Today’s lab was a lot of fun, it was basically an ooohhh, aaahhh day. The lab, Six Types of Reactions, is from Ian Guch’s 24 Lessons that Rocked the World. We couldn’t do all six because some took me out of my comfort zone and I don’t have a fume hood in my kitchen. But Ian did recommend some other chemical reactions that we did instead and we watched some videos on youtube for the ones we didn’t do ourselves.
But before we started the labs I went over writing a lab report and asked the older students (juniors and seniors) to choose one of the labs we’d already done and try their hand at writing up a report for next week. I gave them this link to how to do a write up and an example lab report from Liberty High School. The procedure made me cringe a bit since every sentence begins with ‘The’, but I thought it was about right for a high school lab report. Purdue actually has an awesome website, including videos, on writing up lab reports but its way more than they need at this point.
For this lab, I set up 5 different experiments. The first one was a synthesis reaction where the students grabbed a SMALL piece (3 cm) of magnesium ribbon with test tube tongs and held it over a butane burner. The magnesium burns incredibly bright as it reacts with oxygen to form magnesium oxide, a fine white powder.
The second setup involved placing a small chunk of copper sulfate hydrate (dark blue) in a crucible and heating it up to drive out the water – this is an example of a decomposition reaction.
The third reaction was done as a demonstration because I only one piece of copper and very little silver nitrate. I made a 0.1 M solution of silver nitrate in a small centrifuge tube and place a piece of copper wire into the tube. This is an example of a single replacement reaction, the copper switches place with the silver and you end up with silver precipitate (solid) and the copper becomes copper nitrate (in solution). As you can see in the photo the copper wire grew silver fuzz! You can see a little bit of the copper wire sticking out of the solution.
We also did a double replacement reaction with the silver nitrate solution. For this one the students used a disposable pipette to drop the silver nitrate (0.1 M) into salt water (1M). The silver and sodium switch places forming silver chloride (solid) and sodium nitrate which remains in solution. The silver chloride forms a white precipitate immediately and slowly falls to the bottom of the beaker.
The fifth experiment was an acid-base reaction. Students used a disposable pipette to place 2 drops of sodium hydroxide (0.1 M NaOH) into a watch glass, then one drop of indicator which turned the NaOH bright pink. Then they dropped hydrochloric acid (0.1 M HCl) into the watch glass and the solution turns back to clear.
We didn’t do a combustion lab because two of the students had already demonstrated that reaction during the first lab back in September.
We also tried a decomposition lab from the home scientist CK01A Instruction Manual but we were not successful. This was one of the easiest labs, place baking soda in a beaker, place on hot plate to drive out the water. Water drops were supposed to form on the lip of the beaker but we never got any. We were also supposed to test for carbon dioxide inside the beaker but all those failed too. I’m not sure what went wrong, perhaps our hot plate wasn’t getting hot enough? Though I kind of doubt that since it felt like it was heating the whole room. But I did show the students how the cobalt chloride test paper turned pink when it touched water and would turn back to blue when it dried out.
Tyler Dewitt has a great video (as always) on major reaction types.
Here are some videos we watched in class on some reactions we did and some I wouldn’t do, like exploding hydrogen balloons.
This class was a lot of fun and I think I’l do some of these same reactions as demonstrations for the middle school students next week.