Aluminium Sulfate - Formula, Preparation, N-factor, Uses, FAQs

A white crystalline solid, which is highly soluble in water and chemically known as Al₂(SO₄)₃ is Aluminium Sulfate, also known as alum. Aluminium Sulfate is widely used in commercial and industrial processes. You must be aware that water, before reaching our houses, is cleaned and purified by municipal water treatment facilities, and these treatment facilities widely use Aluminium sulfate as a coagulating agent that binds with dirt and other impurities, leading to the formation of large flocs which can be filtered easily. Apart from water treatment plants, this compound is used in the paper and textile dyeing industries. This compound is acidic, and due to this property, it is also used as a pH regulator in some processes. This compound is inexpensive and can be easily accessed.

This Story also Contains

1. Formula and Structure of Aluminium Sulfate :
2. Preparation:-
3. N factor of Al2(SO4)3 and equivalent weight-
4. Aluminium Sulfate uses:

In this article, we cover the concept of Aluminium Sulfate, which falls under the chapter P-block in Group 13, which is important for boards and JEE Mains Exam and NEET entrance exam.

Aluminium Sulfate is odourless and has a sweet taste. It is a water-soluble chemical compound, but is insoluble in ethanol. Aluminium Sulfate emits lethal fumes of sulfur oxide after undergoing the decomposition process.

Formula and Structure of Aluminium Sulfate :

The chemical formula for aluminium sulfate can be represented as - Al₂(SO₄)₃

Dialuminium Trisulfate or Filter alum are some of the other terms used to address aluminium sulphate.

The molar mass of Aluminium Sulfate is 342.15 g/cm³.

This is the aluminium sulfate formula.

Preparation:-

Aluminium Sulfate can be prepared in the laboratory by the following method-

• Aluminium Sulfate is prepared by the addition of aluminium hydroxide-Al(OH)₃ to sulphuric acid- H₂SO₄.

It can also be prepared by heating aluminium in a solution of sulfuric acid.

• Similarly,Al₂(SO₄)₃ is also manufactured from alum schists, clays or bauxite and cryolite respectively.

Alum schists comprise iron pyrite, aluminium silicate, and several bituminous elements. They undergo the roasting process, where sulphuric acid is formed and made to act on the clay to form aluminium sulphate. A comparable requirement of conditions is produced during the weathering. process; being another process followed for the production of aluminium sulphate.

The mass retrieved is now systematically removed with water and aluminium sulfate solution is prepared of required specific gravity. This solution is made to stand for some duration of time to separate. Calcium and basic iron(III) sulfate are formed. It is then evaporated until iron (II) sulfate crystallises out on chilling. It is then drawn off and evaporated until it gains the required specific gravity and is allowed to stand for some time followed by decantation.

• The material is calcinated lightly and then blended with sulphuric acid and water and heated progressively to boiling. If concentrated acid is utilized then no external warmth or heat is required as the formation of aluminium sulfate is an exothermic reaction. The clear solution is extracted after being allowed to stand for a specific extent of time. In this way, aluminium sulfate is extracted from clay or bauxite.

• Calcium carbonate is blended with cryolite ore and heated resulting in the formation of sodium aluminate. It is then again heated and precipitated by using sodium bicarbonate or by passing a current of carbon dioxide via the solution. The precipitate is then dissolved in a sulphuric acid solution. In this way, aluminium sulfate is manufactured using cryolite ore.

The cation and the anion in the aluminium sulfate molecule are (Al³⁺) and (SO^2-₄), respectively.

The chemical formula of aluminium sulfate can be derived as described below-

The valency of aluminium is 3, and hence it forms a tri cation: (Al³⁺)

The valency of sulfate ion is 2 and so it forms a

dianion: (SO^2-₄)

The ions combine in a way to form an electrically neutral salt.

By cross-multiplying their valencies we get –

Al₂(SO₄)₃

The combination of ions takes place in such a way that they form an electrically neutral salt.

N factor of Al₂(SO₄)₃ and equivalent weight-

N factor is the capability of accepting or releasing electrons. This ability is reflected by a change in the oxidation state of the species.

Hence, the n factor for salts can be simply defined as the multiplication of charges of ions present in the salt.

Equivalent weight is defined as the ratio of molecular mass of the charged ions and charges on ionic species (n factor) i.e. ratio of molecular weight of salt to the n factor.

How to find n factor of Al₂(SO₄)₃:

Let us find the n factor of Al₂(SO₄)₃

Al₂(SO₄)₃ compound consists of aluminium and sulfate ions having charges +3 and -2 respectively.

These ions are symbolised as – Al³⁺ and SO^2-₄.

By multiplying the charges present in the ions, we get-

3 × 2 = 6

And so, the n factor for Al₂(SO₄)₃ is 6.

Equivalent weight can be given as = M/n factor

= M/6

Related Topics:

• Sulphuric Acid
• Digonal Relationship Between Beryllium And Aluminium
• Alkaline Earth Metals

Aluminium Sulfate uses:

• Aluminum Sulfate functions as a mordant in the dyeing industry. It assists the dye in printing on paper or a piece of fabric.

• Aluminium Sulphate's major use in the industrial sector is as a coagulant in water treatment plants. Aluminium Sulfate when mixed with water results in the formation of several forms having varied ionizing levels capable of attracting contaminants present in water and precipitating them out.

• Aluminum Sulfate finds its application in paper manufacturing industries as well. It is used to eliminate unwanted foreign particles along with water. It also helps in adhering to materials and neutralizing the charges when used in the pulp itself.

• Aluminium Sulfate helps regulate algal growth in water bodies. Aluminium Sulfate being an acidic compound is often used by gardeners to adjust the soil pH.

• It is also used as an accelerator and waterproofing agent in the concrete business.

• One can find its application as a firefighting foam and fireproofing agent as well.

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