Aluminium Sulfate - Al₂(SO₄)₃

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Properties of Aluminium Sulfate Al₂(SO₄)₃

The chemical formula of Aluminium Sulfate is Al2(SO4)3. It is a chemical compound typically used as a coagulating agent for purification of drinking water, paper manufacturing, and wastewater treatment plants. It is also known as filter alum or dialuminium trisulfate. It is a white crystalline solid in its anhydrous form. However, in its liquid form, it is colourless. Both these forms are non-combustible and non-toxic.

Aluminium Sulfate is water-soluble but insoluble in ethanol. It does not have any odour and has a mildly astringent and sweet taste. When it decomposes it emits highly toxic fumes of Sulphur oxides. Also, the Aluminium Sulfate solution is corrosive to Aluminium. This is produced in the laboratory when Aluminium Hydroxide is added to Sulphuric Acid. Here, we will learn about what is Aluminium Sulfate Al2(SO4)3, the properties of Aluminium Sulfate Al2(SO4)3, its structure and uses.

Aluminium Sulfate Structure Al2(SO4)3 Structure

Now that you have learned what is Aluminium Sulfate, let us take a look at its structure and how it looks. Given below is its structure.

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Aluminium Sulfate Formula

Let us now learn the formula of Aluminium Sulfate and how is this formula derived chemically.

Aluminium Sulfate is known to be an ionic compound, which means that it is a combination of both positive and negative ions. An atom or molecule turns into an ion when it loses or gains electrons. Molecules can be either monatomic, which means that they contain one atom, or polyatomic, which means that they contain more than one atom. Most ionic compounds consist of a one metal atom that is a positive ion, and a radical or negative ion that is a negative ion. 

If you consider Aluminium Sulfate, the positive ion in it is Aluminium ion, Al3+. The radical is the sulfate ion, (SO4)2- that has a negative charge. 

Since all ionic compounds are electrically neutral, there is a ratio of molecular weight by which the aluminum and sulfate ions react, so their electrical charges are cancelled out. You can determine this ratio by the criss-cross method of deriving a chemical formula. Let us see how this method works.

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Here, the sign on the sulfate ion is reversed. Then the charges are put as subscripts on the opposite ion. 

Properties of Aluminium Sulfate Al2(SO4)3

Let us now learn about the properties of Aluminium Sulfate Al2(SO4)3. Take a look at the below table.




2.672 g/cm3

Molecular Weight or Molar Mass

342.15 g/mol

Boiling Point

214° F

Melting Point

770 °C

Aluminium Sulfate Al2(SO4)3 Uses

Let us now learn about the common uses of Aluminium Sulfate.

  1. Aluminium Sulfate is used in the purification of water.

  2. It is used to prepare baking soda.

  3. It is used for dyeing clothes.

  4. It is used for gardening purposes and helps to balance the soil pH.

  5. Aluminium Sulfate is used in making paper.

  6. It is also used for making different prints on cloth.

  7. It is used in concrete as a waterproofing agent and an accelerator.

  8. It is used in making the firefighting foam.

  9. It is also used in the treatment of sewage in water treatment plants.

  10. Aluminium Sulfate is used as a fireproofing agent.

FAQ (Frequently Asked Questions)

1. How is Aluminium Sulfate made?

Ans: Aluminium Sulfate is formed in the laboratory when the right amount of Sulphuric Acid is added to freshly precipitated Aluminium Hydroxide. Then the resulting solution is evaporated and allowed to crystallize. It is accessible as pure, lustrous crystals, powder, or granules. The reaction is given as follows.

3H2SO4 + 2 Al(OH)3 → Al2(SO4)3 + 6H2O

Aluminium Sulfate can also be prepared when Aluminum metal is heated in a Sulfuric acid solution. The reaction is given below.

2 Al + 3 H2SO4 → Al2(S04)3 + 3 H2

2. Is Aluminium Sulfate dangerous?

Ans: Aluminium Sulfate is not carcinogenic. However, it is known to be a skin and eye irritant, so in case you are working with it, you should be careful and wear gloves and take eye protection. If you, by any chance, tend to ingest Aluminum Sulfate in some way, it is mildly hazardous since it tends to form Sulfuric Acid which is very corrosive in nature. 

When you mix Aluminum Sulfate with water, it forms highly toxic Sulfuric Acid which tends to burn eyes and skin. Any kind of contact with the skin causes itching, red rashes, and a burning feeling whereas inhaling it irritates the lungs and throat. When it is inhaled, it immediately causes shortness of breath and coughing. Also, consuming Aluminum Sulfate has a highly negative effect on your intestinal lining and stomach. In most cases, the person starts to vomit, feel nauseous and gets diarrhea.