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

Aluminium Sulphate is a chemical compound that is soluble in water. It is predominantly used as a coagulating agent in the purification of drinking water and wastewater treatment plants. It is likewise utilized in the paper manufacturing process. The anhydrous structure of aluminium sulphate is obtained from the volcanic environment and in coal mining. It is obtained in the form of the rare mineral millosevichite.

Aluminium Sulphate is also known as alum or papermaker's alum in particular industries. Aluminium Sulphate solution appears to be a colourless liquid while its anhydrous structure appears as a crystalline solid. The above forms of aluminium sulphate mentioned are non-toxic and non-explosive respectively.

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

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Aluminium Sulphate formula:

The chemical formula for aluminium sulphate 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 Sulphate is 342.15 g/cm³.

This is the aluminum sulphate formula.

Preparation:-

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

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

It can also be prepared by heating aluminium in the 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 and 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 sulphate 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 formed. It is then evaporated until iron (II) sulfate crystalline 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 sulphate is an exothermic reaction. The clear solution is extracted after being allowed to stand for a specific extent of time. In this way, aluminium sulphate 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 sulphuric acid solution. In this way, aluminium sulphate is manufactured using cryolite ore.

Aluminium Sulphate - Al₂(SO₄)₃ is salt composed of aluminium, oxygen and sulfur. It consists of positive and negative ions called cations and anions respectively. Thus, the above statement confirms that aluminium sulphate is an ionic compound. The formation of ions occurs when an atom or a molecule gains or loses an electron or electrons from the shell. Most of the time, ionic compounds consist of a positive ion or a cation being the metal atom and a negative ion or anion being a radical or a negative ion.

The cation and the anion in the aluminium sulphate molecule are (Al3⁺) and (SO^3-₄) respectively.

The chemical formula of aluminium sulphate 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^3-₄)

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.

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N factor 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 charge on ionic species (n factor) i.e ratio of molecular weight of salt to the n factor.

Now, 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^3-₄.

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

Aluminium Sulfate uses:

• Aluminium Sulphate 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 Sulphate 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.

• Aluminium Sulphate 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 neutralize the charges when used in the pulp itself.

• Aluminium Sulphate helps in regulating algal growth in water bodies. Aluminium Sulphate 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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NCERT Chemistry Notes:

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