Difference Between Iron Ii Chloride And Iron Iii Chloride

Iron chlorides, specifically Iron II Chloride and Iron III Chloride, are key substances used across various sectors, including water treatment and manufacturing. Both compounds involve iron and chlorine, but differ significantly in their chemical properties and applications. The distinction between these two forms of iron chloride is not only fundamental to chemistry but also critical for their effective use in industry.

Iron II Chloride, also known as ferrous chloride, is an iron salt where iron is in a +2 oxidation state. Conversely, Iron III Chloride, known as ferric chloride, involves iron in a +3 oxidation state. These oxidation states result in different chemical behaviors and applications, which makes understanding these differences crucial for professionals in chemistry and related fields.

Both iron chlorides are essential in numerous applications but serve different purposes based on their chemical properties. Their unique characteristics influence everything from their role in water purification systems to their use in organic synthesis, making a clear understanding of each type vital for their appropriate application in industrial processes.

Basic Chemistry

Definition of Iron II Chloride

Iron II Chloride, commonly referred to as ferrous chloride, is a chemical compound with the formula FeCl₂. It consists of iron in the +2 oxidation state paired with two chloride ions. Iron II Chloride is typically found in its anhydrous form as a white or pale green solid, but it is more commonly encountered as a tetrahydrate (FeCl₂·4H₂O), which takes on a more familiar green crystalline form. This compound is highly soluble in water, which facilitates its use in various applications, particularly in water treatment and metallurgy.

Definition of Iron III Chloride

Iron III Chloride, known as ferric chloride, bears the chemical formula FeCl₃. This compound involves iron in the +3 oxidation state. Unlike its ferrous counterpart, ferric chloride is typically seen in an anhydrous form as dark brown crystals and is highly deliquescent, making it capable of absorbing moisture from the environment. Iron III Chloride is also available in various hydrated forms, including the common hexahydrate (FeCl₃·6H₂O) which appears as orange to brown crystals. Due to its strong oxidizing properties, it is extensively used as a coagulant in wastewater treatment and in the electronics industry for etching copper.

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Physical Properties

Color and Form

The physical appearance of iron chlorides can give immediate insights into their chemical nature. Iron II Chloride in its anhydrous state is pale green to white, but when hydrated, it transforms into green crystals, which is a clue to its lower oxidation state and relatively milder reactivity. In contrast, Iron III Chloride anhydrous forms are dark brown, and its hexahydrate variant has an orange to brown coloration, indicative of its higher oxidation state and greater reactivity.

Solubility Differences

The solubility of iron chlorides in water is a critical characteristic that influences their industrial application. Iron II Chloride is moderately soluble in water, which allows it to be used effectively in solutions for various chemical applications. On the other hand, Iron III Chloride exhibits high solubility in water and its ability to absorb moisture easily (deliquescence) makes it particularly useful in scenarios where a strong and rapid reaction is beneficial, such as in water treatment processes.

Chemical Behavior

Reactivity with Oxygen

The reactivity of iron chlorides with oxygen is significantly influenced by their oxidation states. Iron II Chloride tends to oxidize to Iron III Chloride in the presence of oxygen, especially when exposed to moisture. This transition highlights its relatively unstable nature under atmospheric conditions. Conversely, Iron III Chloride is already in a higher oxidation state and does not further oxidize; instead, it can act as an oxidizing agent, facilitating reactions that require the removal of electrons from other substances.

Hydration States

Hydration states play a crucial role in the physical and chemical properties of iron chlorides. Iron II Chloride typically exists as a tetrahydrate in its most stable form, indicating its propensity to bond with water molecules. This hydrated form is crucial for its application in scenarios that require a controlled release of iron ions. Iron III Chloride, on the other hand, is more commonly found in its hexahydrate form, which not only affects its solubility but also its efficacy as a coagulating and etching agent. The higher hydration state of ferric chloride reflects its stronger interaction with water molecules, making it more effective in applications requiring aggressive chemical reactions.

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Production Methods

Synthesis of Iron II Chloride

The production of Iron II Chloride primarily involves the reaction of iron with hydrochloric acid. This method is favored for its simplicity and effectiveness in producing high-purity ferrous chloride. The synthesis can be outlined in a few steps:

  • Iron Metal Reaction: Iron filings or scrap iron are added to hydrochloric acid. The acid reacts with the iron to form Iron II Chloride and hydrogen gas.
  • Filtration: The resulting mixture is filtered to remove any unreacted iron and impurities.
  • Evaporation: The filtered solution is then evaporated under reduced pressure to obtain crystallized Iron II Chloride.
  • Drying: Finally, the crystals are dried in a desiccator to remove excess moisture and to achieve the desired anhydrous or hydrated form.

