Category → IYC 2011
It’s time for another edition of Sidechain’s favorite chem demos. The one I’ll be describing today holds a place near and dear to my heart. When I was a young high schooler (a shorter polypeptide… get it?), my high school chem teacher showed this to our class. She had a glass of what looked like water. She poured it into a wine goblet, and the water turned to wine (cool, right!). She then poured the ‘wine’ into another glass, where it became ‘milk’, which when poured into the final glass turned into ‘beer.’ When I first saw this, I really thought it was magic. It turns out that the chemical principles are pretty simple! All the student really needs to understand is acid-base chemistry, indicators, and precipitates. Anyway, here’s what you’ll need:
- Glass #1: 0.1 M Sodium Carbonate (NaHCO3). What I did was make 100mL of a stock solution and add around 50mL to a clear water glass.
- Glass/Goblet #2: A few drops of phenophtalein in the bottom of a long-necked wine glass. I usually use a plastic one and put some tape on the bottom to cover the indicator solution.
- Glass #3: 5mL 1.0M BaCl in the bottom of a clear glass with some tape on the bottom.
- Glass #4: 5mL 12M HCl and 5mL of bromothymol blue indicator, at the bottom of a pint glass/plastic clear solo cup
So if you can’t guess, the science behind this is pretty simple.
- Sodium Carbonate is a basic solution that looks like water
- Adding phenothalein will make the solution purple, and look like wine
- Adding Barium ions will precipitate out a suspension of Ba(OH)2, which will look like an opaque white liquid (milk!)
- In the last cup, the concentrated acid will (a) acidify the remaining base, eliminating the Ba(OH) (b) result in the evolution of CO2 gas and (c) make a beer-like color with the indicator
This demonstration is pretty easy to explain to a group of first-year chemists, and is a great application of the skills they have already learned! Just remember not to drink any of these liquids, especially the “beer” (no matter how tempting it may be!)
Posted on behalf of Charles Michael Drain, chemistry professor at Hunter College
As part of the celebration of the International Year of Chemistry, graduate student Jacopo Samson from Hunter College of the City University of New York and I participated in the “pH of the Planet” experiment with over 250 seventh grade students from Readington Middle School in Hunterdon County, N. J.
During the last week of April, the students brought in water samples from wells, lakes, rivers, and streams. After viewing a National Geographic video about water on YouTube and discussing the properties of water, students worked in pairs to observe the turbidity and use indicators to determine the pH of 3-4 samples. Seventh grade science teachers Gerry Slattery and Chip Shepherd helped plan the experiment and worked with students when they had questions. A couple of students then tabulated the data and determined the average for each water source. Both the students and I were impressed that their averages matched well with what we determined using a calibrated pH electrode. The tabulated data is being uploaded to a database along with pH values of local water sources determined by students from every part of the planet.
“I didn’t realize how many people don’t have access to clean water and how important pH is,” seventh grader Zach said.
Outreach is becoming one of the most important aspects of undergraduate, graduate, and professional chemistry. Reaching out to kids at a young age and helping them get in to chemistry is a priority. This is also one of the main focuses of the ACS’s International Year of Chemistry (IYC) 2011.
I remember in my first chemistry class when my teacher showed us the classic demo where she turned water to wine, then wine to milk, then the milk to beer. To me and my classmates, it seemed like magic. It was pretty much the coolest thing since, well, the power rangers. Or the Offspring. Anyway, we now have a much different perspective. These chemistry demonstrations utilize relatively simple chemistry to produce really fun and exciting results. Does that mean that all the magic is gone? I don’t think so. A few weeks ago, I had the chance to do some of these demos to a crowded audience of elementary school kids. Needless to say, I had a blast. The kids did too. Over the next couple weeks, I’m going to be profiling a couple of the demos I did, and how to do them for your friends, neighbors, or chemistry classes. We all know that chemistry is fun: other people just need some help remembering.
Today, I’m profiling one of my favorites: The elephant’s toothpaste. Here’s how it’s done:
What you need:
- One (1) Graduated cylinder, as large as you can find it. Really, the bigger the better. I used a 2.o L guy I found lying around in my lab, but I imagine that doing this with a 4 L or 8 L would make some kid’s day.
- 150 mL of dish soap. Really doesn’t matter what kind
- 150 mL 30% Hydrogen Peroxide. This is dangerous – it’s an irritant and will hurt if you get it on you. Wear gloves, a lab coat, and goggles.
- Food coloring (be very generous)
- ~5mL of saturated KI. I do this by putting a lot of KI into a 50mL falcon tube and adding water. Then I shake until I’ve dissolved all I can, and add 5mL
This is how it’s done:
- Put the peroxide, soap, and food coloring (again, be generous)
- Add some KI
- Watch it happen
This demo is really fun. Just don’t forget to lay down some newspaper so cleanup is a easier. Also, a note about safety: because of the peroxide, don’t be staring down the tube as you pour the KI in. First, you’ll get burned by peroxide, then you’ll get majorly stained by KI. Neither of these things will be enjoyable, I promise. If you’re prepared correctly and introduced the demo in a fun and interesting way, this should go off great and be a highlight of your chemistry show! Enjoy!
P.S: The recipe above is optimized for a 2 L graduated cylinder. If you want to use bigger or smaller, scale up or down respectively.