Friday, September 17

On Friday the first thing that Mr. Henderson asked the class to do was pull out their Unit 1 Packets and a calculator. He then told the class that we would not be staying here long, we would be going to the computer lab to do some graphing and plotting on a program called Graphical Analysis. Mr. Henderson then took attendance and we started to admire Lindsays very well set up blog post of the day before. Mr. Henderson notices that there is a link to a page with some practice for significant digits. He tells the class that for later blogs if we decided to add a link to our blog we could use that same link for our Delicious assignments.

After we had finished admiring Lindsays

blog it was time to get down to business and take a look at page 13 in our unit packets which had some density practice for us. On the page we

needed to know the formula for density which is, Density = Mass/Volume. It also talks about how the units of density are usually expressed in grams/ml or grams/ cubed centimeters. We then do problems 4 and 5. In problem 4 the density is given as 8.933 g/ cubed cm and the mass is 2.62 g. we have to find the volume of the substance so we use the equation for density and plug in the numbers we know, 8.933 = 2.62/x, in order to solve this problem we will have to use algebra. Start be multiplying both sides by 1/2.62 then we get the answer .293295, this is not the answer because we have not put significant digits into consideration yet. since we

divided we use the same amount of digits of the number with the smallest amount of significant digits which would be 2.62 which has 3. So our final answer for this problem would be .293 cubed cm.

We then go to page 14 of our packets and it is similar to what we do in the computer lab. In the computer lab we plot the volume and mass that is given on page 15 and a graph is made. Then because we have to plot our data from the Dense Cents lab, we plot our information from the Pre 82 and 82 coins and the Post 82 coins.

For homework we had to do 2 webassign assignments, finish labs 5, 6,and 7, because we would be getting them checked on tuesday, and finally we have a unit 1 test on thursday.

Friday September 10, 2010

Today's class started off by getting our lab notebooks back. Mr. H graded Labs 1-4, but didn't tell us our grades in our lab notebooks. He told us that he wrote comments and suggestions in most lab books.

Mr. H then had everyone take out their chemistry packets and he went over the question on the bottom of page 6, which was about listing significant numbers when adding, subracting, multiplying, and dividing. He went over significant numbers again and how many to include when adding, subtracting, multiplying, and dividing. The rules are as followed when adding/subrtracting or multiplying/dividing:

Addition/Subraction: The number of decimal places in the result is equal to the number of decimal places in the quantity with the least certainty (i.e., least number of decimal places).

Multiplication/Division: The number of significant figures in the result is the same as that of the quantity with the least number of significant figures.

Mr. H then worked with the class on the first two practice problems to clarify what the rules were saying. He then had us work on the rest of the practice problems by ourselves. After a few minutes of working Mr. H revealed the answers to the class, so everyone was able to check their answers. He answered a few questions from students and then he went to our class's chem blog.

Mr. H went over Hannah's and Neil's blog posts and then gave a few tips on how to make both blogs a bit better for next time.

Mr. H then had the class open up their chemistry packets to the last page to look over today's lab, which was MM6 Conservation of Mass Lab. As the class wrote down the purpose, he explained what we were going to do in today's lab and what to expect. He told the class that since we were going to be dealing with liquids and chemical reactions, that we should wear our safety glasses. He explained to us that we were to find the mass of a flask before the chemical reaction and after, and then compare the differences.

As everone went to their lab stations, they first began by pouring a blue liquid into a flask and then put a testing tube filled with a white substance. Groups then went and measured the flask with all its components as shown below. 

Click to view video.

Groups then returned the their stations, recorded the mass, and then put a cap over the flask, flipped over the flask, and saw the chemical reaction between the white substance and the blue liquid. The result of the chemical reaction was a white solid that formed. Groups then went on to find the mass of the flask with all its components and record their results.

When students finished, they went back to their desks and Mr. H began to pass out scan-trons for our pop quiz. The quiz was only 14 questions, and consisted of the material learned in chapters 1:1-2. The quiz lasted untill the end of class.

