GRADES HAVE BEEN UPDATED!!!

I have just updated grades. Some individuals are missing minor assignments (like the signed Lab Safety Contract and Class Policies and Procedures), but because there are very few grades to buffer a bad grade, those individuals have very poor (I'm talkin' "F"!!) grades. Please look at your grade and get the required material to me. The Lab Safety Contracts and Class Policies and Procedures can be found on my teacher pages. I think that activities start taking grade reports this Wednesday for eligibility, so the sooner the better for rectifying the situation.

Density of Pennies Lab and a Movie

Remember, the write-up for the Density of Pennies lab is due at the beginning of class on Monday, 8/30/2010. It must be either written out neatly or typed (just a hint, typing pleases me and I may be kinder when grading). Please follow the seven step format of the Formal Lab Report sheet that you were given last Thursday. Please look over the pointers that I have bulleted below:

• We have covered the Purpose and Theory statements in class, so I am not going to address those points again.
• Be short and to the point on your procedure. The following is a good example of the amount of detail that you should include for a particular step. "Found the mass of pennies and weighing dish to the 1/1000 of a gram. Repeated this step for both categories of pennies."
• The Data Table should easy to follow and include all units of measurement. Do not perform calculations (other than a final measurement being subtracted from an initial measurement) in the data table.
• Sources of Experimental Error (SEE's) should address matters of procedure or technique that may cause measured values to be slightly inaccurate. These need to well developed ideas, so a paragraph may be needed to completely explain an event that would cause error to be introduced into measurements taken during the lab. You could have multiple SEE's associated with a lab.
• Your Conclusion MUST address if the Theory used was able to achieve the Purpose. An example could be: "The densities for both penny categories only differed by one tenth of a gram per milliliter. Do to uncertainty of measurement, I do not feel that it is proper to declare that there is a definite difference in how the pennies were manufactured (minted) prior to 1982 and after 1982." Also remember, you must always include a statement on how you would improve the lab if given the chance to do it again.

Please click on the link Density Lab. I have made a Vodcast (not Podcast) of a fictitious scenario that will hopefully illustrate to you an emphasis that I made to you about having as large sample as possible. The Vodcast also addresses points to the write-up. It is hosted on a website called "TeacherTube". You may have to sign up for "TeacherTube" prior to watching the video. Please be prepared to answer questions (maybe in the form of a quiz) that relate to the lab on Monday. Have a good weekend.

Lab Tomorrow and Extra Credit Opportunity

Tomorrow you will be performing your first "official" laboratory experience for a grade. Your only expectation for preparing for the lab is to write a Purpose statement for the lab and to also write a Theory statement. Remember, you are going to try and confirm if the minting (manufacturing) process for pennies changed in 1982. You are going to use the physical property of density to distinguish the different categories of pennies. Since you will be measuring in this lab, you MUST incorporate precision and accuracy of measurement and proper use of precision and significant figures in calculations. The validity of your results depends upon it.

**Extra Credit Opportunity** If you bring in a 4-pack of AAA batteries, you will receive 10 points extra credit towards your homework portion of your grade. The purpose of me (Mr. Brueckner) stockpiling batteries is two fold. First, it supplies the calculators that I allow students to use in class with batteries. Second, it provides a stockpile of batteries for any and all students enrolled in any of my classes to have a source of batteries if the batteries run out in a student's personal calculator. Remember, I do not offer extra credit on an individual basis, so take advantage of any and all extra credit opportunities when offered. You can bring batteries in through September 3rd. Have a good night.

Liar, liar, pants on fire!!

People probably left class today feeling very much confused as to why I called everyone a liar in class when the results of the area of the science department were displayed. Now, don't feel offended if I called you a liar, I do not think ill of you. I do take issue with almost everyone's reported area value. Below I will explain why.

First it has been established that every measurement has uncertainty built into it due to the estimation of the last digit of any measurement. Also, the nature of the procedure introduces error. Since the measuring stick (a.k.a "The Brueckner") had to be slid along the floor end to end over 25 times, it is inevitable that the length measurement will be off by not starting at the precise location that the last measurement ended. This and many other errors could be found in your technique. This is why we never say the "E" word when discussing measurement.

