What Is Aluminium Sulfate Definition Formula Reactions and Applications
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.
Aluminium Sulfate Al2(SO4)3 Uses
Let us now learn about the common uses of Aluminium Sulfate.
Aluminium Sulfate is used in the purification of water.
It is used to prepare baking soda.
It is used for dyeing clothes.
It is used for gardening purposes and helps to balance the soil pH.
Aluminium Sulfate is used in making paper.
It is also used for making different prints on cloth.
It is used in concrete as a waterproofing agent and an accelerator.
It is used in making the firefighting foam.
It is also used in the treatment of sewage in water treatment plants.
Aluminium Sulfate is used as a fireproofing agent.
FAQs on Aluminium Sulfate Structure Properties Preparation and Uses
1. What is aluminium sulfate?
Aluminium sulfate is an inorganic ionic compound with the formula Al2(SO4)3 that consists of aluminium ions and sulfate ions. It is commonly found as a white crystalline solid and is highly soluble in water.
- It contains Al3+ and SO42- ions.
- It forms acidic solutions due to hydrolysis of Al3+.
- It is widely used in water treatment, paper manufacturing, and dyeing.
2. What is the chemical formula for aluminium sulfate?
The chemical formula for aluminium sulfate is Al2(SO4)3.
- Each formula unit contains 2 aluminium ions (Al3+).
- It also contains 3 sulfate ions (SO42-).
- The charges balance because 2 × (+3) = +6 and 3 × (−2) = −6.
3. How is aluminium sulfate prepared?
Aluminium sulfate is prepared by reacting aluminium oxide or aluminium hydroxide with sulfuric acid.
- From aluminium oxide:
Al2O3(s) + 3H2SO4(aq) → Al2(SO4)3(aq) + 3H2O(l) - From aluminium hydroxide:
2Al(OH)3(s) + 3H2SO4(aq) → Al2(SO4)3(aq) + 6H2O(l)
4. Why is aluminium sulfate used in water treatment?
Aluminium sulfate is used in water treatment because it acts as a coagulant that removes suspended impurities by forming flocs.
- In water, Al3+ undergoes hydrolysis to form gelatinous Al(OH)3.
- This precipitate traps dirt, bacteria, and colloidal particles.
- The flocs settle down, allowing cleaner water to be separated.
5. Is aluminium sulfate acidic or basic?
Aluminium sulfate forms an acidic solution in water due to hydrolysis of the aluminium ion.
- The Al3+ ion reacts with water:
Al3+(aq) + 3H2O(l) ⇌ Al(OH)3(s) + 3H+(aq) - The release of H+ ions lowers the pH.
- Therefore, its aqueous solution is acidic.
6. What happens when aluminium sulfate reacts with sodium hydroxide?
When aluminium sulfate reacts with sodium hydroxide, it forms a precipitate of aluminium hydroxide and sodium sulfate.
- The balanced equation is:
Al2(SO4)3(aq) + 6NaOH(aq) → 2Al(OH)3(s) + 3Na2SO4(aq) - Al(OH)3 appears as a white gelatinous precipitate.
- This is a double displacement and precipitation reaction.
7. What is the molar mass of aluminium sulfate?
The molar mass of aluminium sulfate, Al2(SO4)3, is approximately 342.15 g·mol−1.
- Al: 2 × 26.98 = 53.96 g·mol−1
- S: 3 × 32.06 = 96.18 g·mol−1
- O: 12 × 16.00 = 192.00 g·mol−1
- Total = 342.14 ≈ 342.15 g·mol−1
8. What type of compound is aluminium sulfate?
Aluminium sulfate is an ionic compound composed of metal cations and polyatomic anions.
- It contains Al3+ (a metal ion).
- It contains SO42- (a polyatomic anion).
- The ions are held together by strong electrostatic forces.
9. What are the common uses of aluminium sulfate?
Aluminium sulfate is mainly used in water purification, paper manufacturing, and dyeing textiles.
- In water treatment, it acts as a coagulant.
- In the paper industry, it helps in sizing and improving paper quality.
- In dyeing, it works as a mordant to fix dyes to fabrics.
- It is also used in soil treatment to lower pH.
10. What is the difference between aluminium sulfate and alum?
Aluminium sulfate (Al2(SO4)3) is a simple salt, while alum is a double sulfate salt containing aluminium and another metal ion.
- Example of common alum (potash alum): KAl(SO4)2·12H2O.
- Aluminium sulfate contains only Al3+ and SO42-.
- Alum contains Al3+, another cation such as K+, and water of crystallization.
