Zinc chloride

Identity and scope

The Merck EMSURE specification lists 98.0–100.5% ZnCl₂ by complexometry and pH 4.6–5.5 for 10% in water. It gives no quantitative free HCl result. Anhydrous ZnCl₂ is CAS 7646-85-7, relative molecular mass 136.3, and is hygroscopic. ILO/WHO, ICSC 1064

Zaclon offers granules and nominal 50%, 62.5%, 65% and 68% solutions. These offerings identify supplied forms and grades. Zaclon, zinc chloride

Documented hydrates

Hennings, Schmidt and Voigt's 2014 single-crystal study reports the following low-temperature crystalline phases. The formulas describe solids, not a complete inventory of ions or complexes in a solution. Original paper, pp. 515–518

The study identifies the 4.5-hydrate below 240 K and distinguishes it from older reports of a 4-hydrate. It also cites earlier work on a hydrate with a water-to-ZnCl₂ ratio of 1.33. This is a bounded set of documented structures, not a claim that every historical hydrate assignment has been independently resolved here. Hennings et al., sections 1 and 4, Table 4

Formula deduction: the trihydrate structural formula contains two zinc atoms and six water molecules, so it represents two ZnCl₂·3H₂O formula units. Its six coordinated waters do not make it ZnCl₂·6H₂O. Formula counting neither measures moisture in a commercial solid nor identifies species in an aqueous product.

Product assay, water and impurity bases

Thermo Fisher's A16281.0C, named “zinc chloride, anhydrous, 98+%,” has a product specification whose freshly retrieved PDF bears Date Of Print: 10/29/2026. Its complete specification panel gives white-to-cream-to-pale-grey crystals, powder or crystalline powder; 97.5–102.5% assay by titration ex chloride; and ≤1.75% water by Karl Fischer titration. The document says specifications may change. These are specification limits, not results for a named lot. The “anhydrous” product name therefore does not mean a zero-water specification. Thermo Fisher, A16281.0C specification

Merck/Supelco 1.08816 EMSURE has these selected product-page entries; they are not an independent reproduction of the standards named in its grade description. Merck/Supelco, 1.08816

“As ZnO” is a reporting basis. The pH percentage has no stated mass/volume basis; other impurity tests are listed separately. Merck/Supelco, analysis note

Interpretive synthesis: chloride-based titration and complexometric assay describe different measured quantities expressed as ZnCl₂ equivalents. An upper assay limit above 100% is not a literal mass fraction above unity. Neither assay alone supplies a complete composition balance. Karl Fischer water, insoluble matter, oxide-chloride reporting and trace-metal limits are separate characteristics; subtracting assay from 100% does not identify the remainder as water.

Neither of these cited specification panels supplies a separate quantitative free-hydrochloric-acid limit. Solution pH is not interchangeable with such a limit, and no free-acid result is deduced here. No named-lot certificate was verified; no current shipment analysis or performance follows from these examples.

Solid properties and numerical differences

The following are source-listed reference properties, separate from the assay specifications above. They are not lot measurements or guaranteed operating limits.

Sources: ICSC physical and chemical information; Merck/Supelco properties.

Interpretive synthesis: solid density concerns the material volume; bulk density includes the spaces between particles and depends on the bulk's condition. The cited bulk range does not state a loose or tapped method. It cannot substitute for a crystal density or a solution density. The melting entries remain different source statements; they have not been averaged or assigned to a particular hydrate or polymorph. ICSC also reports decomposition on heating without supplying a numerical onset, so the tabulated thermal values do not establish a common decomposition-free range. ICSC chemical dangers

Aqueous solutions and solubility

ICSC lists water solubility as 432 g/100 mL at 25 °C, without an equilibrium solid phase or uncertainty. This retains the card's units; no final-solution volume, mass-percent conversion or commercial product concentration is deduced. ICSC 1064

Zaclon's English-US solution SDS, printed 12/03/2019, lists these section 9 values without specific-gravity reference temperatures or boiling-point pressure. Baumé grade labels are not converted to mass percent. Zaclon solution SDS, p. 4

These descriptive SDS values are not assay specifications or batch results. Its unqualified “100%” solubility entry establishes no saturation curve. The older SDS and undated product page have distinct grade contexts. Zaclon SDS, section 9; product page

Hazard and evidence boundaries

The dated Zaclon SDS classifies its solution under GHS-US/CAN as oral acute toxicity category 4, skin corrosion category 1B, single-exposure target-organ toxicity category 3, and acute/chronic aquatic hazard category 1. These are regional, document-specific classifications, not a determination of present worldwide compliance or an approval for an application. Zaclon SDS, sections 1–2

Coverage is limited to chemical identity, selected commercial analytical bases, documented hydrate structures and attributed physical data. It does not establish formulation compatibility, equipment suitability, reaction performance, complete solution speciation or a customer's manufacturing capability. Preparation, process settings and handling procedures are outside this reference.

The Thermo Fisher date above was reproduced in fresh PDF bytes; an older web-reader copy showed a different print date. The original hydrate paper was inspected through its public PMC-hosted PDF copy after direct publisher retrieval was blocked. The undated Merck page was available through the web reader; its date is not treated as a specification revision. These access differences do not turn historical reference data into current lot evidence.

Related reference

Surface-finishing processes