This method allows for control over the hydration state of the product by adjusting the evaporation and drying stages, making it versatile for different industrial needs.

Synthesis of Iron III Chloride

Iron III Chloride is typically produced through two main methods: direct chlorination of iron and the oxidation of Iron II Chloride. Each method suits different scale operations and purity requirements.

  • Direct Chlorination: Iron is reacted directly with chlorine gas at high temperatures. The reaction produces anhydrous Iron III Chloride as a brownish solid.
  • Oxidation Method:
    • Start with Iron II Chloride, either as a solid or in solution.
    • Oxidize the Iron II Chloride using chlorine gas or by aerating it in a hydrochloric acid solution.
    • The oxidation results in the formation of Iron III Chloride, which can be further processed to achieve the desired purity and hydration state.

Both methods are effective, but the choice of method often depends on the required volume and specific industrial application.

Industrial Applications

Uses in Water Treatment

Iron III Chloride is extensively used in water treatment facilities due to its efficacy as a flocculant and coagulant. In water treatment, Iron III Chloride helps in:

  • Removal of Suspended Solids: It causes fine particles and suspended solids to coagulate into larger flakes, which are easier to filter out from water.
  • Phosphate Removal: It is effective in removing phosphate from wastewater, which helps in preventing algal blooms in bodies of water.
  • Heavy Metal Precipitation: It aids in the precipitation of heavy metals from industrial wastewater, enhancing the safety and cleanliness of water released into the environment.

Roles in Organic Synthesis

Both Iron II and Iron III Chlorides play significant roles in organic chemistry, particularly in the synthesis of organic compounds:

  • Catalysis: Iron III Chloride is a powerful Lewis acid and serves as a catalyst in various organic reactions, including the Friedel-Crafts acylation, which is pivotal in synthesizing aromatic ketones.
  • Reducing Agent: Iron II Chloride acts as a reducing agent in organic synthesis, particularly in reactions requiring mild reduction conditions.
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Environmental Impact

Safety Concerns

Handling iron chlorides requires caution due to their corrosive nature and potential health risks:

  • Corrosive Effects: Both iron chlorides are highly corrosive to metals and can cause severe skin burns and eye damage upon contact.
  • Respiratory Issues: Inhalation of dust or fumes from iron chlorides can cause respiratory irritation and should be managed with appropriate safety gear and ventilation.

Disposal Guidelines

Proper disposal of iron chlorides is crucial to minimize their environmental impact. Disposal should follow these guidelines:

  • Neutralization: Before disposal, neutralize the acidic solutions of iron chlorides to prevent damage to sewage systems and reduce the risk to aquatic life.
  • Regulatory Compliance: Always comply with local environmental regulations regarding the disposal of chemical waste to ensure that it does not harm the environment or public health.

Frequently Asked Questions

What is Iron II Chloride?

Iron II Chloride, or ferrous chloride, is a chemical compound consisting of iron in a +2 oxidation state. It is commonly used in water treatment processes and in the synthesis of various organic compounds.

What is Iron III Chloride?

Iron III Chloride, or ferric chloride, is a compound where iron exists in a +3 oxidation state. It is widely utilized for its coagulating properties in wastewater treatment and as a catalyst in organic reactions.

How do Iron II Chloride and Iron III Chloride differ?

The primary difference between Iron II Chloride and Iron III Chloride lies in their oxidation states, which influences their chemical reactivity and applications. Iron II Chloride is less oxidizing compared to Iron III Chloride, making them suitable for different industrial applications.

Why are different oxidation states important in Iron Chlorides?

The oxidation state of iron in iron chlorides affects their reactivity, solubility, and the types of reactions they can participate in. This is crucial for their use in specific industrial processes, such as water purification and the production of specialty chemicals.


The differences between Iron II Chloride and Iron III Chloride play a pivotal role in their applications across various industries. Their unique properties dictate their suitability for specific tasks, ranging from treating wastewater to facilitating chemical syntheses. A thorough understanding of these compounds not only enhances their effective utilization but also underscores the importance of detailed chemical knowledge in industrial applications.

In conclusion, while both Iron II and Iron III Chlorides are essential in their respective rights, their effective deployment is highly dependent on the knowledge of their distinct characteristics. This knowledge ensures their optimal use in industry, maximizing efficiency and sustainability in processes that rely on these versatile compounds.

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