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.