The key difference between ferric and ferrous sulphate is that ferric sulphate has iron in the +3 oxidation state, whereas ferrous sulphate has iron in the +2 oxidation state.
Ferric and ferrous sulphate are sulphates of iron. They are ionic compounds containing cations (iron in different oxidation states) and anions (sulphate anions). The chemical formula of ferric sulphate is Fe2(SO4)3 while the chemical formula of ferrous sulphate is FeSO4.
CONTENTS
1. Overview and Key Difference
2. What is Ferric Sulphate
3. What is Ferrous Sulphate
4. Side by Side Comparison – Ferric vs Ferrous Sulphate in Tabular Form
5. Summary
What is Ferric Sulphate?
Ferric sulphate is a sulphate of iron having the chemical formula Fe2(SO4)3. The iron in this compound is in the +3 oxidation state. The chemical name is Iron(III) sulphate. It is water-soluble and usually appears in yellowish-grey colour crystals. There are anhydrous form as well as some hydrated forms. The molar mass of the anhydrous form is 399.9 g/mol. However, the anhydrous form very rarely occurs in nature. The pentahydrate form (having five water molecules associated with one ferric sulphate molecule) is the most common form.
Figure 01: Appearance of Ferric Sulphate
In the production process, this compound is obtained as a solution rather than a solid. The large scale production involves treating sulfuric acid in the presence of ferrous sulphate and an oxidizing agent (such as chlorine, nitric acid, etc.)
What is Ferrous Sulphate?
Ferrous sulphate is a sulphate of iron having the chemical formula FeSO4. The iron in this compound is in the +2 oxidation state. The chemical name of ferrous sulphate is Iron(II) sulphate. There are both anhydrous forms and hydrated forms. The most common form is the heptahydrate form. It has seven water molecules associated with a ferrous sulphate molecule. This heptahydrate form occurs as blue-green crystals.
Figure 02: Heptahydrate Crystals of Ferrous Sulphate
Ferrous sulphate is commercially prepared by oxidation of pyrite. However, another method that produces this compound in large quantities as a byproduct is the finishing of steel. Here, the steel sheet passes through a pickling bath containing sulfuric acid.
What is the Difference Between Ferric and Ferrous Sulphate?
Ferric and ferrous sulphate are sulphates of iron. The key difference between ferric and ferrous sulphate is that ferric sulphate has iron in the +2 oxidation state, whereas ferrous sulphate has iron in the +3 oxidation state. Ferric sulphate is a sulphate of iron having the chemical formula Fe2(SO4)3 while ferrous sulphate is a sulphate of iron having the chemical formula FeSO4. The anhydrous forms of these compounds are rare; therefore, we can find the most common hydrated form of ferric sulphate as the pentahydrated form; the most common form of ferrous sulphate is the heptahydrate form.
Furthermore, the most common hydrated form of ferric sulphate appears in yellowish-grey crystals while ferrous sulphate appears in blue-green crystal form. Therefore, this is an easily distinguishable difference between ferric and ferrous sulphate. When considering the production process, we can produce ferric sulphate via treating sulfuric acid in the presence of ferrous sulphate and an oxidizing agent (such as chlorine, nitric acid, etc.). Meanwhile, we can produce ferrous sulphate via oxidation of pyrite. However, another method that produces this compound in large quantities as a byproduct is the finishing of steel.
Summary – Ferric vs Ferrous Sulphate
Ferric and ferrous sulphate are sulphates of iron. The key difference between ferric and ferrous sulphate is that ferric sulphate has iron in the +2 oxidation state, whereas ferrous sulphate has iron in the +3 oxidation state.
Reference:
1.“Ferric Sulfate.” National Center for Biotechnology Information. PubChem Compound Database, U.S. National Library of Medicine, Available here.
2. “Iron(II) Sulfate.” Wikipedia, Wikimedia Foundation, 18 Sept. 2019, Available here.
3. “Iron(III) Sulfate.” Wikipedia, Wikimedia Foundation, 23 Sept. 2019, Available here.
4. “Compounds.” Encyclopædia Britannica, Encyclopædia Britannica, Inc., 13 June 2019, Available here.
Image Courtesy:
1. “Síran železitý” By Ondřej Mangl – Own work (Public Domain) via Commons Wikimedia
2. “Iron(II)-sulfate-heptahydrate-sample” By Benjah-bmm27 – Own work (Public Domain) via Commons Wikimedia