chemistry

Zinc chloride

Zinc chloride is a chemistry topic covered in the lgStudy science library. This page brings together a partial reference excerpt, illustrations, worked examples, real-world applications and a short study plan, so you can understand Zinc chloride rather than just read about it. In short: Zinc chloride is an inorganic chemical compound with the formula ZnCl2·nH2O, with n ranging from 0 to 4.5, forming hydrates. Zinc chloride, anhydrous and its hydrates, are colorless or white crystalline solids, and are highly soluble in water.

Key takeaways

Zinc chloride belongs to chemistry; place it in that map before memorising details.
Learn the definition first, then one example that makes the definition concrete.
Connect Zinc chloride to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of Zinc chloride from memory before moving on to harder problems.

Reference excerpt

Zinc chloride is an inorganic chemical compound with the formula ZnCl2·nH2O, with n ranging from 0 to 4.5, forming hydrates. Zinc chloride, anhydrous and its hydrates, are colorless or white crystalline solids, and are highly soluble in water. Five hydrates of zinc chloride are known, as well as four polymorphs of anhydrous zinc chloride. All forms of zinc chloride are deliquescent. They can usually be produced by the reaction of zinc or its compounds with some form of hydrogen chloride. Anhydrous zinc compound is a Lewis acid, readily forming complexes with a variety of Lewis bases. Zinc chloride finds wide application in textile processing, metallurgical fluxes, chemical synthesis of organic compounds, such as benzaldehyde, and processes to produce other compounds of zinc.

History Zinc chloride has long been known but currently practiced industrial applications all evolved in the latter half of 20th century. An amorphous cement formed from aqueous zinc chloride and zinc oxide was first investigated in 1855 by Stanislas Sorel. Sorel later went on to investigate the related magnesium oxychloride cement, which bears his name. Dilute aqueous zinc chloride was used as a disinfectant under the name "Burnett's Disinfecting Fluid". From 1839 Sir William Burnett promoted its use as a disinfectant as well as a wood preservative. The Royal Navy conducted trials into its use as a disinfectant in the late 1840s, including during the cholera epidemic of 1849; and at the same time experiments were conducted into its preservative properties as applicable to the shipbuilding and railway industries. Burnett had some commercial success with his eponymous fluid. Following his death however, its use was largely superseded by that of carbolic acid and other proprietary products.

Structure and properties Unlike other metal dichlorides, zinc dichloride adopts several crystalline forms (polymorphs). Four polymorph are known: α, β, γ, and δ. Each features Zn2+ centers surrounded in a tetrahedral manner by four chloride ligands.

Here a, b, and c are lattice constants, Z is the number of structure units per unit cell, and ρ is the density calculated from the structure parameters. The orthorhombic form (δ) rapidly changes to another polymorph upon exposure to the atmosphere. A possible explanation is that the OH− ions originating from the absorbed water facilitate the rearrangement. Rapid cooling of molten ZnCl2 gives a glass. Molten ZnCl2 has a high viscosity at its melting point and a comparatively low electrical conductivity, which increases markedly with temperature. As indicated by a Raman scattering study, the viscosity is explained by the presence of polymers. Neutron scattering study indicated the presence of tetrahedral ZnCl4 centers, which requires aggregation of ZnCl2 monomers as well.

Hydrates A variety of hydrated zinc chloride are known: ZnCl2(H2O)n with n = 1, 1.33, 2.5, 3, and 4.5. The 1.33-hydrate, previously thought to be the hemitrihydrate, consists of trans-Zn(H2O)4Cl2 centers with the chloro ligands bridging to tetrachlorozincate ([ZnCl4]2-) groups, present in 1:2 ratio. The hemipentahydrate, structurally formulated [Zn(H2O)5][ZnCl4], consists of Zn(H2O)5Cl octahedra with chloro bridges to tetrachlorozincate tetrahedra. Both the trihydrate and the heminonahydrate possess distinct (unbridged) hexaquozinc cations and tetrachlorozincate anions with the solid structure of the latter ([Zn(H2O)6][ZnCl4]·3H2O) incorporating three additional waters of crystallisation. Each of these hydrates can be produced by controlled evaporation of aqueous zinc chloride solutions under different temperature conditions.

