What is Ferric Chloride?
Ferric chloride is an inorganic compound with formula FeCl3 which has numerous industrial, pharmaceutical and laboratorial uses. In this article we will discuss ferric chloride structure with its physical and chemical properties, ferric chloride test for phenols and applications in various fields.
Ferric chloride is named as iron chloride. It is a chemical compound with a chemical formula consisting of FeCl3.
It has a relatively low melting point as compared to its boiling point, which is around 315 degrees Celsius. When dissolved in water, ferric chloride goes through the hydrolysis process and gives off heat in an otherwise exothermic reaction.
It is produced in industries by the reaction of dry chlorine with scrap iron at 500 to about 700 degrees Celsius temperature .
Ferric chloride is a common compound of iron and chlorine in which iron possesses +3 oxidation state. It’s IUPAC name is Iron(III) chloride or Iron trichloride. Apart from ferric chloride it has several common names such as molysite and flores martis. It possesses various colors such as in its anhydrous form it appears black-green or purple while in its hydrous form it appears yellow solid.
It is also used variably in the production of various printed circuit boards. It is used in indigo blue dyestuff production as an oxidant. In the laboratory, ferric chloride is commonly used as Lewis acid for conducting catalyzing reactions such as friedel crafts reaction of aromatics and chlorination of aromatic compounds. In its raw form, ferric chloride is a solid hygroscopic crystal. Its color is mostly dependent on the viewing angle. In reflected light, the crystals appear to be very dark green in color. In transmitted light, they appear to be purple red. Ferric chloride is very readily soluble in liquids with donor properties, such as alcohols, ketones, ethers, nitriles, amines, and liquid sulfur dioxide, but it is sparingly soluble in non polar solvents like benzene and hexane.
Ferric chloride is harmful, highly corrosive and acidic in nature. The anhydrous material is a powerful dehydrating agent in return. Although poisoning in humans is rare, ingestion of ferric chloride can result in a case of serious morbidity and contributes to the mortality rate.
The most common use of the ferric chloride is in its solution form. When it is dissolved, it forms a light brown aqueous solution with a faintly hydrochloric acid odor. It is highly corrosive into most metals and most probably corrosive to tissues. It is noncombustible and primarily used in various sewage treatment and water purification processes. Industrial uses include the different manufacturing ways of pigments, plating agents and surface treating agents, process regulators, and solids separation agents. Ferris chloride is produced industrially in a process which is called direct chlorination. It is a process in which a reaction takes place of dry chlorine with scrap iron at 500-700 degrees Centigrade.
It is a covalent compound although iron is a metal and chlorine is a non-metal. In ferric chloride, iron gets partial positive charge and chlorine atoms get partial negative charge as chlorine is more electronegative than iron so it pulls a shared electron pair towards itself.
Properties of Ferric Chloride
Physical Properties
Its chemical formula is FeCl3.
Its molar mass is 162.2 g/mol (anhydrous).
It looks purple - red or green – black in its anhydrous form while yellow solid as hexahydrate.
Its aqueous solution looks brown in color.
It has a faint HCl odor.
Its melting point is 307.6℃ in its anhydrous form.
It shows 316℃ boiling point in its anhydrous form.
It is highly soluble in methanol and diethyl ether.
Chemical Properties
Ferric chloride shows following chemical reactions –
Reaction with iron (III) oxide
FeCl3 + Fe2O3 🡪 3FeOCl
Reaction with copper (I) chloride
FeCl3 + CuCl 🡪 FeCl2 + CuCl2
Reaction with chlorobenzene to give ferrous chloride
2FeCl3 + C6H5Cl 🡪 2FeCl2 + C6H4Cl2 + HCl
Reaction with organometallic compound LiCH3
2FeCl3 + LiCH3 🡪 FeCl2 + LiFeCl4 + .CH3
Preparation of Ferric Chloride
Anhydrous ferric chloride can be prepared by reaction of iron and chlorine. The reaction is given below –
2Fe(s) + 3Cl2(g) 🡪 2FeCl3(s)
Preparation of Aqueous Ferric Chloride
Aqueous ferric chloride can be prepared by following three methods –
By dissolving iron ore in HCl
Fe3O4(s) + 8HCl(aq) 🡪 FeCl2(aq) + 2FeCl3(aq) + 4H2O(l)
By oxidation of ferrous chloride with chlorine
2FeCl2(aq) + Cl2(g) 🡪 2FeCl3(aq)
By oxidation of ferrous chloride with oxygen
4FeCl2(aq) + O2 + 4HCl 🡪 4FeCl3(aq) + 2H2O(l)
Ferric Chloride Test
Ferric chloride test is performed to know the presence or absence of phenol in a sample. It is a traditional colorimetric test for phenols. It is performed by following steps –
Take 1% ferric chloride solution that has been neutralized with sodium hydroxide until a slight precipitate of FeO(OH) is formed. It is filtered before use.
