What is Zinc Chloride?

Zinc chloride is a chemical compound with the formula ZnCl2.

Nine different crystalline forms of zinc chloride are currently known. These hydrates of ZnCl2 are either white in colour or colourless. All of them are highly soluble in water.

Table of Contents

• Zinc Chloride Structure
• Zinc Chloride Preparation
• Properties of Zinc Chloride
• Uses of Zinc Chloride
• Frequently Asked Questions - FAQs

Zinc chloride exhibits hygroscopic qualities, i.e. it attracts and captures the water molecules from the environment. Therefore it is very essential to protect zinc chloride from moisture.

The five known hydrates of zinc chloride have the general formula ZnCl2(H2O)n where the values of n can be 1, 1.5, 2.5, 3, and 4. Solid ZnCl2 exhibits polymorphism and can take on one of the following crystal structures: tetragonal, monoclinic, and orthorhombic.

Zinc Chloride Structure

Zinc chloride is an inorganic binary salt. A molecule of zinc chloride features ionic bonding between the zinc cation (Zn2+) and the chloride anions (Cl-). The structure of a ZnCl2 molecule is illustrated below.

It is important to note that the zinc-chlorine bond in ZnCl2 possesses some covalent characteristics, which accounts for its low melting point and its solubility in ethereal solvents.

Zinc Chloride Preparation

The reaction between metallic zinc and hydrogen chloride gas yields an anhydrous form of zinc chloride. The chemical equation for this reaction is given by:

Zn + 2HCl → ZnCl2 + H2

In order to obtain a hydrated form of the compound, hydrochloric acid can be used to treat zinc instead of hydrogen chloride. Hydrochloric acid reacts with zinc sulphide to form zinc chloride and hydrogen sulphide. The chemical equation for this reaction is given by:

ZnS + 2HCl → ZnCl2 + H2S

Since the only oxidation state exhibited by zinc is +2, the purification of the product is relatively simple.

Properties of Zinc Chloride

Chemical Data

Zinc Chloride ZnCl2 Molar Mass 136.315 grams per mole Density 2.907 grams per cubic centimetre Melting Point 563 K (290oC) Boiling Point 1005 K (732oC)

What are the Uses of Zinc Chloride?

Since it reacts with metal oxides to yield compounds with the general formula MZnOCl2 (Where M is the metal), zinc chloride is used as a flux/cleaning agent for soldering purposes. These fluxes have the ability to dissolve the layer of oxides on the surface of the metal. Some other uses of this compound are listed below.

• In its molten state, this compound acts as a catalyst for some aromatization reactions. For example, hexamethyl benzene can be obtained from methanol with the help of a molten ZnCl2
• Since it acts as a moderately strong Lewis acid, this compound can also serve as a catalyst for the Fischer indole synthesis reaction and some Friedel-Crafts acylation reactions.
• The Lucas reagent is a solution of anhydrous zinc chloride and concentrated hydrochloric acid. This reagent is very useful in the preparation of alkyl chlorides.
• A mixture of zinc oxide and hexachloroethane is used in some smoke grenades. Upon ignition, these compounds react to form a smoke of zinc chloride, which serves as a smokescreen.
• ZnCl2 is also useful in fingerprint detection since it forms an easily detectable complex with Ruhemann’s purple.
• The aqueous solutions of this compound, when diluted, can be used for disinfecting purposes. It is a constituent of several antiseptic mouthwash products.

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