Aluminum Sulfate

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Created by: Team Chemistry -, Last Updated: April 25, 2024

Aluminum Sulfate

Aluminum sulfate, a common inorganic compound in chemistry, plays a crucial role in various everyday applications. Recognized by its chemical formula, Alβ‚‚(SOβ‚„)₃, this compound is primarily used in water purification and textile processing. It appears as a white, crystalline solid and is highly soluble in water. Known for its ability to help particles settle out of solutions. Aluminum sulfate is an effective coagulant, making it essential in producing clean drinking water and in treating wastewater. Its use in gardening to adjust soil pH levels further highlights its versatility, underscoring its importance in both industrial and domestic settings.

What is Aluminum Sulfate?

Aluminum sulfate, often known as alum, is a chemical compound made up of aluminum, sulfur, and oxygen with the formula Alβ‚‚(SOβ‚„)₃. It is typically found as a white powder or crystal and is commonly used in water purification, paper manufacturing, and dyeing processes. In water treatment, it helps to remove impurities by causing them to clump together and settle out of the water, making the water cleaner and clearer. Aluminum sulfate is also used in gardens to lower the pH of the soil, making it more acidic for plants that thrive in such environments. Its versatile uses and effectiveness make it a valuable compound in various industries.

Chemical Names and Formulas

Hill FormulaAlβ‚‚O₁₂S₃
NameAluminum sulfate
IUPAC NameDialuminum trisulfate
Alternate NamesAlum, Aluminium sulfate, Aluminium sulphate, Aluminum sulphate, Dialuminum trisulfate

Structure of Aluminum Sulfate


Aluminum sulfate, represented by the chemical formula Alβ‚‚(SOβ‚„)₃, has a structured composition where two aluminum atoms are bonded with three sulfate groups. Each sulfate group consists of one sulfur atom surrounded by four oxygen atoms. This arrangement forms a complex ionic structure, where the aluminum atoms are positively charged and the sulfate groups are negatively charged. The structure of aluminum sulfate enables it to easily dissolve in water, which is why it’s so effective in water treatment processes for clumping and removing impurities. This simple ionic makeup plays a crucial role in its various applications, from cleaning water to helping adjust soil acidity.

Preparation of Aluminum Sulfate

Aluminum sulfate can be prepared using a simple chemical reaction where aluminum hydroxide reacts with sulfuric acid. The chemical equation for this reaction is:

2Al(OH)₃ + 3Hβ‚‚SOβ‚„ β†’ Alβ‚‚(SOβ‚„)₃ + 6Hβ‚‚O

In this equation, aluminum hydroxide (𝐴𝑙(𝑂𝐻)₃) combines with sulfuric acid (Hβ‚‚SO₄​) to form aluminum sulfate (𝐴𝑙₂(𝑆𝑂₄​)₃) and water (𝐻₂𝑂). This process typically takes place in a controlled industrial setting. Aluminum hydroxide is mixed with sulfuric acid in a reaction vessel, and heat is often applied to speed up the reaction. The resulting mixture is then cooled, and aluminum sulfate crystallizes out of the solution. The crystals are collected and dried, resulting in the aluminum sulfate used in various applications like water treatment and paper manufacturing. This preparation method is not only efficient but also scales well for large production needs.

Physical Properties of Aluminum Sulfate

AppearanceWhite crystalline solid or powder
Solubility in WaterHighly soluble, meaning it dissolves easily in water
Melting PointApproximately 770Β°F (410Β°C)
DensityAbout 2.71 grams per cubic centimeter
pHAcidic (around 3 when in a 1% solution)

Chemical Properties of Borax

Acidic Nature

Aluminum sulfate is acidic. When dissolved in water, it breaks down into aluminum ions and sulfate ions, slightly lowering the pH of the solution. This characteristic is crucial for applications like water treatment and paper manufacturing.


Aluminum sulfate is hygroscopic, meaning it can absorb moisture from the air. This property is particularly useful in industries where moisture control is necessary.

Reaction with Sodium Bicarbonate

When aluminum sulfate is mixed with sodium bicarbonate (baking soda), it leads to a chemical reaction that produces carbon dioxide gas, aluminum hydroxide, and sodium sulfate. The chemical equation for this reaction is:

Alβ‚‚(SOβ‚„)₃ + 6NaHCO₃ β†’ 3COβ‚‚ + 3Hβ‚‚O + 2Al(OH)₃ + 3Naβ‚‚SOβ‚„

This reaction is valuable in fire-extinguishing applications because the carbon dioxide helps to smother flames.

Water Purification

In water treatment, aluminum sulfate helps remove impurities by reacting with them to form larger particles. These larger particles are then easier to filter out, a process known as flocculation, which is essential for producing clean drinking water.

