Preparation of Potash Alum: Steps, Observations and Uses

Potash alum is often known as potassium alum. Aluminium sulphate, also known as dodecahydrate, is a chemical compound. It is primarily used in water purification, dyeing, tanning leather, and baking powder. It crystallises into regular octahedrons with flattened corners. Potash alum has the chemical formula - K₂(SO₄)·Al₂(SO₄)₃·24H₂O. Potash alum is water-soluble and slightly acidic as it causes litmus paper to turn red. We will look into the preparation of Potash Alum in detail in this article.

Keyterms: Potash alum, Alum, Aluminium sulphate, Dodecahydrate, Chemical compound, Baking powder, Octahedrons, Electricity, Corrosion, Resistance, Conductor, Transmission

---

Alum & Its General Formula

[Click Here for Sample Questions]

Aluminium is widely used in the manufacture of aeroplanes, automotive, lawn furniture, and aluminium cans due to its low density, high tensile strength, and corrosion resistance. It is used for electricity transmission because it is a good conductor of electricity. Aluminium is also used in the manufacture of utensils. 

Varied Uses of Aluminium

Recycling aluminium cans and other aluminium products contributes significantly to the conservation of our natural resources. A significant proportion of recycled aluminium is softened and recast into other aluminium alloy products, or it is used to create various aluminium compounds, the most common of which are alums.

Alums are double sulphates with a general formula,

X₂(SO₄)·M₂(SO₄)₃·24H₂O 

Some notable alums are listed below, along with their names:

1. Potash Alum -  K₂(SO₄)·Al₂(SO₄)₃·24H₂O
2. Soda Alum - Na₂(SO₄)·Al₂(SO₄)₃·24H₂O
3. Chrome Alum - K₂(SO₄)·Cr₂(SO₄)₃·24H₂O
4. Ferric Alum - (NH)₂(SO₄)·Fe₂(SO₄)₃·24H₂O

Out of these, Potash Alum is a very useful compound that finds application in many of the chemical reactions.

Also Read:

---

What is Potash Alum?

[Click Here for Sample Questions]

Potash alum is often known as potassium alum. Aluminium sulphate, also known as dodecahydrate, is a chemical compound. It is primarily used in water purification, dyeing, tanning leather, and baking powder. It crystallises into regular octahedrons with flattened corners. Potash alum has the chemical formula - K₂(SO₄)·Al₂(SO₄)₃·24H₂O

Potash Alum

---

Properties of Potash Alum

[Click Here for Sample Questions]

• Potash alum is water-soluble and causes litmus paper to turn red. 
• It is produced by crystallising alum from a concentrated solution with the presence of different concentrations of potassium sulphate and aluminium sulphate.
• It has no colour.
• It is a crystalline solid with a sour flavour.
• It is commonly referred to as 'fitkari.'

---

Preparation of Potash Alum

[Click Here for Sample Questions]

The preparation reaction of Potash Alum is given below.

K₂(SO₄)(aq) + Al₂(SO₄)₃(aq) → K₂(SO₄)·Al₂(SO₄)₃·24H₂O(s) (Potash Alum)

Requirements 

The following are the requirements for the preparation of Potash Alum

Sample: 

• Ammonium sulphate 
• Aluminium Sulphate
• Ice 

Apparatus:

• Two 250ml beaker 
• China Dish 
• Funnel
• Funnel Stand 
• Glass Rod 
• Wash Bottle

Procedure 

Step 1: 2.5g of potassium sulphate crystals are transferred to a clean 250ml beaker, and 20ml of water is added and stirred until the crystals are dissolved.

Step 2: Then, in another beaker, 10g of aluminium sulphate crystals are added to which 20ml of water and 1ml of dilute H₂SO₄ are added to avoid the hydrolysis of aluminium sulphate.

Step 3: After about 5 minutes of heating, if the milkiness persists, filter the solution. 

Preparation of Potash Alum

Step 4: Further, the two solutions are then combined in a china dish that has been placed on a wire gauze that has been placed over a burner.

Step 5: The solution is stirred with a glass rod and concentrated until the crystallisation point is attained, and the beaker is placed in cold water.

Step 6: The crystals of potash alum are separated almost immediately, and the mother liquor must be decanted, and the crystals must be washed with a small amount of ice-cold water.

Potash Alum Crystals

The powders have been discovered to be white small crystals with an octahedron shape.

Preparation of Potash Alum - Observations

• The colour of the Crystal is Colourless
• The shape of the Crystal is octahedral.
• The Crystals are Soluble in water
• During the experiment, the blue litmus becomes red.

---

Applications of Alum

[Click Here for Sample Questions]

1. Potash alum is used in papermaking, fire extinguishers, food, and water purification.
2. Chrome alum is used in tanning leather and waterproofing fabrics, while soda alum is used in baking powders.

Purification of water using Potash Alum

Aside from these primary applications, alum is also used for:

• Astringent - A chemical or preparation that continues to draw together or restricts body tissues, thereby preventing the flow of blood or other secretions. Conventional hairdressers have also used alum to treat shaving cuts.

Shaving Astringent

• A mordant - It is a substance used in dyeing to keep certain dyes from bleeding through the fabric. The mordant or a mordant-produced colloid adheres to the fibre, attracting and fixing the colloidal mordant dye. A lake is formed when an insoluble, coloured precipitate forms. Alum is a basic mordant that is used to fix acid dyes.
• To remove phosphate from natural and wastewaters - The aluminium ions of alum integrate with the orthophosphate around pH 6 to form the precipitated solid aluminium hydroxy phosphate.
• Fabrics for fireproofing - It is used in fireproofing certain fabric types. The following chemical reaction is the principle behind the process of fireproofing.

Al(H₂O)₆⁺³→ Al(OH)₃ + 3H₂O + 3H⁺

The H⁺ ions produced are used to interact with sodium bicarbonate to produce carbon dioxide. This property is used in baking powder as well as CO₂ fire extinguishers.

---

Things to Remember

• Potash alum crystals are octahedral in shape.
• Take precautions while preparing potash alum - To obtain good crystals, slowly cool the solution. While the solution is cooling, do not disturb it.
• Potash Alum is a nearly colourless solid that is easily soluble in water.
• When heated to a certain temperature, it turns red and forms a porous, cold weight known as 'burnt alum.' 
• When exposed to extremely high temperatures, hot water molecules evaporate and sulfuric acid is released, leaving a mixture of alumina and potash sulphate behind.

Also Read: