Chromium III Sulfate Formula – Structure, Properties, Uses, Sample Questions

Chromium (Cr), a chemical element of Group 6 (VIb) of the Periodic Table, is used in alloys to increase strength and corrosion resistance-gray metal. Chromium is used in the quenching of steel, the production of stainless steel (named because it does not rust), and the production of various alloys. Chrome plating can be used to give the steel a highly polished finish.

Sulfate is a sulfur oxoanion obtained by deprotonating both OH groups of sulfuric acid. It plays a role as a human metabolite, a metabolite of Saccharomyces cerevisiae, and a cofactor. It is a sulfur oxo anion, a sulfur oxide, an inorganic anion, and a divalent inorganic anion.

Chromium (III) sulfate Chromium (sulfate III) is an inorganic compound with a ratio of chromium to sulfate of 2: 3. The formula for chromium (III) sulfate is Cr₂(SO₄)₃. It is also a blue-gray solid that dissolves in water. When heated, it changes from blue to green. Let’s learn the formula of chromium(III) sulfate here.

Chromium sulfate (III) is usually an inorganic compound of formula Cr₂(SO₄)₃.x(H₂O). x is between 0 and 18. In addition, the undefined but commercially important “basic chromium sulfate” is well known. These salts usually have a purple or green solid that dissolves when placed in water. It is often used for tanning leather materials.

Structure of Chromium (II) sulfate

Production of Chromium (III) Sulfate

• Chromium(III) sulfate is formed as a by-product of the  Jones Oxidation process. In this process, a solution of sodium dichromate or potassium dichromate is dissolved in sulfuric acid to oxidize the alcohol.  

3C₂H₅OH  +  2 K₂Cr₂O₇  +  8H₂SO₄    ⇢  2Cr(SO₄)₃  +  3CH₃COOH + 2H₂SO₄  + 11H₂O

• Chromium (III)sulfate can also be obtained by treating chromium hydroxide (III) with dilute sulfuric acid.

Cr(OH)₂ + H₂SO₄  ⇢  CrSO₄ + 2H₂O

• Chromium (III) sulfate is formed by a double displacement reaction between chromium chloride and sulphuric acid.

2CrCl₃ + 3H₂SO₄     ⇢  Cr₂(SO₄)₃ + 6HCl

Physical properties of Chromium (III) Sulfate

• Molar mass- 392.16 g/mol (anhydrous)
• It is a Blue-gray solid
• Chemical Formula is Cr₂(SO₄)₃
• Melting Point – 90 °C
• Boiling Point – greater than 700 °C
• Density -3.1 g/cm³ (anhydrous)

Chemical properties of Chromium (III) Sulfate

•  When chromium(III) sulfate reacts with cesium phosphate it gives Chromium phosphate and cesium sulfate, which is a double displacement reaction.

Cr₂(SO₄)₃  +  2Cs₃PO₄    ⇢  2CrPO₄  + 3Cs₂SO₄

• When Potassium sulfate reacts with chromium(III) sulfate, potassium chromium alum is formed.

K₂SO₄  +  Cr₂(SO₄)₃  +  24H₂O  ⇢  2KCr(SO₄)₂ . 12H₂O ⇣

Uses

• Used as an electrolyte to obtain chrome metal.
• Used to chrome plating other metals for decorative and protective purposes.
• Used as a mordant for tanned leather.
• Gives green color to varnishes, paints, ceramic glazes, and inks.

Sample Questions

Question 1: What is the oxidation of Cr in Cr₂(SO₄)₃?

Answer: 

Now consider that the oxidation number of Cr is x.

 Since Cr₂(SO₄)₃ is a molecule, its oxidation number is 0.

This is the normal oxidation number of (SO₄) = -2.

Therefore, mathematically,

2 x + 3 (-2) = 0

2x = +6

x = +3

Cr₂(SO₄)₃ has an oxidation number of Cr of +3.

Question 2: What kind of compound is chromium (III) sulfate? Is it ionic or molecular? 

Answer:

Chromium(III) Sulfate Cr₂(SO₄)₃ is an ionic compound, Cr is a metal with a Cr⁺³ cation, and sulfate is a SO₄^-2 anion. Sulfur and oxygen atoms are in parentheses, indicating covalent bonds between them. Cr has no square brackets, indicating that it is not a polyatomic ion.

Question 3: Why does Chromium Sulfate III turn green when heated? 

Answer: 

Chromium (III) complexes generally exhibit slow ligand exchange. When the aqueous Answer of this compound is heated, the color turns green as a result of the slow dissociation of the water ligand and the coordination of the sulfate ions.

Question 4: Calculate the number of sulfate ions in 39.2 g of chromium sulfate. 

Answer:

Gram molecular mass of Cr2(SO4)3 = 392.6 g

No. of moles in 30 g of Cr₂(SO₄)₃ = 30/392.6 = 0.07 mol

1 mol of Cr₂(SO₄)₃ contains = 3 x 6.023 x 1023 sulfate ions

So, No. of Sulfate ions in 0.07 mol of Cr₂(SO₄)₃ will be= 0.07 x 3 x 6.023 x 1023

= 1.2648 x 10²³.

Question 5: How to determine the formula for chromium (III) sulfate? 

Answer:

To determine the formula for chromium (III) sulfate, we use a criss-cross method that exchanges the charges carried by the cations and anions present in the ionic compound. Chromium III has a valence of 3 and sulfate has a valence of 2. Two chromium ions and three sulfate ions are required to balance the six valence bonds. Therefore, the charge carried by the chromium cation Cr⁺³ is written as an index of the sulfate anion SO₄^-2, and the charge carried by the sulfate anion SO₄^-2 is written as an index of the chromium cation Cr + 3. The polyatomic ion SO4-2 is enclosed in parentheses. Therefore, to obtain the formula for chromium (III) sulfate, exchange the charges of ions Cr⁺³ and SO₄^-2 to obtain Cr₂ and (SO₄)₃. If you write these two together, you will get Cr₂(SO₄)₃.

Question 6: What is the use of chromium sulfate?   

Answer:

The uses of chromium sulfate are as follows:

1. Widely used in the leather industry in the tanning process.
2.  Used for dyeing textile dyes, especially khaki fabrics.  
3. Also used in green paints, ceramic glazes, and inks.  
4. Used in chrome plating to decorate and protect the metal. 

Question 7: Does Chromium III Sulfate dissolve in water?  

Answer:

Chromium sulfate (III) usually refers to an inorganic compound of formula Cr₂(SO₄)₃. x(H₂O), where the range of x is 0-18. In addition, “basic chromium sulfate”, which is not clearly defined but is commercially important, is known. These salts are usually purple or green solids that are soluble in water.