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Iron III Hydroxide Formula – Structure, Properties, Uses, Sample Questions

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Iron (III) Hydroxide consists of the elements Iron, Oxygen, and Hydrogen. Iron is a metal present in group-8 of the periodic table. It is one of the most common elements found on earth. Its atomic number is 26 and is represented by the symbol Fe. Oxygen is a highly reactive nonmetal present in the chalcogen group, i.e., group-16. Its atomic number is 8 and is represented by the symbol O. Hydrogen is the lightest, colorless, odorless, tasteless, and flammable gas. Its atomic number is 1 and is represented by the symbol H.

Iron (III) Hydroxide Formula

Iron (III) Hydroxide compound is made up of Iron, Oxygen, and Hydrogen elements. Its chemical formula is Fe(OH)3. The color of Iron (III) Hydroxide varies from dark brown to black depending on its crystal structure, hydration, particle size, and shape. It is insoluble in water. The other names of Iron (III) Hydroxide are Ferric Hydroxide and Hydrated Iron Oxide. Anhydrous Ferric Hydroxide occurs in nature very rarely as mineral bernalite, Fe(OH)3.nH2O. And the Iron oxyhydroxides are more common and occur naturally as various minerals represented by the Greek letters α, β, γ, and δ. Some of the Iron oxyhydroxides are Goethite α-FeO(OH), Feroxyhyte, lepidocrocite, Siderogel, etc.

Preparation of Iron (III) Hydroxide

Iron (III) Hydroxide Fe(OH)3 is prepared by adding Sodium Hydroxide (NaOH) to an Iron (III) ion-containing solution. Ferric Hydroxide precipitates as a rust-brown gelatinous solid from the solution. This compound is used to test for the presence of positive metal ions in the solution.

Structure of Iron (III) Hydroxide

Iron (III) Hydroxide structure

Physical Properties of Iron (III) Hydroxide

  • Iron (III) Hydroxide appears in the form of vivid dark orange crystals.
  • Its molecular weight is 106.867 g/mol.
  • The melting point of iron (III) Hydroxide is 135°C.
  • The density of iron (III) Hydroxide is 4.25 g/cm3.
  • Color of Iron(III) Hydroxide can range from yellow to dark-brown to black based on certain conditions like shape, size, structure, etc.

Chemical Properties of Iron (III) Hydroxide

  • Iron (III) Hydroxide is insoluble in water.
  • On heating Iron (III), Hydroxide β-FeOOH decomposes and recrystallizes as Hematite α-Fe2O3.

Uses of Iron (III) Hydroxide

  • Iron (III) Hydroxide is used in aquarium water treatment as a phosphate binder.
  • Yellow Iron oxide is used in a few tattoo inks and cosmetics.
  • It is used as a possible adsorbent for lead removal from aquatic media.
  • Ferric Hydroxide gradually loses water to form a ferric oxide which is used as a pigment, catalyst, and rubber filler.
  • It is used in paper production.

Sample Questions

Question 1: Find the Molecular weight of Iron (III) Hydroxide.


Iron (III) Hydroxide consists of 1 Iron atom, 3 Hydrogen atoms and 3 Oxygen atoms.

Atomic weight of Iron = 55.845

Atomic weight of each oxygen atom = 15.999 

Atomic weight of each Hydrogen atom = 1.00784

Molar mass of Fe(OH)3 = 55.845 + (3 × 15.999) + (3 × 1.00784)

= 106.867

Question 2: What is Amorphous Iron (III) Hydroxide Crystallization?


Hydrolysis of Ferric solutions initially leads to mononuclear and dinuclear species. These species interact to form species with higher nuclearity i.e. polynuclear species. These species age eventually either to the amorphous precipitate or to the crystalline compounds.

Question 3: What are the safety measures to be taken in order to store the Iron (III) Hydroxide?


In normal conditions Iron (III) Hydroxide is stable. But at temperature above 180 °C, it’s color may change gradually. So store/keep it away from furnaces, kilns, boilers and other potential heat sources. Also keep it away from combustible materials.

Question 4: How do you separate solid Iron (III) Hydroxide from solid Sodium Chloride?


Firstly dissolve the mixture containing solid Iron (III) Hydroxide and solid Sodium Chloride in water. As we know that the transition metal (Fe) oxides won’t dissolve in water. So filter out the solution and then boil the filtrate till the water gets completely evaporated. The left ones are pure solid Sodium Chloride crystals. On the other side the dirty brown residue which is derived from the filtration of mixture earlier will be the pure solid Iron (III) Hydroxide.

Question 5: Is Iron (III) Hydroxide hazardous to health?


Yes, Iron (III) Hydroxide is hazardous to health. It may cause eye and respiratory tract irritation. Over exposure to it may lead to short term health issues.

Question 6: Give any use of Iron (III) Hydroxide with an explanation.


Iron (III) Hydroxide is used in paper production form wood. A solution containing Iron (III) Hydroxide and Sodium Sulphide is treated with wood to remove unwanted materials present in the wood to give pure cellulose which is further purified to form basis of water.

Last Updated : 19 Dec, 2023
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