Alum – Formula, Types, Production, Properties, Uses

Alum is an important inorganic compound which are double sulfates of a monovalent metal (such as potassium, sodium, or ammonium) and a trivalent metal (such as aluminum, chromium, or iron). Alum is widely used in industries as well as medical purposes. It has antiseptic property and is used after shave. It is often called “Fitkari.”

In this article, we learn about alum, its properties, different types of alum, its uses, and many more important facts related to it.

What is Alum?

Alum is an inorganic compound that exists as a hydrated form of double salt. Alum is composed of aluminum, water molecules, and sulphates. Alums are normally found in the form of minerals. XAl(SO4)₂·12H2O is the general chemical formula of alum. Alum can be found in many forms, such as potash alum, soda alum, ammonium alum, and chrome alum.

Alum Formula

Since, alum represents a class of compounds, its general chemical formula is given as follows:

The chemical Formula of Alum is XAl(SO₄)₂.12H₂O

In the above formula, X can be a metal such as potassium (K), sodium (Na), or any other compound such as ammonia (NH₃).

Production of Alum

Most alums are found as minerals. Alunite is one of the most common alum which is occurred as minerals. Potassium, sodium, and ammonium are the other important types of alum that are produced in industries.

• Potassium, sodium, and ammonium alums are produced industrially in the process of combining aluminum sulfate and the sulphate monovalent cation.
• The making process of potassium alum is to dissolve the aluminium sulphate and potassium sulphate in water and heating the solution.
• Due to heating, the solution is evoporated and we will get potassium alum as crystalline.

Properties of Alum

The properties of alum is discussed in the below in a tabular form.

Properties	Details
Chemical Formula	XAl(SO4)2·12H2O
Solubility	Highly soluble in water (especially in hot water)
Taste	Sweet taste
Form	regular octahedral form ( crystalline)
Boiling Point	200℃
Melting Point	92.5℃
Density	1.725 g/cm3

Chemical Properties of Alum

The followings are the chemical properties of alum

• Alums are generally soluble in water, especially sodium alums are easily soluble in water.
• Alums have very sweet taste.
• Alums crystallised into regular octahedra.
• Alums turned blue litmus to red litmus.
• Each metal ion of Alums is surrounded by six water molecules.

Types of Alum

There are a few types of alum available. These are

• Potash Alum
• Soda Alum
• Ammonium Alum
• Chrome Alum
• Selenate Alum

Here we will discuss them briefly in a tabular form. This will help students to understand easily.

Types of Alum	Chemical Formula	Chemical Name	Other names	Molar Mass	Other Properties
Potash Alum	KAl(SO4)2·12H2O	Potassium Aluminium Sulphate	potassium alum, Fitkari	258.192 g/mol	Occur – in white crystalline form Also known as white alum Odor – Metallic Water
Soda Alum	NaAl(SO4)2·12H2O	Sodium Aluminium Sulphate	sodium alum or just SAS	458.28 g/mol	Occur – in white crystalline form It is found in baking soda Odor – Metallic Water
Ammonium Alum	NH3Al(SO4)2·12H2O	Ammonium Sulphate Alum	AAS	132.14 g/mol	Occur – in white crystalline form. Odor – like Metallic Water.
Chrome Alum	KCr(SO4)2·12H2O	Chromium Aluminium Sulphate	Chromium alum is CAS	283.22 g/mol	Occur – in purple crystalline form Odor – Smell like metallic Water
Selenate Alum	Al2O12Se3	Selenium Aluminium Sulphate	Selenium Alum	482.9 g/mol	Strong oxidising agent Occur – Found in white crystalline form Odor – Smell like metallic Water

Uses of Alum

The uses of alum are discussed below:

• It is used in the process of baking and pickling
• In cooking, it is used as an acidulating agent
• Widely used in tanning process of leather.
• It is used as an antiseptic agent.
• In textile company, it is used as drying agent.
• It is used for Water treatment in the process of coagulation and flocculation process
• It is used as an ingredient of toothpaste.
• It acts as an anti-inflammatory agents

Alum Water Treatment

Alum water treatment is generally used to treat polluted waters. To treat polluted water, we use coagulation – flocculation process and in this case, alum is used as a coagulant. Alum treatment is done before the sedimentation and filtration process. The main reason for doing this is to increase the ability of a treatment process to remove unwanted particles.

Coagulation Process

During the coagulation process, the charges on the particles become destabilized. Coagulation of opposite charges of suspended solids is combined to water. To neutralise the negative charges on dispersed non-settable solids, it has to be done.

Al₂(SO4)₃.18H2O + 6HCO^3- → 2Al(OH)₃ + 6CO₂ + 18H₂ + 3SO₄^-2

After doing this, the small particles that are suspended stick together.

Flocculation

To stimulate bonding between different types of particles, we added chemical coagulants to water through a process. This process is known as Flocculation. Through this process, we can get larger aggregates which can separate easily .

Al₂(SO₄)₃.18H₂O + 6HCO^3- → 2Al(OH)₃ + 6CO₂ + 18H₂+ 3SO₄^-2

Facts about Alum

• Alum molecules surrounding by water molecules . But after hearing on high temperature, the water molecules remove and forms amorphous powder.
• Chemical composition of alum is potassium, aluminum, hydrogen, sulphur and oxygen.
• Generally Alums are colourless and odorless.
• Alums have a good flavour and sweet taste.

Conclusion

Alum is an important inorganic compound. It is found in many forms. This article covered all details related to alum including its types, properties etc. This information about alum is enough for a student.

Frequently Asked Questions on Alum

What is alum?

Alum is an inorganic compound which is a hydrated form of double salt. Alum is composed of aluminium, water molecules and sulphates. Alums are normally found as minerals form.

What is the alum used for?

Alum is used widely in various types of industries. The uses of alum are as follows –

1. It is used in the process of baking and pickling
2. In cooking, it is used as an acidulating agent
3. Widely used in tanning process of leather.
4. It is used as an antiseptic agent.
5. In textile company, it is used as drying agent.
6. It is used for Water treatment in the process of coagulation and flocculation process .
7. It is used as an ingredient of toothpaste.
8. It acts as an anti-inflammatory agents

Is alum a fitkari?

Yes, Alum is commonly known as fitkari. Alum and fitkari are the same things. To be more precise fitkari is Potash Alum

Is alum good for skin whitening?

Alum is sometimes used for skin whitening. The use of alum powder can make your skin brighten and lighten. For Skin Tightening and Toning , alum powder is used.

What is the chemical formula of alum?

The chemical Formula of Alum is XAl(SO₄)₂.12H₂O

Is alum water soluble?

Yes, Alum is highly soluble in water.

What are the different types of alum?

There are a few types of alum available. These are – Potash Alum, Soda Alum, Ammonium Alum, Chrome Alum and Selenate Alum

What is the melting point of Alum?

Since there are different types of alum there are different melting points. The melting point of Potash Alum is 92.5 degrees Celsius.