Regular readers of this website will know that I am a fan of using materials readily available in supermarkets, for example beer bottle caps in the determination of the formula of magnesium oxide. I have now added another kind of shop - toy shops. Recently I came across a diving submarine for GBP4 in a toy shop in Cardiff. To get it to work all you need to do is add baking powder and immerse the submarine in water. I took it with me to an InThinking workshop for chemistry teachers new to the IB that I ran in Berlin a few days ago and it was a big hit. I used it as an example of a possible design experiment. There are about 20 tried and tested suggestions in the usual list of possible design investigations so I thought it would make a change to investigate something a bit more interesting. The key to any successful design experiment is to pose a problem with many different variables so that each student ends up with a different research question. On the diving submarine packaging there is some useful background information on how it works.

“The submarine sinks naturally because it is heavier than water. However, when the water comes into contact with the baking powder, carbon dioxide is released and the rest of the gas causes the submarine to surface. When all the carbon dioxide from one reaction has been released from the submarine (you will see bubbles coming out of the submarine) the sub then ‘dives’ once again. This process will be repeated until the amount of baking powder left in the chamber has reduced to such a level that the volume of carbon dioxide produced is not enough to raise the submarine again until the chamber has been re-filled.”

So give your students “Investigate an aspect of the diving submarine” and see what they come up with. Here are just ten of the variables that the teachers in Berlin listed.

• Time for the submarine to rise to the surface

• Type of baking powder used (all contain sodium hydrogen carbonate but some then contain cream of tartar whereas others contain disodium diphosphate etc.)
• Temperature of the water
• Depth of the water
• Mass of ‘fuel’ (baking powder used)
• Mass of submarine (this could be varied by adding plasticine etc.)
• Length of intervals between successive dives
• Salinity of the water used
• Depth of the water
• The pH of the ‘water’

Clearly there are many variables from which students can select an independent variable, a dependent variable and then think about how they can control all the other variables to design an experiment to fit their particular investigation. And they can have fun at the same time!