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Potash Alum

Last updated date: 17th May 2024
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What Is Potash Alum?

Potash Alum, commonly known as ‘fitkari’, is a chemical compound generally used as the potassium sulfate dodecahydrate. It is a double salt that is primarily used in medicine and the water treatment process. The chemical formula of potash Alum is KAI(SO₄)₂.12H₂O. The other name for the Potash Alum is Potassium Alum or Potassium Aluminium Sulfate.

Potash Alum is a key member of alum that is one of the most renowned coagulants used in the treatment of water, particularly in the low-coloured water. It retains multiple highly intricate species including aluminium polymers in situations that affect the type of product which further relies on the different situations such as dosage, pH, and hydroxide supplement rate and mixing. The versatility also implies that Potash Alum is highly flexible and numerous coagulation mechanisms can be employed.


Aluminum Potassium Sulfate Dodecahydrate

Chemical Formula

KAI(SO₄)₂. 12H₂O

Molar Mass

258.192 g/mol (anhydrous)

474.37 g/mol



1.725 g/cm³

Melting Point

92 to 95 ºC (198 to 203 ºF; 365 TO 368 k)

Boiling Point

200 ºC(392 ºF; 473 K)

What is the Chemical Formula of Potash Alum?

The Chemical Formula of Potash Alum is K₂SO₄.Al₂(SO₄)₃.24H₂O.

Preparation of Potash Alum

Potash Alum is commonly drawn out from alunite minerals. However, potash alum is nowadays produced in industries. One of the most common methods for the preparation of Potash Alum is including potassium sulfate in aluminium sulfate solution which is in concentrated form. If the sulfate includes a large amount of iron apart from potassium sulfate, potassium chloride can be used.

Minerals such as Alum Schist, Bauxite, and Cryolite treated with sulfuric acid are frequently used to procure aluminium sulfate. The liquidized solution containing equal quantities of potassium sulfate and aluminium sulfate is generally formed by crystallization. The crystallization is solid, acidic, and colourless.

A small amount of diluted sulfuric acid is generally used to dissolve aluminum sulfate in the warm water to avoid the hydrolysis of water. During the preparation of potash alum, when a  two-salt solution is permitted to solidify to some extent, a double layer is formed.

The word Alium is given a unique classification of twin salts. Simultaneously, ‘Neutral aluminium’ is produced by mixing sodium carbonate to an aluminium solution.

For the preparation of Potash Alum in the labs, we will require two beakers (250 ml), funnel, funnel kiosk, glass-rod, wire-gauzes, washing bowl, tripod stand, china dish, sulfate of aluminium, potassium, and dilute sulfuric acid.

Procedure For the Preparation of Potash Alum

  1. Take a 250 ml beaker. Wash the beaker and add on 2.5 g potassium sulfate crystals with water. Add about 250 ml of water. Remove the dissolving crystal and let it dry.

  2. Take another 250 ml of sand, wash and use 10 g sulfate crystals of aluminium to the beaker in water. To stop aluminium sulfate hydrolysis, add on around 20 ml of water and 1 ml of distilled sulfuric. Boil for 5 minutes. When milkiness continues, the solution will be filtered. 

  3. In a china-dishware, blend the two dishware solutions and place the china dishware on a wire-gauze on the top of a burner. Condense the solution until it reaches the point of crystallization. Place the dishware over a cold water tumbler.

  4. Remove the potash crystals. Wash and transfer mother’s crystals with ice-cold water in a small portion.

  5. Dry the crystals and disperse them on the pour plate by purifying paper pads.


The Shape of the Crystals


The Colour of the Crystal 


The Action of Blue Litmus Paper

Blue litmus paper turns red

Solubility in Water



  • Do not mess with the solution when it is cooled.

  • Steadily strengthen the solution to obtain stable crystals.

Properties of Potash Alum

The structure of potash alum crystals is octahedral. It is virtually colourless solid and highly soluble in water. Potash alum obtains red colour when heated to a particular degree and then form porous, also known as ‘burnt alum’. As it is prone to very high- temperature, hot molecules of water vaporize and sulfuric acid is released behind a mixture of alumina and potash sulfate.

Potassium aluminium sulfate blends in its crystallization water at 92º C. It is acidic and transforms the colour of the blue litmus.

Usage of Potash Alum

Some of the uses of potash alum are discussed below:

  • Fire Retardant

The uses of potash alum for textiles, wood, and paperless flame defiance is fire-retardant.

  • Tanning

For leather tanning, potash alum is used to draw out moisture from the hide and prevent rotting. Alum is uncovered and can be washed out, in comparison to tannic acid.

  • Used For Dyeing

Potassium alum is used to form permanent milk between natural textile fibres such as wool, and dye, as acid.

  • Pigmentation Of the Lake

Aluminum Hydroxide from potash alum serves as the base for most lake pigments.

  • Gourmet Food

Potassium alum may be an acidic element in baking powder to deliver a second lighten step at high temperature (even though sodium alum is extensively used for this purpose). Bakers in England bake bread with alum during the 1800s.

  • Blocking Chemicals

In ancient times, potassium alum was used for purifying turbid liquids. The drinking water and the industrial water systems, sewage treatment, and post-storm lake methods continue to be primarily used for the treatment of pollutants in precipitation.

Water is used to the domestic wastewater approximately 30 to 40 ppm of alum, but more frequently to the industrial wastewater to cluster negative particles into the snowflake and float them up to the liquid bottom, or more comfortably filter them out of liquid prior further filtration and disinfection of water.

  • Iron and Steel Dissolving

This aluminium solution has the property that steels are dissolved without influencing aluminium or base metals. Alum solution can be used for casting the steel parts of machines.