2019 has been declared by UNESCO as the Year of the Periodic Table. To celebrate, we are releasing a series of blogs about our favourite elements and their importance to the chemical industry. Today’s blog is about iodine and some of the exciting reactions it can do!
Iodine & Aluminium
Reaction between iodine and aluminum. These two components were mixed together, followed by a few drops of hot water. Source: FaceOfChemistry
Reactions between iodine and group 2 metals generally produce a metal iodide. The reaction that occurs is:
2Al(s) + 3I2(s) → Al2I6(s)
Freshly prepared aluminium iodide reacts vigorously with water, particularly if its hot, releasing fumes of hydrogen iodide. The purple colour is given by residual iodine vapours.
Iodine & Zinc
Zinc and iodine react similarly to aluminium and iodine. Source: koen2all
Zinc is another metal, and when it reacts with iodine it too forms a salt – zinc iodide. The reaction is as follows:
Zn + I2→ ZnI2
The reaction is highly exothermic, so we see sublimation of some of the iodide and purple vapours, as with the aluminium reaction. Zinc iodide has uses in industrial radiography and electron microscopy.
Iodine & Sodium
Iodine reacting with molten sodium gives an explosive reaction that resembles fireworks. Source: Bunsen Burns
As with the other two metals, sodium reacts violently with iodine, producing clouds of purple sublimated iodine vapour and sodium iodide. The reaction proceeds as follows:
Na + I2→ 2NaI
Sodium iodide is used as a food supplement and reactant in organic chemistry.
Iodine Clock reaction
The iodine clock reaction – a classic chemical clock used to study kinetics. Source: koen2all
The reaction starts by adding a solution of potassium iodide, sodium thiosuphate and starch to a mixture of hydrogen peroxide and sulphuric acid. A set of two reactions then occur.
First, in a slow reaction, iodine is produced:
H2O2 + 2I− + 2H+ → I2 + 2H2O
This is followed by a second fast reaction, where iodine is converted to iodide by the thiosulphate ion:
2S2O32− + I2 → S4O62− + 2I−
The reaction changes colour to a dark blue or black.
The elephant’s toothpaste reaction is a favourite for chemistry outreach events. Source: koen2all
In this fun reaction, hydrogen peroxide is decomposed into hydrogen and oxygen, and catalysed by potassium iodide. When this reaction is mixed with washing-up liquid, the oxygen and hydrogen gas that is produced creates bubbles and the ‘elephant’s toothpaste’ effect.
There are lot’s of fun reactions to be done with iodine and the other halogens (fluorine, bromine, chlorine).
Iodine’s sublimation to a bright purple vapour makes it’s reactions visually pleasing, and great fun for outreach events and science classes.
2019 has been declared by UNESCO as the Year of the Periodic Table. To celebrate, we are releasing a series of blogs about our favourite elements and their importance to the chemical industry. Today’s blog is about the highly reactive gas, fluorine.
Fluorine wasn’t discovered until the 19th century, and even now very few chemists have seen elemental fluorine. Fluorite – fluorine’s source mineral – was used industrially as far back as the 16th century, but elemental fluorine wasn’t made until much later.
Fluorite is the mineral form of calcium fluoride (CaF2) and can be found in a wide variety of colours – from pastel free, to burgundy, and even purple or golden yellow. Many samples of fluorite can also be seen fluorescing under UV light. Fluorite’s main industrial use is as a source of hydrogen fluoride (HF), a highly reactive acid. It can also be used to lower the melting point of raw materials, such as steel.
Fluorite has been used in industry for hundreds of years and is fluorescent under UV light. Image: Pixabay
In 1886, French chemist Henri Moissan first made elemental fluorine by electrolysing a mixture of potassium fluoride and hydrogen fluoride. He later won the Nobel Prize in Chemistry for his work.
Large-scale production of fluorine first began during World War II, where it was used to separate uranium for the Manhattan Project – the United States’ nuclear weapons development project.
Fluorine is known for its high reactivity. It is the most electronegative element, which means it can react with almost every other element in the periodic table. Despite being difficult to handle, fluorine and fluorine containing compounds have many real-world applications.
Due to its reactivity, elemental fluorine must be handled with great care. Fluorine reacts with water to produce hydrogen fluoride, which is such a powerful acid it can eat through glassware.
Fluorine’s reactivity isn’t all bad – in fact, it has hundreds of applications. One of the most common uses of fluorine is the fluorides in toothpaste.
These fluorides exist usually as tin or sodium fluoride, and when you brush your teeth they react with calcium in the enamel to make it less soluble to acids. This gives some protection to your teeth from acidic foods such as fizzy drinks or juices.
The fluorochemical industry began in the 1930′s and 40′s with DuPont, who commercialised organofluorine compounds on a large scale. They developed Freon-12 (dichlorodifluoromethane) after General Motors showed chlorofluorcarbons (CFCs) could be used as refrigerants. The two companies joined together to market Freon-12, which quickly replaced previously used toxic kitchen refrigerants.
CFCs were found to be creating holes in the ozone layer, contributing to global warming. Image: Pixabay
CFCs were later banned by a number of countries due to the damage they caused to the ozone layer. More environmentally friendly fluorine-based alternatives are now used in refrigeration, including hydrochlorofluorocarbons (HCFCs) and hydrofluorocarbons (HFCs).
DuPont continued to pioneer the industry, when recently hired chemist Roy J Plunkett accidentally discovered polytetrafluoroethylene, also known as the polymer Teflon. Tests of the mysterious white polymer he had generated showed its’ high temperature stability and resistance against corrosion were significantly higher than any other plastic. It only took three years for large-scale production to begin.
Fluorine – Professor Martyn Poliakoff. Video: Periodic Videos
The development of Teflon lead to many other similar fluorine-containing polymers appearing on the market, including PTFE, which is used in breathable rainwear by the Gore-Tex business and was developed by Robert Gore, the son of ex-DuPont employee Bill Gore.
The fluorochemicals industry continues to grow to this day; in 2017 the global market was estimated at $17.6 billion.