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.

SG Chem Post #1💯

We started off SG Chem with a pompon activity. It involved a tube and four pompons. It looks like this:

Whenever one pompom was pulled down, you could pull any pompom and the hanging pompom would rise. For example, if the green pompom was hanging down, you could pull the yellow, blue, or red pompom and the green one would get pulled back to the tube. 

In our groups, we wrote on whiteboards what we thought was going on inside the tube. Our group thought that the yellow and blue pompoms were connected, and the green and red were connected. The string we thought connected the yellow and blue pompoms would loop around the green and red string once in the middle. That way, pulling on any pompom could potentially affect any of the other pompoms.

When Dr. Finnan pulled apart the tube, no strings were connected. My theory is that he used magnets. Instead of the two strings looping around each other, the two strings each had three ends; two connected to the two pompoms and one with a magnet on the end. When you're pulling on the pompoms, the magnets often come together in the middle, but when Dr. Finnan pulled apart the tube, they had been separated. That was a cool intro to Chemistry.

Next was the flaming paint can. Dr. Finnan filled a paint can with methane. The can had two holes in it: one on the top, and one on the side. Right after filling the can, he covered the holes with tape, and set it down in the middle of the room. Next, he removed the tape, and lit the methane coming out of the top of the can. The fire went for a while, and after a minute or two, the can exploded and the cap flew off. Here's a video:

In our groups on our whiteboards, we drew what we thought the particles looked like before and after the explosion. We explained how the can was filled with methane at first, then right before the explosion it was filled with a mix of oxygen and methane, and then after the explosion the can is filled with oxygen because the methane, which is lighter than air, rises out of the can. This is pretty much what everyone else thought, too. 

Our most recent experiment was a mass experiment. It had six stations. At the first station, we documented the mass of a piece of steel wool before and after we pulled it apart. The steel wool lost 0.2 grams, but that was only because we lost some of the material while we pulled it apart. Here's a diagram of what happened:

At station number 2, we measured the mass of steel wool, held it over a torch until it was red hot, and then measured the mass again. The wool gained half a gram, so, apparently, when you burn certain materials, they gain mass instead of lose it.

At station 3, we weighed a piece of ice before and after melting it. It lost .1 grams, which is essentially nothing. We kept the ice in one container, and all it did was melt, losing no mass, so it makes sense that the weight stayed virtually the same.

The fourth station was a chemical reaction station. We weighed two chemicals, Na2CO3, and CaCl2, and their total mass was 41.3 grams, together. Then we combined them into one solution and weighed that, and it lost 11.7 grams. Something in the reaction of those two chemicals must've caused the solution to lose weight.

We dissolved sugar at station five, weighing it before and after. It lost no mass, which makes sense because you aren't really losing anything by dissolving.

At the sixth and final station, we dissolved an Alka Seltzer tablet in water and weighed it before and after. Surprisingly, it lost a whole gram. This is puzzling because of the previous station, where dissolution caused the sugar solution to lose nothing.

In conclusion, we learned to be careful with our experiments, and that mass isn't always what you expect.