30 Alum Crystals Facts: Curious Details Revealed On This Chemical Compound

Potassium alum, or potassium aluminum sulfate, is a natural salt that has a number of applications.

Although there are various other types of alums, potassium alum is the only edible compound among the lot. It is approved by the FDA as a generally recognized safe (GRAS) substance.

Alum is usually found in a colorless or translucent crystalline form. You can easily spot a jar of the stuff on the spice rack of your grocery store.

The packaged aluminum sulfate at stores would be small crystals, which you can grow into a large crystal resembling a diamond.

Of course, it would take a little time, effort and patience, but alum crystals are pretty easy to grow. If you have access to other alums and take the necessary safety precautions, you could also experiment with growing other types of alum crystals!

Alum Crystals Composition

Alum is a common name that is used to refer to potassium aluminum sulfate, as well as other aluminum sulfate compounds like chrome alum.

• Potash alum is also known as a 'double sulfate' because it contains two cations - potassium and aluminium.
• Alum has the chemical formula KAl(SO4)2.12H2O and is comprised of potassium, aluminium and sulfur.
• This salt is sourced from two minerals - the sulfate alunite and the ore, bauxite. Bauxite is the world's primary source of aluminum!
• Alums such as potassium sulfate, sodium and ammonium alum are produced industrially.
• The chemical properties of alum causes it to turn into octahedral crystal form in neutral solutions, and cubic crystal form in alkaline solutions.
• Alum crystals can be grown by saturating alum powder in a container of hot water. This mixture should be left to rest overnight covered by a patch of filter paper.
• If you pour out the excess water, small crystals will be found at the bottom. These crystals are called seed crystals. A seed crystal is what you would use to grow a bigger alum crystal.
• All you have to do at this point is tie a nylon string around the best-shaped seed crystal and suspend it in the alum solution, covered by the filter paper. Make sure your crystal doesn't touch the bottom or sides, and scrape off any competitor crystals that grow on the sides. Grow it until you are happy with your crystal!

The Uses Of Alum Crystals

Alum crystals are used for a variety of purposes, ranging from tanning to dyeing to medication. Read on to discover some of the uses of different alum crystals, especially the widely used potassium alum.

• Wet alum crystals are used as deodorants to prevent unwanted body odors. This is done because potassium aluminum sulfate contains antibacterial properties. However, it is inadvisable to apply alum on freshly shaven or sensitive skin as this can cause irritation.
• Alum is used as a home remedy for a range of ailments. For example, canker sores or oral ulcers are treated at home by applying alum. Crystals can be crushed to make alum powder for this purpose.
• In the U.S., it is widely used for edible purposes, such as pickling. Although alum is a non-toxic preservative, it is dangerous when ingested in large quantities.
• Potash alum is also used as an acidic leavener in baking powder, such as Youtiao, a traditional Chinese bread.
• Potassium and ammonium alums are used as flame retardants in the production of clothing, wood, and paper materials.
• Certain homemade recipes for playdough or clay meant for modeling by children have alum as an ingredient.
• Traditionally, Japanese artists have dissolved alum and animal glue to make a solution that would be used as an undercoat for paper.
• Chrome alum used as a hardener in the gelatine emulsions of photographic film!

Types Of Alum

There are a few different types of alum. The edible kind which is commonly available in stores is potassium alum. Apart from potassium alum, there exists sodium, ammonium, selenium, and chrome alum.

• Sodium alum, or soda alum, is what we commonly call baking powder. The chemical formula of soda alum is NaAl(S O4)2·12H2O, and it acts as an acidulant in food, adding a sour or tart flavor to it.
• Ammonium alum is used for a variety of purposes such as tanning, dyeing textiles, and making vegetable glue, as well as several of the same purposes that you would use potassium alum or soda alum for. The chemical formula of ammonium alum is N4Al(SO4)2·12H2O.
• Chrome alum, or chromium aluminum sulfate, is a chemical compound that has a deep violet pigmentation. It has the chemical formula KCr(SO4)2·12H2O.
• A fascinating use of chrome alum is for making violet or lavender crystals in other alums.
• Chrome alum used to be a preferred tool for the tanning of leather, however, a more effective chemical compound is used today.
• Selenate alums have the chemical formula SeO4 to the power of 2-. This alum is formed when selenium takes the place of sulfur during a chemical reaction. As a result, you get a selenate instead of a sulfate.
• Aluminum sulfate, although not technically an alum, is known as Filter Alum or Papermaker's Alum. This is because it is used in the purification of water.

The Physical Features Of Alum Crystals

Different types of alums have different physical properties, such as solubility in liquid due to the differences in their chemistry. Have a look at some of the physical features of potash alums below.

• Potash alum crystals ideally have an octahedral structure and are almost colorless when in solid form. Alum crystals dissolve easily in liquid and turn into a red, porous mass called 'burnt alum' when heated.
• Powdered alum has a melting point of 198.5 degrees F (92.5 degrees C) and a boiling point of 392 degrees F (200 degrees C ).
• At high temperatures, alum solution evaporates and releases sulfuric acid. A mixture of alumina and potassium sulfate is left behind after this.
• When heated to the extreme temperature of 197.6 degrees F (92 degrees C), alum fuses in its own crystallization solution.
• When dissolved in an aqueous solution, alum displays all of the chemical properties of its constituent elements.
• Chrome alum, in an aqueous solution, appears dark violet. However, it turns dark green when heated to a temperature of 122 degrees F (50 degrees C).
• Among the alums, sodium alum is the most soluble, and alums like rubidium are barely soluble in water.