SGChem1 Post #2

This week in SGChem1, we reflected on the Mass and Change Lab. We got into our groups and worked on whiteboards to try and figure out what happened during the remainder of the stations in the lab. Here are some examples:


We did one experiment with Alka Seltzer where we massed the Alka Seltzer and some water, then dropped the Alka Seltzer into the water. The solution lost half of a gram.
From this experiment I concluded that when the Alka Seltzer dissolved into the water, some of its particles became lighter than the water particles and they rose out of the water and into the air. That's my theory. I still wonder why not all of the Alka Seltzer particles rose, and why the mass didn't have a greater change.

The next experiment we reflected on was the Calcium Chloride/Sodium Carbonate station.

In our group, we mixed the two chemicals and the solution lost 11.7 grams. We later learned that that was because we didn't mass the vials. Most of the rest of the class's mass didn't change, though. So we can assume that not much happened when we mixed the two chemicals. Some of the other boards did show that some kind of reaction happened and part of the solution became denser and sunk to the bottom of the vial. So maybe the Calcium Chloride particles bonded with the Sodium Carbonate chemicals. Our group would have to retry the experiment to get sufficient results.

And the last experiment we reflected on this week was the one where we burned steel wool. This experiment confused all of us, because you wouldn't expect something to gain mass after it's burned. But we suspect that when we burned the wool, a chemical reaction occurred, creating new particles with a bigger mass. Our wool gained 0.2 grams.

I learned from the Mass and Change Lab that the mass of something before and after an event occurs cannot easily be predicted. It takes experimentation and questions to find answers.

Besides that, the main ideas from this weak were mostly along the lines of measurements. We learned about valid measurements. A measurement should have one estimated digit. The estimated digit should be the last digit in the measurement. The estimated digit should correspond to one tenth of the smalls marks. For example, if you're using a ruler with only centimeter marks, and you're measuring a wooden block, the measurement of the block should have two digits. So instead of writing 3 centimeters as the measurement, you would get more specific and write 3.0 centimeters. This brings us to significant digits.
If a measurement is recorded properly, all the certain digits and one estimated digit are called significant digits. There are 5 rules to significant digits.
1) All non-zero numbers are significant. (significant digits are underlined)
Ex. 3200
2) Sandwiched zeros are significant.
Ex. 0.405
3) Zeros that are only placeholders for a decimal are not significant.
Ex. .093

4) Zeros at the end of a number that also contains a decimal are significant.

Ex. 20.20

5) Exact numbers may be thought of as having an infinite number of significant digits.

Ex. 15

Significant zeroes and significant numbers are helpful because they relate to measuring. If you are measuring the mass of something, you want to get as specific as you can. If something weighs 154.3 grams, you don't want to record its measurement as 150 grams. That only has two significant digits. You want as many significant digits as possible. Everything we learned this week comes back to measurement and making work in Chemistry a little easier.