Flying on baking powder

You don’t always need a big laboratory for exciting experiments... And you can launch a rocket easily using just baking powder.

The Scottish island of Scarp is possibly the most isolated corner of the United Kingdom. A 750-metre-wide strait separates the island from North Harris in the Outer Hebrides. Then it’s more than seventy kilometres over unsealed roads to the fishing village of Stornoway, where a three-hour ferry trip will take you to Ullapool on the mainland. Which is itself in the middle of nowhere.

The island is so remote that it used to be inaccessible for weeks, or even months. This had to change, the British decided in the early 1930s. Wouldn’t it be nice if the post were always delivered on time, regardless of the weather conditions? And so the island became world famous among philatelists, space flight experts and fans of loud explosions.

In 1934 the British government was approached by the German inventor and charlatan Gerhard Zucker, who claimed that he could deliver the post from and to the island by rocket. The 31^st of July of that year was the big day; on the beach of Scarp, in front of a crowd of dignitaries, Zucker lit the fuse of his rocket which was filled with 1200 letters and postcards. Eyewitnesses described the following events as ‘a flash of light, a huge cloud of smoke and a confetti rain of singed post that settled over the beach.’

Almost 75 years later, rocket technology has hardly progressed. Roughly speaking, a rocket still consists of a large cargo of highly flammable material that is ignited under controlled conditions. The combustion creates gases, which are under pressure, and if you control the release of these in one direction the rocket will move.

You can try this at home too, but – for your own safety and that of others – without using highly flammable fuel. The Cogito ergo boom! rocket is filled with baking powder, vinegar and a small piece of a paper towel or toilet paper. During the reaction between baking powder (sodium bicarbonate, NaHCO₃) and vinegar (a solution of acetic acid, CH₃COOH), carbon dioxide gas is produced, and if you let the reaction happen in a closed container you will build up enough pressure to launch a small rocket. You can find the chemical equation in the previous episode of this series.

For this experiment you need an empty photo film container (ask at a photography shop). Fold up a teaspoon of baking powder in a piece of paper towel and stuff it into the container. The paper towel is used to slow down the reaction so that the contents do not immediately start fizzing when you add the vinegar. Pour (outside!) a dash of vinegar into the container, put the lid on and place it upside down on the ground. After a while the pressure in the container will build up to the point that the lid will be forced off with a loud plopping sound, shooting the container into the air. The container should shoot five to six metres into the air. The paper filled with baking powder will be enough for several launches.

The amount of gas produced in the reaction can easily be calculated. Let’s say that two grams of baking powder reacts with the vinegar; that is about 0.02 mol (mol is the unit for the number of molecules). Because 1 mol of baking powder produces 1 mol of CO₂ in this reaction, that means that 0.02 mol of gas is produced. At a temperature of 25 degrees Celsius a gas has a volume of 2.45 x 10-2 m3 mol-1. That means you will get 0.02 x 2.45 x 10-2 x 103 = 0.49 litres of CO₂. In comparison, a photo film container has a volume of about 35 millilitres.

Of course, the big question is whether you can carry out this experiment on a larger scale. The editors’ attempt to launch an empty Pringles can failed, because the can could not be completely sealed.

Any tips for a better large container are welcome!

Author: Ernst Arbouw