Monday, September 13

We started class today with Mr. Henderson telling us to get out our calculators, lab notebooks, packet, and to make sure we had patience. We began class by reviewing Lab MM6, the Conservation of Mass Lab. During this lab, we measured the mass of chemicals before and after a chemical reaction. The purpose was to figure out if mass was retained or changed during a chemical change. One person from each lab group went to the front of the room to record their data so we could see what the overall data of the entire class was. This is what the class data turned out be:

We then discussed whether or not the results of the lab shows that mass is retained during a chemical change. Some people said that mass was lost, since some of the masses decreased lightly. Others said that the mass stayed the same because it only changed slightly. Mr. Henderson told us that the mass had stayed the same. He said that in chemistry, 157.37=157.21. This could be because of the uncertainty or some of the chemicals may have fallen out when it was measured for the second time.

Once we finished reviewing the lab, we started to learn about metric conversions. We were told we had to memorize four of the prefixes. We learned a great way to remember them.

1 kilometer=1000 meter

100 centimeters= 1 meter

1000 millimeters=1 meter

10^9 (1,000,000,000) nanometers=1 meter

We also learned a way to remember the many different prefixes by using a scale.

We learened how to use this scale to do metric conversions. If you wanted to convert a kilometer to a meter, you move the decimal place 3 places to the right since the base unit is 3 spaces to the right of the kilo. If you wanted to convert millimeters to meters, you move the decimal place 3 places to the left since the base unit is 3 units to the left of the milli. We practiced doing this by doing a worksheet, page 7 in the packet.

We then went over problems 7 and 8 form the worksheet. 7 was converting 1 mL to kL. First we learned to convert it to L. If you move the decimal place 3 to the left, you get 0.001 L. If you move that 3 more places to the left, you get 0.000001 kL. for 8, the problem was to convert 1.0 Mg to mg. Mg was not on the scale, but it was listed on the worksheet as 10^6. If you calculate 1.0 X 10^6, you get 1,000,000 g. It still needs to be put into mg from g, so you move the decimal place 3 spaces to the right. The solution to that is 1,000,000,000 mg (10^9 mg).

We finished class by being assigned our homework to do a Webassign reading sheet for tomorrow and our Delicious Assignment, which is due on Friday. Overall, it was a very productive class.

Tuesday, September 7

Today in Chemistry, we mainly focused on measurements. We began the class by reviewing the assignments. Mr. Henderson reiterated that Labs 1-4 and packet pages 3 and 4 are due tomorrow, Wednesday September 9; and the Intro to Measurement Lab is due on Wednesday. He then proceeded to discuss the lab from yesterday, the MM4 Separating Mixtures Lab. He used a similar (example) lab about coins to demonstrate how to find the percent composition of each element in a mixture. First it is needed to find the total mass of the mixture, and then the mass of the element whose composition you wish to find. Then, you divide the mass of the element by the total mass, and you have the percent composition of that element. Mr. Henderson multiplied the number present of each coin by the mass of that type of coin, then divided the total mass of the coin mixture to find the percent of coins which make up the mixture. He then gave us time to This link describes how to find the percent composition:
http://www.chem.tamu.edu/class/majors/tutorialnotefiles/percentcomp.htm


Next, we began the Intro to Mixtures lab, which taught us about the precision of different instrument (with some divisions), and a graduate (with many divisions). Then we had to measure the length of a blue pen with multiple rulers that had various degrees of divisions. Through these two experiments, we found out that the instruments with less divisions force you to estimate more, and therefore be less precise. After that, we weighed the mass of a penny using three different mass balances, which gave slightly varying numbers. We then discussed significant digits, which are important when communicating the precision of our measurements. Mr. Henderson stated that in regards to significant figures, one figure is one that is always estimated. In other words, it can be assumed that all of the digits are exact up until the last one (and it is important to do this when measuring something yourself in order to communicate it to others).
This link is very helpful in understanding the concept of the degree of uncertainty:
http://www.tutorvista.com/content/chemistry/chemistry-iii/chemistry-concepts/uncertainty-measurement.php

^^These are the different instruments we used to measure the volume of water.

Mr. Henderson today emphasized the importance of the difference between mass and weight. He clarified that mass is the amount of matter one object has, and gravity is the force which acts on that amount of matter. He gave the example that if a person were to go to outer space, they would have a different weight (because different planets have different amounts of gravity), but his/her mass would remain the same. He also pointed out that our scales in Chemistry calculate mass, whereas typical scales calculate weight.
This is a really good link that describes the difference between mass and weight:
http://www.colorado.edu/physics/2000/periodic_table/mass.html

Overall, today was a very informative day in Chemistry; and we learned much about measurements. Don't foget about the pop quiz on Friday!