You used two length measurements (which both contained uncertainty and probably error) and multiplied them together. Not only did you multiply the magnitude of each measurement, you also muliplied the error of each measurement by over 25 times. Therefore, any group that reported an area meausurement with more decimal places than what was originally present in the measurement cannot guarantee that calculated value.

These are example from 7th hour:

27.6 B x 32.7 B = 902.52 B^2 --> This should have been reported as 903 B^2
29.63 B x 25.90 B = 767.417 B^2 --> This should have been reported as 767.4 B^2
30.025 B x 26.087 B = 783.262175 B^2 --> This should have been reported as 783.26 B^2

All measurements from the above examples are correct. All groups used the correct amount of precision in the length and width measurements. I will discuss the rule that needs to be followed in class tomorrow, but can you deduce the rule from the values that I indicated to be the correct values to report?

Significant Figures vs Place-holder Zeroes

Today we went into a number of different scenarios on when numbers are significant (the certain digits and one uncertain digit of a measurement) and when zeroes are not significant (only placeholders). If you understand the intent of the author of the measured value, you can determine what is significant to the measurement and what is needed only for the magnitude of the number. There are a bunch of rules in Chapter 2 of the book on how to determine significant figures and you are free to use them for significant figure determination, but in my opinion, if you understand the intent on how a measured value was written, you will have an eaier time of significant figure dtermination. Significant figure determination is extremely important once we start using measured values in calculations. This will be covered tomorrow (Tuesday, 8/24) and Wednesday, 8/25.

You should finish through significant figure determination, #15 for tonight. We will go over the solutions first thing tomorrow. Please see me if you have any questions on the material.

Measurement Readings (Cont.) and Error (Systematic vs. Random)

We started the day by reporting the mass values measured the day before on the 4-beam balance. Part of the discussion dealt with systematic error (when an error occurs over and over consistently) and random error (an infrequent, singular event). Example, the fact that the 4-beam balance does not zero is a systematic error. It is consistent as long as you use the same scale, that is why I insisted that you go back to the same lab area that you used the day before so you used the same scale. You kept the systematic error the same because of it. Your data MAY be slightly inaccurate, but you are consistent. If you had changed scales, you would be introducing random error. You values would vary due to different reasons (in this case a different scale). Therefore, there would be no consistency in error and you could not factor out the error because it would be constantly changing, thus a different fix would be needed each time.

Please finish the graduated cylinder (volume) readings and thermometer readings (temperature) on the packet for tomorrow.

Measurement_Precision_And Why We Will Never Say The "E" Word

Today we covered quantitative (measured) data collection. This type of data would include mass, length, volume, time, etc. We discussed precision and the limitations of measurement. We discussed the uncertainty associated with all measurements because of the estimation of the last digit of all measurements. For this reason, it is not proper to say the word "exact" when discussing a measurement. Exact implies that you can guarantee the measurement without any question. The problem with making that type of guarantee would be if another individual made the same measurement with a more precise instrument and found a value different than what you reported, you would be liable for guaranteeing the value. This is an extreme example, but you should use a term like precise. That gives you some wiggle room.

When can you say "exact"? Believe it or not, you can. When counting, you can say exact because there is no question that you have ten toes or 96 french fries (as long as you are careful counting).

Please finish the first page of the measurement worksheet tonight for homework. The page covers how to read 3 and 4 beam scales (balances). We will go over it first thing tomorrow. Please bring with you the piece of paper that has the mass of the card found in class today.

Chapter 2 Overview

Your only assignment for tonight is to go over chapter 2 in the book and do a self assessment of material in each section of the chapter. On a piece of paper, write the section number (example-2.2) and just answer if you are familiar with the material or not. Examples: Yes, I know this. No, I have seen this but I do not remember it. No, I have never seen this material before. I just want an idea of what individuals are comfortable with.

First Day of Class

Welcome to Mr. Brueckner's chemistry class. I hope that we have a really good year together. You need to complete the following by Friday, August 20th, 2010.

1. Print a copy of the Classroom Policies and Procedures found on Mr. Brueckner's Chemistry page. The copy needs to be signed acknowledging that you and your parent(s) / guardian(s) are aware of class expectations and grading policies.
2. Print a copy of the Lab Safety Agreement, which can be found on Mr. Brueckner's homepage. The agreement must signed by you and your parents. Read over the safety contract and be prepared for a 20 question lab safety quiz on Friday, August 20th, 2010.