Potassium and water
Put a lump of potassium in a dish of water and it will give off a pinkish light, get very hot and skim across the surface at speed. A favourite experiment of many science classrooms, potassium is a highly reactive metal that reacts violently in the presence of oxygen and water. It forms potassium hydroxide (KOH) and hydrogen gas (H2). Potassium atoms have 19 electrons – one of which is alone in an outer shell.
This makes potassium very keen to lose an electron so it has a complete outer shell and is more stable. When the reaction begins, enough heat is given off to ignite the hydrogen gas, which then reacts with oxygen to produce water. Potassium is so reactive that it must be stored in kerosene, so as not to come into contact with water vapour in the air. Even oxygen in the air is enough to cause potassium to spontaneously combust! Because potassium is so reactive, it’s not found in its elemental form, but is common as a compound.
Potassium chlorate and Jelly Babies
Watching a Jelly Baby meet its demise at the hands of potassium chlorate is a spectacular affair. There’s an abundance of energy inside Jelly Babies stored as sugar, released in intense flames and a piercing scream when potassium chlorate is added to the mix.
Potassium chlorate is a powerful oxidiser, taking its form as a white powder and commonly used in fireworks and explosives. The ‘ate’ part of chlorate describes the oxygen atoms attached to the chlorine atom, and the chemical formula is KClO3. Chlorate-based oxides are more efficient oxidisers than those in gunpowder and potassium chlorate needs to be handled very carefully due to its unpredictable ability to spontaneously ignite.
The reaction happens when a small amount of potassium chlorate is placed in a test tube and heated until it becomes a clear liquid. Needless to say, safety screens and goggles are a must. The Jelly Baby is placed with tongs into the tube and instantly produces lively flames, intense screaming and plenty of smoke. The reaction can last up to 20 seconds and gives off noxious fumes so ventilation is also needed.
Potassium nitrate and sugar
There’s something strangely satisfying about witnessing the volatile display of smoke, colour and fire given off by the mixture of potassium nitrate, sugar and heat. The amount of fire varies, but there is always an abundance of smoke. You have most likely seen this reaction at a firework display, or from the smoke stunt planes deploy where coloured dyes are often added for effect.
Potassium nitrate (KNO3)- aka saltpetre – is an essential in any pyrotechnics cookbook; it’s one of the main ingredients in gunpowder, for example. Potassium nitrate works as an oxidiser, giving off oxygen and promoting the burning of fuel.
As seen in the ‘Screaming Jelly Baby’, sugar is an extremely effective fuel; it contains energy that ‘burns’ in our bodies and converts to useful energy we use to perform any physical activity. When heat is applied to saltpetre and sugar, the saltpetre loses an oxygen atom – transitioning from KNO3 to KNO2 and oxidising the sugar. The sugar burns, releasing smoke which rapidly expands and can generate enough thrust to lift a small rocket.
Interestingly there’s a programme called Sugar Shot to Space that aims – as you would probably guess – to launch a rocket powered by sugar propellant alone beyond Earth’s atmosphere.