This is a very memorable demonstration and it’s well worth doing if you can get hold of dry ice. The film does include some ideas about how to obtain dry ice but if all else fails try searching on the internet for dry ice cleaning companies local to you. Of course, having got your dry ice, you’ll be able to do lots of other activities with it too and with several other classes: its sheer memorability makes it worth the money.
Before carrying out the demo as shown here, it is recommended that a very small amount of dry ice is placed on benches so that students can literally watch it “disappear” in front of their eyes. Warn students not to hold it though as it will burn their skin and be particularly careful that it can’t fall into their laps. You might want to introduce students to the concept of sublimation and explain that carbon dioxide is one of very few chemicals that turns directly from a solid into a gas without going through the liquid phase.
Instead of carrying this out as a large scale demonstration, it is perfectly possible for students, perhaps working in pairs, to prepare solutions themselves that are just alkaline (ie the indicator has only just turned purple) using 250cm3 beakers. The teacher can then walk around the classroom dispensing the dry ice directly into each beaker.