Preparation and purification Historically, zinc chlorides are prepared from the reaction of hydrochloric acid with zinc metal or zinc oxide. Aqueous acids cannot be used to produce anhydrous zinc chloride. According to an early procedure, a suspension of powdered zinc in diethyl ether is treated with hydrogen chloride, followed by drying The overall method remains useful in industry, but without the solvent:

Zn + 2 HCl → ZnCl2 + H2 Aqueous solutions may be readily prepared similarly by treating Zn metal, zinc carbonate, zinc oxide, and zinc sulfide with hydrochloric acid:

ZnS + 2 HCl + 4 H2O → ZnCl2(H2O)4 + H2S Hydrates can be produced by evaporation of an aqueous solution of zinc chloride. The temperature of the evaporation determines the hydrates. For example, evaporation at room temperature produces the 1.33-hydrate. Lower evaporation temperatures produce higher hydrates. Commercial samples of zinc chloride typically contain water and products from hydrolysis as impurities. Laboratory samples may be purified by recrystallization from hot dioxane. Anhydrous samples can be purified by sublimation in a stream of hydrogen chloride gas, followed by heating the sublimate to 400 °C in a stream of dry nitrogen gas. A simple method relies on treating the zinc chloride with thionyl chloride.

Reactions Zinc chloride is an occasional laboratory reagent, often as a Lewis acid.

Chloride complexes A number of salts containing the tetrachlorozincate anion, [ZnCl4]2−, are known. "Caulton's reagent", V2Cl3(thf)6][Zn2Cl6], named for Kenneth G. Caulton, is an example of a salt containing [Zn2Cl6]2− that is used in organic chemistry. The compound Cs3ZnCl5 contains tetrahedral [ZnCl4]2− and Cl− anions, so, the compound is not caesium pentachlorozincate, but caesium tetrachlorozincate chloride. No compounds containing the [ZnCl6]4− ion (hexachlorozincate ion) have been characterized. The compound ZnCl2·0.5HCl·H2O crystallizes from a solution of ZnCl2 in hydrochloric acid. It contains a polymeric anion (Zn2Cl−5)n with balancing monohydrated hydronium ions, H5O+2 ions.

Adducts

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Illustrations

Worked examples

Example 1 — a first encounter with Zinc chloride

Start with the simplest possible case. Write down what Zinc chloride claims or describes in one sentence, then invent the smallest concrete situation in which that sentence is true. In chemistry, the smallest case is usually a single object, a single equation or a single measurement. Check that every symbol or term in your sentence has a meaning in that case.

Example 2 — changing one variable

Take the situation from Example 1 and change exactly one quantity: double it, halve it, or set it to zero. Predict what should happen to Zinc chloride before you calculate. Comparing your prediction with the result is the fastest way to find out whether you understand the idea or only the words.

Example 3 — an exam-style question

Typical questions about Zinc chloride ask you to (a) state it precisely, (b) apply it to given data, and (c) explain a limitation. Practise writing all three answers in under five minutes; the third part is what separates a full-mark answer from an average one.

Applications of Zinc chloride

In research: Zinc chloride appears in chemistry research whenever the underlying quantities have to be modelled precisely. Papers usually cite it as a starting assumption and then explore where it breaks down.
In technology and industry: Engineering practice reuses Zinc chloride in design rules, simulations and safety margins. Knowing the idea lets you read a specification sheet and understand why the numbers look the way they do.
In the classroom: Zinc chloride is common in secondary-school and first-year university syllabi. It links to neighbouring topics Chlorides, Deliquescent materials, Inorganic compounds, so understanding it makes those chapters shorter.
In everyday life: Look for Zinc chloride outside the textbook — in sport, cooking, traffic, electronics or the sky above you. An example you found yourself is remembered far longer than one you were given.

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How to study Zinc chloride in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what Zinc chloride means in your own words.
Compare your version with the excerpt and mark what you missed.
Work through the three examples above with pen and paper.
Explain Zinc chloride out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is Zinc chloride in simple terms?

Why does Zinc chloride matter?

Because it connects several chemistry ideas at once: it gives you a definition you can apply, a quantity you can calculate, and a way to check whether a result is plausible.

How should I study Zinc chloride?

Read the excerpt, restate it from memory, then work through the examples and applications listed on this page. The five-step study plan above takes about twenty minutes.

What does this page cover?

It gives you a compact reference excerpt plus original lgStudy explanations, examples, applications and study material on Zinc chloride.