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Tuesday, March 8, 2016

The One Where We Launch Even More Rockets (And Talk About Ovens)

"Reactions As Recipes"

Practice Problems:

     This cycle's practice problems were the most challenging ones so far. While the first few (with an excess reactant) were easy enough to understand, the other problems we did later were more confusing. Because there were so many different parts to the problem that I could (and did) mess up on, I struggled with these problems more than previous sets. My biggest problem was that I had no idea that every number in the "C" row had to be multiplied by the reference ratio. I also kept on making a bunch of simple mistakes, which included getting the wrong molar mass of substances with multiple elements and rounding wrong.
Ex. of Understood Problems
If 0.25 moles of sodium metal, Na react completely with excess oxygen, O2 gas how many moles of solid sodium oxide, Na2O are produced?
Ex. of Challenging Problems
How many liters of hydrogen gas must react with 4.0 grams of nitrogen gas to produce to produce ammonia gas, NH3 with no excess? Assume STP (1 atm and 0oC)

    One of our first activities involved making a mini version of our hydrogen rockets. We had smaller bottles filled with some water. After pouring in a bit of calcium carbide, we capped the bottle with a bandana. The reaction between the water and calcium carbide produced acetylene gas. We could prove this by lighting the bottle, and the small explosion that occurred after showed that the oxygen from the environment reacted with the newly formed acetylene gas .

Our two best mini rocket explosions

     Another activity we did was observe the reaction between potassium nitrate, sucrose, and fire in a "smoke bomb". This reaction creates carbon, the black substance left behind in the jar. 

A slightly sped-up clip of the smoke bomb

     We also placed a piece of magnesium in some hydrogen chloride to learn how to use the ideal gas law equation in stoichiometry. This lab taught us the difference between "limited" and "excess" reactants.
During the reaction, the magnesium in the test tube got warm enough to form steam.

     In an "enlightening" demo that involved dry ice and magnesium, we got to see another reaction that formed carbon. The magnesium was placed in a small hole carved in the dry ice then lit. An extremely bright light shone as we covered the magnesium with another block of dry ice. After we uncovered the magnesium, we found that carbon was formed! Mr. M applied this reaction to global warming, stating that this is one of the possible (albeit insanely expensive) ways to get rid of excess carbon dioxide in the atmosphere.

Two trials of the demo mentioned above, (one in the light, another in the dark)

     As another demo for this cycle, Mr. M made another rocket. However, this one relied on baking soda and vinegar to launch (yes, like the cliche middle school volcano science fair projects). This demo was done to reinforce the process we learned to treat "reactions as recipes" (the problem this demo represented is on the white board in the right of the video).
A brief slow-motion clip of the coke bottle-pens-baking soda-vinegar rocket

     Our final lab for this cycle involved us using 9-volt batteries to ignite steel wool. After burning the steel wool, we left it over the weekend and then poured water over it when we came back. The white iron oxide that formed when we burned the steel wool then turned red when we got it wet, which demonstrated a faster way of forming rust.

A few short clips of the rusting activity

Quiz (To Be Edited After We Get Tests Back):
     The quiz for this cycle wasn't devastatingly difficult, but I did get paranoid while solving the problems on it because of the numerous areas you could make simple mistakes in. The blimp question was especially daunting because of the huge numbers involved since we had only done problems with fairly small numbers before the test. In the end, this was probably the cycle test I spent the most time on, but I still feel confident in what I turned in.

  • Does the technique for solving these types of problems change greatly when more than two reactants are present? Do those problems even exist? 

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