The organic substance or sample is dissolved in water, methanol or ethanol in a test tube.
Now the above taken neutralized ferric chloride solution is added in the test containing the solution of the sample.
If transient or permanent purple, green or blue coloration occurs then it indicates the presence of phenol or enol group in the sample.
Applications of Ferric Chloride
Ferric chloride is used in various fields. Few of its uses are given below –
It is used in sewage treatment.
It is used in production of printed circuit boards.
It is used as a catalyst in many reactions.
It is frequently used in laboratories.
It is used for colorimetric tests for phenols.
It can also be used to test gamma-hydroxybutyric acid and gamma -butyrolactone.
It is used as a drying reagent in many reactions.
It is used by bladesmiths and artisans in pattern welding.
It is used to strip aluminum coating from mirrors.
It is used to etch intricate medical devices.
The primary usage of ferric chloride is to remove impurities in water and it is used for wastewater treatment. Ferric chloride is also one of the few existing water treatment chemicals which can permit odors.
Ferric chloride (i.e, FeCl3) is the most common iron salts which is used to achieve coagulation. Its reactions in the coagulation process are quite similar to those of alum, but its relative solubility and pH range differ significantly than those of alum metal. Both alum and ferric chloride can be used for generating various inorganic polymeric coagulants.
At high concentrations, chloride can harm the fish and plant life kingdom. But there is no easier and a more affordable way to remove chloride in the wastewater. It would require a reverse osmosis, the same process which is used to produce water for laboratory use, technically difficult as well as costly.
Alum is a nontoxic liquid that is commonly used in water treatment plants to purify drinking water. It is used in lakes to reduce the amount of phosphorus in the water. Ferrous Chloride is a pale, greenish color, salt like crystal or powder. It is used in various textile dyeing, metallurgy, the pharmaceutical industry, and sewage treatment processes.
The ferric chloride test is used to determine the presence of phenols in a given sample or compound, or natural phenols in a plant extract. Enols, hydroxamic acids, oximes and sulfinic acids give definitive positive results as well.
Chemicals are added to the water to bring the non settling particles together into larger, heavier masses of solids called floc. Aluminum sulfate is the most common coagulant which is used for water purification.
After flocculation, the water flows into the existing sedimentation tanks. Chloride increases the electrical conductivity of water molecules and it thus increases its corrosivity. In metal pipes, chloride reacts with various metal ions to form various soluble salts. It increases levels of metals in drinking water. In lead pipes, a protective oxide layer is built up, but chloride always enhances the galvanic corrosion. Residential water softeners are often the cause of salty discharge into municipal wastewater systems.
The salt used for the brine can be the reason for elevated chloride levels. Ferrous Chloride is a corrosive substance and its contact can irritate and burn the eyes and skin. Breathing Ferrous Chloride can irritate the nose and the throat systems. Prolonged contact may also cause brown discoloration of the eyes and can harm it.
Anhydrous iron (III) chloride can be prepared by reacting metallic iron with dichlorine. Ferric Chloride Test is conducted to determine the presence or absence of phenol in a given sample.
FAQs on Ferric Chloride
1. What is ferric chloride and what is its chemical formula?
Ferric chloride is an inorganic compound of iron and chlorine. Its chemical formula is FeCl₃, and its IUPAC name is Iron(III) chloride, which indicates that the iron atom is in its +3 oxidation state. It is a common compound used widely in industrial processes and as a laboratory reagent.
