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.
Table of Content
- What is Alum?
- Production of Alum
- Properties of Alum
- Types of Alum
- Uses of Alum
- Alum Water Treatment
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 |
|
Soda Alum |
NaAl(SO4)2·12H2O |
Sodium Aluminium Sulphate |
sodium alum or just SAS |
458.28 g/mol |
|
Ammonium Alum |
NH3Al(SO4)2·12H2O |
Ammonium Sulphate Alum |
AAS |
132.14 g/mol |
|
Chrome Alum |
KCr(SO4)2·12H2O |
Chromium Aluminium Sulphate |
Chromium alum is CAS |
283.22 g/mol |
|
Selenate Alum |
Al2O12Se3 |
Selenium Aluminium Sulphate |
Selenium Alum |
482.9 g/mol |
|
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 + 6HCO3- → 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 + 6HCO3- → 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.
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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 –
- 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
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.
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