Wednesday, December 15, 2010

Today Mr. Henderson started off class with some announcements. First of all, Friday is the test, and he is going to be collecting lab notebooks. Second of all we only have to do 2 out of the three webassigns due Friday. Another reminder, delicious assignment is due tomorrow.

Next Mr. Henderson passed out the lab grading sheet and explained a little about how the lab is going to be graded. Mostly just reviewing whats on the sheet. Later on i will explain more on how to help you finish the lab. After that we went on page 30 and Mr. Henderson gave us the answers to the reading sheet along with some notes: pressure has a direct relationship with the amount of moles of a gas, therefore pressure1/pressure2=moles1/moles2.

The answers to the reading sheet are:

1) A, C

2)A

3)A

4)287

5)570

6)c

7)A).25 B).25 C).50

The next thing we did was page 19. (I will include a picture at the end of this blog and go over number one) first of all we needed to find the vapor pressure from a chart in our book on appendix 1. For this problem since the temperature was 30 C when you look on the chart the v.p. is 31.8 mmHg. Then we need to convert the kPa to mmHg since the other pressure is in mmHg. After that we can conclude that PH2O is 31.8 mmHg since that stands for the water(vapor) pressure. The O2 pressure would be the over all pressure, which we found by converting 120 kPa to 900.1 mmHg, is the total pressure minus the vapor pressure, which is 900.1-31.8=868.3mmHg. Then the next two questions ask for the fraction pressure of H2O which we find by putting H2O's partial pressure untop of the overall pressure, 31.8/900.1 which equals .0353. Next we find the fraction pressure of O2.Which we find the same way as the fraction pressure of H2O except different numbers, so its 868.3/900.1=.9646. The rest of the answers you can see on the picture.

After that Mr. Henderson helped us do most of our lab which the rest were finishing tomorrow. I will show you my data, which you can plug your own numbers in if need be. My data is : .03582g Mg, temperature is 20.5, volume of H2 is 38.2, and by using appendix 1 v.p. is 17.54. So using my grams of Mg i convert, using stoichiometry, to moles of H2. Which i get .00147407 m H2. We are trying to find the volume of H2 at STP. Now using the pressure of the room, which Mr. Henderson gave us, and the pressure of the H2O we can find the pressure of H2 which we need to find the Volume of H2. You subtract H2O pressure from room pressure, 763.52-17.54=745.98mmHg, which is the pressure of H2. Now we use the equations P1V1/T1= P2V2/T2 to find the V2. When plugging in numbers make sure to convert Celsius to Kelvin. (745.98)(38.2)/293.5=(760)V2/273. V2 is 34.87 L. That is all we managed to do in the shortened class periods. As I said we will finish the lab tomorrow.