Zinc Iodide Formula: Preparation, Properties & Uses

Zinc iodide is an inorganic compound with the chemical formula ZnI₂. Zinc iodide exists in two forms anhydrous and dihydrate form. The dihydrate form of zinc iodide is written as ZnI₂.2H₂O. 

• The molecular mass of zinc iodide is 319.19 g/mol.
• Zinc iodide is hygroscopic in nature.
• Zinc iodide is a strong electrolyte.

Key Terms: Zinc Iodide, Zinc, Iodide, Inorganic compound, Anhydrous form, Dihydrate form

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Zinc Iodide Formula

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The molecular formula for zinc iodide is ZnI₂. It is found as a white granular powder. When exposed to air and sunlight it turns brown in colour due to the liberation of iodine. It is an odorless compound with a sharp saline taste.

• Zinc iodide readily absorbs moisture from the atmosphere. 
• The IUPAC name for zinc iodide is Diiodizinc.
• Zinc iodide is also known as zinc diiodide.

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Preparation of Zinc Iodide

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Zinc Iodide is prepared in laboratories by the reaction of zinc with iodine in water or refluxing ether. The chemical reaction is given as,

Zn + I₂ → ZnI₂

• It can also be prepared by the reaction of zinc with iodine in an aqueous solution. 
• Zinc iodide is also prepared by adding zinc powder to a solution of iodine in ethanol and an exothermic reaction takes place. A solution of zinc iodide is obtained from which zinc iodide can be obtained by evaporating the solvent.

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Structure of Zinc Iodide

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In the crystal form of zinc iodide, zinc centres are tetrahedrally coordinated. The group of four of the zinc tetrahedra shares three vertices to form “super-tetrahedra” of composition with the formula, [Zn₄I₁₀]. They are linked via vertices and form a 3-D structure.

The gaseous state, zinc iodide possesses a linear shape in accordance with the VSEPR Theory. In an aqueous state, it forms a tetrahedral structure in the case of ZnI₂.(H₂O₂).

Structure of Zinc Iodide

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Properties of Zinc Iodide

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The properties of zinc iodide are-

• It is a hygroscopic compound.
• The melting point of zinc iodide is 446℃.
• The boiling point of zinc iodide is 1150℃.
• The density of zinc iodide is 4.74g/cm³.
• It is soluble in alcohol and alkalis.

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Uses of Zinc Iodide

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The uses of zinc iodide are-

• Zinc iodide is commonly employed as a catalyst for the conversion of methanol to triptane.
• It is used in industrial radiography as an X-Ray opaque penetrant to improve damage and intact composite contrast of the X-Ray.
• A combination of zinc iodide with osmium tetroxide is utilized as a stain in electron microscopy.
• It is used in aqueous zinc-halogen rechargeable cells as an electrolyte.

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Things to Remember

• The chemical formula for zinc iodide is ZnI₂. 
• Zinc iodide is a Lewis acid.
• Zinc iodide is highly soluble in water
• DiIododzinc is the IUPAC name for zinc iodide.
• Zinc iodide is known to be a strong electrolyte.
• Zinc Iodide is used in industrial radiography.
• Zinc iodide is held together by ionic bonds.

Learn More: 

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Previous Year Questions

1. Zinc can be coated on iron to produce galvanized iron but the reverse is not possible. It is because- (NEET- 2016)
2. A 5 A current is passed through a solution of zinc sulphate for 40 min. The amount of zinc deposited at the cathode is- (NEET-1996)
3. In the electrolytic refining of Zinc - (KCET-2010)
4. The cell Zn|Zn2+(1M)| |Cu2+(1M)| Cu (E…- (AIEEE-2007)
5. Extraction of zinc from zinc blende is achieved by- (JEE Advanced- 2007)
6. When the same amount of zinc is treated separately with excess of sulphuric acid and excess of sodium hydroxide, the ratio of volumes of hydrogen evolved is- (JEE Advanced-1979)
7. When mercuric iodide is added to the aqueous solution of potassium iodide- (JEE Advanced 1987)