Nickel chloride

Identity and forms

Ideal nickel(II) chloride hexahydrate contains 24.69% nickel by mass, compared with 45.29% for anhydrous NiCl₂. These are formula values. Trace-metals and complexometric assays have different bases, and delivered metal content requires lot evidence. Anhydrous NiCl₂ is CAS 7718-54-9, 129.60 g/mol. Sigma-Aldrich 451193

NiCl₂·6H₂O is CAS 7791-20-0, 237.69 g/mol. Six waters belong to the hydrate formula. Merck 1.06717 identity

Aqueous nickel chloride describes a solution rather than a fixed hydrate composition. Original spectroscopy research distinguishes the solid hexahydrate's NiCl₂(H₂O)₄ coordination unit from the predominantly water-coordinated nickel in the studied solutions. Thus, six formula waters in a crystal do not establish the dissolved coordination structure. Zhang et al., 2015, XAS investigation

Product grades and analytical bases

These declarations describe named products, not universal definitions of nickel chloride grades or current lot results.

Sources: 451193 assay and impurities, 654507 assay and impurities, 1.06717 assay and trace limits.

The two trace-metals products display both assay percentages and separate ppm limits. Their public pages do not explain how those declarations reconcile or specify the denominator of the trace metal analysis. Neither ppm entry is treated here as the arithmetic complement of the assay. 451193, 654507

Thermo Fisher's B22085 SDS lists nickel(II) chloride at ≤100% by weight in section 3. That disclosure is not a minimum assay or a water determination. B22085 U.S. SDS, revision 5, 22 December 2025

Synthesis: a trace-metals basis, complexometric assay, impurity limit, and SDS composition serve different purposes. None alone establishes stoichiometric hydration or the absence of unlisted impurities. No current lot certificate of analysis or independent water measurement was examined.

Formula-equivalent quantities

The following nonprocedural calculations assume ideal pure formula compositions. Inputs are 129.60 g/mol for NiCl₂, 237.69 g/mol for NiCl₂·6H₂O, and 58.6934 g/mol for Ni. CIAAW gives nickel's standard atomic weight as 58.6934(4). Anhydrous formula mass, hydrate formula mass, CIAAW nickel

Derived interpretation: equal masses of ideal anhydrous salt and ideal hexahydrate contain different nickel masses. A concentration expressed as nickel is therefore distinct from the same number expressed as NiCl₂ equivalent or hexahydrate equivalent. These are composition identities, not preparation quantities or operating targets.

A mass percentage has a total-product mass denominator. Molarity has a solution-volume denominator; molality has a solvent-mass denominator. Converting between mass fraction and g/L additionally requires solution density at the applicable temperature. Crystal density and powder bulk density cannot supply that conversion.

Physical-property scope and conflicts

CNESST's anhydrous entry reports density 3.55 g/mL at 20 °C, water solubility 642 g/L at 20 °C, and melting point 1001 °C. Its physical-property section is dated 27 April 1993 and gives no experimental method. The solubility entry does not explicitly distinguish solvent volume from final solution volume. CNESST anhydrous physical properties

Merck 1.06717 lists 2540 g/L solubility without temperature or an explicit volume basis. It also labels density 1.92 g/cm³ and a 140 °C decomposition entry as properties of the anhydrous substance, despite the product's hexahydrate identity. Those labels conflict with the separate anhydrous data above. They remain source-specific entries, not established hydrate constants. Its bulk density is 640 kg/m³ without a packing method. Merck property fields

Thermo Fisher B22085 instead describes water solubility qualitatively as slight. Its SDS supplies no temperature or test method for that entry, no density, and no decomposition temperature. It reports 1001 °C under melting point. The unquantified solubility statement conflicts with CNESST's numerical listing and is not resolved by this research. B22085 SDS, section 9

CNESST separately reports sublimation under vacuum at 973 °C and thermal formation of nickel monoxide. No vacuum pressure or thermal-analysis method is specified. CNESST reactivity section, dated 15 May 1994

Synthesis: melting, water loss, decomposition, and sublimation are different events. These listings do not establish a hydrate-dehydration sequence or a common reversible phase transition. The solubility values cannot be converted into a defensible saturated mass percentage from the stated information.

Bounded aqueous chemistry

Zhang and colleagues studied NiCl₂–water and NiCl₂–MgCl₂–water at ambient conditions using X-ray absorption and UV-visible spectroscopy. The dominant dissolved species was the six-water nickel(II) complex. Minor chloride coordination increased at high salinity. EXAFS fitting constrained total oxygen-plus-chloride coordination to six. Table 2 identifies fixed values, solid standards, and concentrations converted from molarity to molality in cited comparison studies. The finding is therefore an interpreted spectroscopic result with model constraints. Zhang et al., experimental sections, table 2 and footnotes, conclusions

The study used mildly acidified solutions to suppress hydrolysis and reported identical spectra for acidified and non-acidified comparisons. Synthesis: its results do not establish species fractions in arbitrary industrial mixtures, strongly alkaline media, or nonaqueous solvents. Neither the formula nor visible color alone establishes nickel assay, hydration state, or application performance. Zhang et al., sample context and spectroscopy

Hazard and source limits

Thermo Fisher's B22085 U.S. SDS uses OSHA Hazard Communication Standard 2024 classifications. Section 2 includes acute oral and inhalation toxicity Category 3, skin and respiratory sensitization Category 1, carcinogenicity Category 1A, reproductive toxicity Category 1B, and repeated-organ toxicity Category 1. These are dated product-specific classifications, not a global compliance determination. The SDS expressly disclaims being a quality specification. B22085 SDS, sections 2 and 16

Sources were reviewed 30 October 2026 PDT. Manufacturer product pages have no verified revision date. The original research is Zhang et al., PLOS ONE 10(4), e0119805, published 17 April 2015. Coverage excludes current lot composition, complete impurity balances, intermediate hydrate properties, validated solution-density correlations, and application performance. No source establishes customer qualification or production settings.

Related context: Surface-finishing processes.