Main Difference – Ferric vs Non Ferric Alum
Alum is any chemical compound with the general empirical formula AB(SO4)2·12H2O where A is a monovalent cation and B is a trivalent metal ion. The most common monovalent cations are potassium and ammonium. The most common trivalent metal ions are aluminum and chromium (III). There are different types of alums. Ferric alum and non-ferric alum are such two types. Ferric alum is Ammonium Iron (III) sulfate. Non ferric alum is a purer form of ammonium sulfate which does not have iron in its chemical composition. The main difference between ferric alum and non-ferric alum is that ferric alum is manufactured from bauxite whereas non-ferric alum is manufactured from aluminum trihydrate.
Key Areas Covered
1. What is Ferric Alum
– Definition, Chemical Properties, Uses
2. What is Non Ferric Alum
– Definition, Manufacturing
3. What is the Difference Between Ferric and Non Ferric Alum
– Comparison of Key Differences
Key Terms: Alum, Ammonium Sulfate, Dehydration, Ferric, Iron, Isometric, Monovalent, Octahedron, Trivalent
What is Ferric Alum
Ferric alum is Ammonium Iron (III) sulfate. The formula for this compound is NH4Fe(SO4)2·12H2O. It is known as a double sulfate of ammonium and iron. Here, iron is in the oxidation state of iron (III). This is considered as an alum because it has the general empirical formula for an alum with a monovalent cation and a trivalent metal ion. Although it is called an alum, there is no aluminum in its composition.
This is a solid substance having isometric (cubic) crystal system. The crystal structure is an octahedron. This ferric alum has a light violet color in big specimens. But smaller crystals look colorless. Ferric alum is not stable. When exposed to dry air, these crystals quickly dehydrate. This dehydration causes the loss of color and transparency of the ferric alum crystals.
Figure 1: Ferric Alum
Therefore, ferric alum is kept in tightly closed containers or placed in a suitable oil or other hydrophobic liquid. Bauxite is used to manufacture ferric alum. Here, bauxite is produced from the reaction between bauxite and sulfuric acid under controlled conditions.
Ferric alum is used as a water treatment chemical because it can act as a coagulating agent. Therefore some suspended solids can be removed using ferric alum. Ferric alum has about 0.5% of insoluble matter. The amount of iron present is around 0.7% as soluble iron.
What is Non Ferric Alum
Non-ferric alum is the purer form of ammonium sulfate. It has no ferric ions in its chemical composition. This substance is manufactured using aluminum trihydrate as the raw material. The raw material is reacted with sulfuric acid under suitable conditions to produce non-ferric alum.
Non-ferric alum has 0.02-0.03% of insoluble matter by mass. Although it has no ferric ions, there can be iron in the form of Fe (around 0.004%). Non-ferric alum lacks the violet color in ferric alum. Instead, non-ferric alum is colorless. It is opaque.
Figure 2: Non Ferric Alum
Non-ferric alum is soluble in water. Therefore it can be used as a chemical reagent for water purification. But there can be primary hazards for the environment. It is used as a chemical reagent in chemical analysis. Non-ferric alum is also used in paper manufacturing as a loading material.
Difference Between Ferric and Non Ferric Alum
Definition
Ferric Alum: Ferric alum is Ammonium Iron (III) sulfate.
Non Ferric Alum: Non ferric alum is the purer form of ammonium sulfate.
Raw Material
Ferric Alum: The raw material used for manufacturing of ferric alum is bauxite.
Non Ferric Alum: The raw material used for manufacturing of non-ferric alum is aluminum trihydrate.
Presence of Iron
Ferric Alum: The amount of iron present in ferric alum is around 0.7% as soluble iron.
Non Ferric Alum: Non-ferric alum has about 0.004% of iron as Fe.
Insoluble Matter
Ferric Alum: Ferric alum has about 0.5% of insoluble matter.
Non Ferric Alum: Non-ferric alum has about 0.02-0.03% of insoluble matter.
Conclusion
Alum is a water soluble substance having a general formula of AB(SO4)2·12H2O. It has a monovalent cation and a trivalent metal ion as essential components in its chemical composition. There are two types of alum as ferric alum and non-ferric alum. The main difference between ferric alum and non-ferric alum is that ferric alum is manufactured from bauxite whereas non-ferric alum is manufactured from aluminum trihydrate.
References:
1. Helmenstine, Anne Marie. “What Is Alum? Facts and Safety.” ThoughtCo, Nov. 20, 2017, Available here.
2. Non ferric alum purer form of aluminum sulphate chemical properties. Available here.
3. Ferric Alum. Dishmin, Available here.
Image Courtesy:
1. “Ammonium iron(III) sulfate dodecahydrate” By Bob Collowân – Own work (CC BY-SA 4.0) via Commons Wikimedia
2. “Aluminium sulfate” (Public Domain) via Commons Wikimedia
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