete pages 18, 19, and 20 in Chem. Journal. Study Gram to Gram problems.

Announcements: Quiz in class today on simple Stoich problems. Mr. Paek did a class demo to show how oxygen reacts with gas. You should have a good understanding on Gram to Gram problems, if you are struggling go to TLC or talk with Mr. Paek.

Demo: Mr. Paek set up an experiment to show the equation CH4+2O2 --> CO2+2H2O. First he filled an empty paint can completely with gas from the bottom hole. There were two holes, one at lower side, and one at top of lid. Once the can was filled with gas, he lit the top hole and it gave off a flame. While the fire is lit, the amount of CH4 goes down, while the amount of Oxygen goes up. Overtime the flame got smaller and smaller because more oxygen filled the can by entering the lower hole. Once the amount of oxygen is double than the amount of CH4, the can gave off a explosion/sound. The point of this was to show the reaction of the equation above.

Grams to Grams Problems: Before staring the equation, make sure the initial given equation is balanced out correctly or else all your answers will be wrong. "MnO2+4HCl --> MnCl2+Cl2+2H2O" is correctly balanced. To start, when you are given a certain mass, you always put it at the beginning of your equation. Then just like the beginning of the unit, the next step is to change grams to moles by looking at the periodic table. The mass you find will be at the bottom of the line and "1 mole" of the certain atom will be at the top of the line. Next since your equation is at moles because "mole" is at the top of your line, now you can transfer over to another atom. Look at your balanced equation and see how much of a certain atom is equal to the other. Such as "how many pieces of bread do you need in order to make X amount of sandwiches?" If i use "x" and "y" to express the two different atoms, it should look like this. You should have your original grams of "x" times mole"x"/gram"x" times mole"y"/mole"x". Now that you have the mole "y", you want to convert "y" to grams. So you would put 1 mole of "y" under the line, and grams of "y" (found on periodic table) over the line. So now you should have grams"x" times 1 mole"x"/gram"x" times mole"y"/mole"x" times grams "y"/ 1 mole "y".

If this is still confusing visit Mr. Paek or the TLC for help because there will be a quiz soon.

Friday, January 28, 2011

Anouncements : Quiz Monday

Today in class : Today in class we learned stoichiometry. The basic idea is to use a balanced equation to figure out how much of one substance you would need to react with another. The simplest way to explain it is with the sandwich analogie. Lets say the basic recipe for a ham sandwich is 2 pieces of bread (B), 1 piece of cheese (C), and 3 pieces of ham (H). This equation would look like this: 2B+C+3H -> BCH. Using this equation we could find out how many sandwiches we could make with 6 pieces of ham or how many pieces of cheese we need if we have 14 pieces of bread. With the same equation we could also figure out how many pieces of bread we would need for 3 sandwiches. With smaller and more basic numbers like these we can solve the equation in our heads without much effort; however, when we have larger amounts like 33 pieces of ham these equations become more difficult. If we were trying to find out how many pieces of bread we need with those 33 pieces of ham we would have to multiply it by the ration of bread to ham given to us in the original equation. In this case it is 2 pieces of bread over 3 pieces of ham. In order to solve this we need to take the starting information of 33 pieces of ham and multiply it by the ratio 2 pieces of bread over 3 pieces of ham. It is important to remember that when you set up the problem that the same units always cancel out. That is why the 3 pieces of ham must be on the bottom in order to cancel out the 33 pieces of ham given to us in the starting piece of information. Now in chemistry, instead of sandwich ingredient we use molecules and elements. The ideas however are exactly the same. Take a balanced equation and use the information given to find the amount needed to cause a chemical reaction. We also learned how to find the exact mass of elements that we would need in order to cause a reaction. Back to the sandwich analogise, if a piece of bread weighs 2 grams, a piece of cheese weighs 1 gram, and a piece of ham also weighs 1 gram then we can find out the weight of a sandwich ingredient needed to make the sandwich. If we had 2 grams of cheese, in order to find the amount of ham needed we would multiply the starting amount by the amount of cheese needed to make 1 sandwich which is 1. So 2 grams of cheese equals 2 pieces of cheese. To convert that to ham we would multiply that by the ratio of ham to cheese 3pieces of ham over 1 piece of cheese. this gives us 6pieces of ham because the cheese cancels out. Finally to find the amount of ham in grams we simply multiply the 4 pieces of ham by the 1 gram each piece of ham weighs. When you put all this together you it ends up meaning that for 2 grams of cheese you need 6 grams of ham to make the sandwiches. Again, in chemistry we use the same concept but instead of grams of ham we use the molar masses to find the amount of a substance needed to cause a chemical reaction.

Homework : Pages 15 and 17

Announcements : No Announcements Today.

Homework: None. You should have pages 1-8 already completed.

Today In Class : We did not do much in class. To start of class we grabbed pages 9-35 and taped them in our journals. The pages went about two pages per paper. Before taking the first quiz out of 7, we reviewed a little bit. we talked about how to convert grams molecules atoms and moles. We then took the quiz.

There is a total of 7 quizzes. each worth 7 points. 49 points possible. if you get 7 perfect scores you will receive extra credit. also if you receive 5 perfect you will get extra credit but a little less. same goes for 6 perfect scores. You will need to get at least one perfect score to take the end test.

To end class we had a power point on stoich. for the power point we worked on page 10.

Wednesday, January 26, 2011

Announcements : -If you have any questions about moles find Mr. Paek ( he is free 5th and 6th period.) This is a really important unit and if you want to do good on the test you have to do good on the quizzes.

-Make sure to show all work and units in homework and quizzes, because it will get very confusing later on if you don't get in the habit of doing it right now.

- Buy a notebook if you haven't already.

- First quiz tomorrow/ 7 quizzes total this unit.

Homework: -pages 7-8.

Body: Today in class we went over some problems from pages 1-6.(Again: make sure that you go get help from the TLC or Mr. Paek if you don't get something.) Then we did a lab called: Moles Stations Lab. The lab had 9 stations, and in each one of them we calculated either the mass number, mole, or the number of atoms.

Set1: had to count the number of pairs of shoes in the room.

Set2:find the mass of Aluminum foil and find its mass number and how many moles it had.

Set3:find the mass of a carbon rod find mass number of it and how moles, then how many atoms.

Set 4:we had to find how many moles of Krypton in a graduated cylinder, and the mass of it.

Set 5:we had to find the mass of H2O, and the number of grams in one mole of H2O.

Set 6:find one mole of HCl, the number of moles in it, and the number of molecules.

Set 7:found the volume of an aluminum bar its density and the number of moles and atoms.

Set 8:find the mass if neon, and the number of atoms in it.

Set 9:find the mass of a balloon and the balloon's mole.

***examples from some problems in the lab:***

set 2: 1)The mass of Aluminum foil=3.74g

2) The mass from the periodic table = 27 g/mole

3)Number of moles Aluminum foil has=3.74 g Al foil*1mole/27g of Al foil=0.14 moles of Al.

set3: 1) Mass of carbon rod= 4.35 g

2)Mass from periodic table= 12 g/mole

3)Number of mole in this carbon rod= 4.35g carbon rod* 1mole/12 g carbon rod=.36moles

4)Number of atoms in rod=.36mol*6.02E23atoms of carbon/1mole=2.16E24 atoms of carbon