Aluminum Sulfate (Alβ‚‚(SOβ‚„)₃) Chemical Compound Information

Chemical Identifiers

CAS Registry Number10043-01-3
PubChem Compound ID24850
PubChem Substance ID24852105
SMILES Identifier[O-]S(=O)(=O)[O-].[O-]S(=O)(=O)[O-].[O-]S(=O)(=O)[O-].[Al+3].[Al+3]
InChI IdentifierInChI=1/2Al.3H2O4S/c;;31-5(2,3)4/h;;3(H2,1,2,3,4)/q2*+3;;;/p-6/f2Al.3O4S/q2m;3*-2
RTECS NumberBD1700000
MDL NumberMFCD00003423

NFPA Label

NFPA Health Rating1
NFPA Fire Rating0
NFPA Reactivity Rating0

Functions of Aluminum Sulfate

Water Clarification

Aluminum sulfate plays a critical role in water treatment facilities. It clarifies water by binding to impurities and sediment, causing them to form larger particles that settle to the bottom or are easily filtered out. This process makes the water clear and safe for consumption.

pH Regulation

In both industrial applications and gardening, aluminum sulfate is used to adjust pH levels. For paper manufacturing, it stabilizes the pH to ensure quality paper output. In gardening, it acidifies the soil, which is beneficial for acid-loving plants that thrive in lower pH environments.

Dye Fixative

In the textile industry, aluminum sulfate functions as a mordant. It fixes dyes to fabrics, ensuring that colors are vibrant and long-lasting. This chemical reaction not only improves the color quality but also enhances the durability of the dye on the fabric.

Fire Safety

Aluminum sulfate is used in fire extinguisher. It reacts with baking soda to produce carbon dioxide, a gas that helps extinguish flames by suffocating them and reducing the oxygen available to fuel the fire. This makes it an effective component in fire safety measures.

Uses of Aluminum Sulfate


Water Treatment

Water treatment plants widely use aluminum sulfate to clarify water. It removes microscopic impurities by causing them to clump into larger particles that are easily filtered out. Known as coagulation and flocculation, this process makes water safe for drinking.

Paper Manufacturing

In the paper industry, aluminum sulfate is used to control the pH level of pulp during the paper-making process. This helps improve the longevity and quality of the paper. Additionally, it helps the ink adhere better during the printing process.

Garden Product

Gardeners use aluminum sulfate to acidify soil, creating an ideal environment for acid-loving plants like azaleas and rhododendrons. By lowering the soil’s pH, it helps these plants absorb nutrients more effectively.

Dyeing Fabrics

Aluminum sulfate is an important mordant in dyeing textiles. It helps fix dyes onto fabrics by ensuring the dye binds chemically to the fabric, resulting in more vibrant and long-lasting colors.

Fire Extinguisher

Some fire extinguishing formulas include aluminum sulfate because of its reaction with sodium bicarbonate, which produces carbon dioxide. This carbon dioxide helps to smother flames effectively, making it useful in fire extinguishers.

Side Effects of Aluminum Sulfate

  • Skin Irritation: Direct contact with aluminum sulfate can irritate the skin. Prolonged exposure might cause redness, itching, or even a burning sensation.
  • Eye Damage: Exposure to aluminum sulfate can be harmful to the eyes. It can cause severe irritation and redness, and in extreme cases, it might result in permanent eye damage if not washed out immediately.
  • Respiratory Issues: Inhaling aluminum sulfate dust can irritate the respiratory tract. Symptoms can include coughing and shortness of breath, particularly in confined spaces with inadequate ventilation.
  • Environmental Impact: Excessive use of aluminum sulfate, especially in water bodies like lakes and ponds, can lead to environmental imbalance. It can decrease the pH of the water significantly, which may be harmful to aquatic life.
  • Aluminum Exposure: Prolonged exposure to high levels of aluminum from sources like aluminum sulfate may pose health concerns. It can impact the nervous system and potentially link to other health risks, although researchers are still reviewing clear evidence.


Is Aluminum Sulfate Toxic to Humans?

Aluminum sulfate is not highly toxic but can cause irritation to skin, eyes, and respiratory tract if mishandled.

Is Aluminum Sulfate Bad for Soil?

Aluminum sulfate can acidify soil, beneficial for acid-loving plants but potentially harmful to other vegetation.

Is Aluminum Sulfate a Carcinogen?

There is no evidence to suggest that aluminum sulfate is a carcinogen according to major health agencies.

Is Aluminum Sulfate in Baking Powder Bad for You?

Generally, cooking and baking safely incorporate small amounts of aluminum sulfate in baking powder..

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