2. What are the key physical and chemical properties of ferric chloride?
Ferric chloride exhibits several distinct properties that are important for its applications:
- Appearance: Anhydrous FeCl₃ crystals appear as dark-green or purple-red depending on the viewing angle. The common hydrated form, hexahydrate (FeCl₃·6H₂O), is a yellowish-brown solid.
- State: It is a solid at room temperature with a relatively low melting point of 307.6 °C for the anhydrous form.
- Solubility: It is highly soluble in water and other donor solvents like alcohols and ethers.
- Nature: It is hygroscopic (absorbs moisture from the air) and highly corrosive. Its aqueous solution is acidic due to hydrolysis.
- Chemical Property: It acts as a strong Lewis acid, readily accepting electron pairs in chemical reactions.
3. What are the most common industrial and laboratory uses of ferric chloride?
Ferric chloride has several important applications across various fields:
- Water Treatment: Its primary use is as a coagulant and flocculant in sewage treatment and drinking water purification to remove impurities.
- Electronics: It is used as an etchant in the manufacturing of printed circuit boards (PCBs) to remove unwanted copper.
- Chemical Synthesis: It serves as a catalyst in organic reactions, most notably the Friedel-Crafts alkylation and acylation of aromatic compounds.
- Laboratory Reagent: It is used in the ferric chloride test to detect the presence of phenols, which produces a characteristic colour change.
4. Why is an aqueous solution of ferric chloride acidic?
An aqueous solution of ferric chloride is acidic due to a process called salt hydrolysis. When FeCl₃ dissolves in water, the Fe³⁺ ion gets hydrated. The high positive charge and small size of the Fe³⁺ ion give it a strong polarising power. It attracts the electrons of the surrounding water molecules so strongly that it weakens their O-H bonds, causing the release of hydrogen ions (H⁺) into the solution. This increase in H⁺ concentration makes the solution acidic, lowering its pH.
5. Why is anhydrous ferric chloride, and not the hydrated form, used as a catalyst in Friedel-Crafts reactions?
Anhydrous ferric chloride is used because its function as a catalyst depends on it being a strong Lewis acid, meaning it can accept an electron pair. Water is a Lewis base and would react with the ferric chloride. If the hydrated form (FeCl₃·6H₂O) were used, the water molecules already bonded to the iron ion would interfere with its ability to accept electrons from the reactants in the Friedel-Crafts reaction, thus rendering the catalyst ineffective.
6. How does ferric chloride work as a coagulant in wastewater treatment?
In water treatment, ferric chloride acts as a coagulant by neutralising the charge of colloidal particles. It hydrolyses in water to form iron(III) hydroxide, Fe(OH)₃, a gelatinous precipitate. This precipitate has a large, positively charged surface area that attracts and neutralises the negatively charged colloidal impurities (like silt and organic matter). This process, called coagulation, causes the small particles to clump together into larger, heavier masses called 'floc', which can then be easily removed by sedimentation and filtration.
7. Ferric chloride is a compound of a metal and a non-metal. Why does it exhibit significant covalent character?
Despite being formed from a metal (Fe) and a non-metal (Cl), ferric chloride has significant covalent character due to the principles described by Fajan's rules. The iron(III) ion (Fe³⁺) is small and has a very high positive charge (+3). This gives it a strong polarising power, allowing it to distort the electron cloud of the larger chloride ion (Cl⁻). This distortion leads to a significant degree of electron sharing between the iron and chlorine atoms, which is the definition of a covalent bond.
8. How is the ferric chloride test performed to detect the presence of phenols?
The ferric chloride test is a simple colorimetric method. The procedure is as follows:
- A neutral solution of 1% ferric chloride is prepared.
- The organic sample to be tested is dissolved in a suitable solvent like water or ethanol.
- A few drops of the neutral FeCl₃ solution are added to the sample solution.
- The formation of an intense, transient or permanent colour, typically violet, green, or blue, indicates the presence of a phenolic (-OH) group. This colour is due to the formation of a coloured iron-phenol coordination complex.
