Last night a friend came over and we tried to set up an ammonia fountain. We are both working on improving our working knowledge of chemistry – and the ammonia fountain is a good project to practice a bunch of basic labs skills. It is also fun to watch.
I didn’t have any Phenolphthalein, so my partner in crime/chemistry suggested that we use the juice from boiled red cabbage as our PH indicator. The cabbiage contains an anthocyanis (flavins) pigment. You just boil the sliced up cabbage for about a half hour – then drain off the now purple fluid. That fluid changes to either red or green depending on PH of material added to it. Both of us were surprised at how well the homemade indicator worked.
Where things kind of went off the rails was with our seals. I don’t have much in the way of chemistry equipment yet – so I am making or buying what I need for each experiment. We started the day cutting and bending sections of gas tubing for connecting the different vessels together. I then drilled out solid rubber stoppers to the appropriate size to snuggly fit the tubes. While I need to get something hotter than a butane torch so it does not take forever, hot working the glass was fun.
The problem came from out inter-tube connections. To make it easier to un-stopper and re-stopper we used latex surgical tubing to connect the glass pipes. The NH3 glass will eat away at the latex, but at a slow enough rate I was not worried about it for this experiment. We used clothes pins as low pressure release seals on the surgical tube. Our problem was that the inner diameter of the tubing was too large, and even with tape over the ends we never got a good enough seal. This first attempt at an ammonia fountain did go off – however while it started to fountain PH indicator, which changes color in the presence of gaseous NH3, the poor seal quality quickly let enough air into the system that it kills the pressure difference which drives the fountain.
In the picture you can see the heated flask where we were off gassing NH3 connected to our inverted flask used to catch the lighter than air NH3 gas. Once the inverted flask is full of NH3 gas, we remove the feed tube, then re-stopper the inverted flask connecting it to the flask full of PH indicator. Squeezing the dropper injects some water into the inverted flask, water that absorbs the NH3 creating a partial vacuum in the flask, which in turn draws the PH indicator up the tube creating the fountain. The indicator has the fluid change color when it enters the inverted flask.
All in all a fun day, we just need to re-do the experiment once I buy a few things. We will probably use a larger flask as well. A 250mL boiling flask just does not have enough volume to look impressive once the fountain gets going. Still, this already looks like a great experiment to do in teaching science to kids. Because of the ammonia gas I am going to hold off at least another year before trying it with my nephew – but this one is definitely going in the rotation. The color change and the fountain look like magic.