# Nickel acetate

Nickel(II) acetate identities, hydration and metal-content bases, supplier assays, physical-property limits, and dated hazard evidence.

Reviewed: 2026-10-30

Tags: chemicals, nickel, acetates

## Identity and scope

Ideal **nickel(II) acetate tetrahydrate contains 23.587% nickel by mass**, compared with **33.201%** for anhydrous nickel(II) acetate. The hydrate contains 71.042% anhydrous-salt equivalent. These formula values describe pure forms. Delivered material requires an assay or lot evidence. The Nickel REACH Consortia groups both under nickel acetate. [Nickel Consortia substance page](https://www.nickelconsortia.eu/nickel-acetate.html) [substance identity profile](https://www.nickelconsortia.eu/assets/files/consortia/SIPs/2022/Nickel%20Acetate%20-%20updated%20in%202022.pdf)

| Form | Formula basis | CAS number | Molar mass | Evidence |
| --- | --- | --- | --- | --- |
| Anhydrous nickel(II) acetate | Ni(CH₃COO)₂, also C₄H₆NiO₄ | 373-02-4 | 176.78 g/mol | [Sigma-Aldrich 940631](https://www.sigmaaldrich.com/US/en/product/aldrich/940631) |
| Nickel(II) acetate tetrahydrate | Ni(CH₃COO)₂·4H₂O | 6018-89-9 | 248.84 g/mol | [Sigma-Aldrich 244066](https://www.sigmaaldrich.com/US/en/product/aldrich/244066) |

The Roman numeral II denotes nickel in oxidation state +2. The formula contains two singly charged acetate anions per nickel. This is a stoichiometric description, not a statement that an aqueous solution contains only one molecular species. The anhydrous product's structural identifier explicitly represents Ni²⁺ and two acetate ions. [Sigma-Aldrich 940631](https://www.sigmaaldrich.com/US/en/product/aldrich/940631).

A supplied aqueous solution is a composition, not another fixed hydrate formula. **Synthesis:** its salt-equivalent concentration, total nickel concentration, water content, and other constituents are separate quantities. The solid identities above do not establish solution density, free nickel-ion activity, acetate complex fractions, or pH. This reference has no verified equilibrium model for a specified aqueous composition.

## Formula mass and nickel-equivalent content

The following are nonprocedural stoichiometric calculations for ideal pure materials. They use the supplier formula masses above and nickel's standard atomic weight, 58.6934, reported by CIAAW. They are neither measured lot assays nor formulation quantities. [CIAAW nickel](https://ciaaw.org/nickel.htm).

| Calculated quantity | Anhydrous formula basis | Tetrahydrate formula basis |
| --- | --- | --- |
| Nickel mass fraction | 58.6934 / 176.78 = 33.201% | 58.6934 / 248.84 = 23.587% |
| Acetate remainder of the anhydrous formula | (176.78 − 58.6934) / 176.78 = 66.799% | (176.78 − 58.6934) / 248.84 = 47.455% |
| Hydration-water contribution, using the rounded mass difference | None in the ideal formula | (248.84 − 176.78) / 248.84 = 28.958% |
| Anhydrous-salt equivalent per unit tetrahydrate mass | Not applicable | 176.78 / 248.84 = 71.042% |

**Derived limitation:** the ideal tetrahydrate contains about 23.59% nickel by mass even if its salt assay is 100%. A product described as 98% nickel acetate does not thereby contain 98% elemental nickel. Water content, impurity basis, and analytical method determine whether an assay can support a metal-equivalent calculation. The table's water fraction also does not predict the complete mass loss during heating.

## Assay, impurities, and commercial grades

FUJIFILM Wako code 14-0575 illustrates why grade labels need an analytical basis. Its specification gives at least 99.9% purity by a subtracting method and at least 98.0% assay by volumetric analysis. The footnote defines the subtracting method through determination of metal impurities. These two results describe different measurements. A 99.9% headline is not independently a 99.9% volumetric salt assay or a water determination. The sheet's revision footer is 2020-05-21. [Wako specification, complete table and footnote](https://labchem-wako.fujifilm.com/us/product/spec_14-0575.pdf?jeAttribute=E).

Sigma-Aldrich's anhydrous 940631 page separately lists EDTA titration, at least 99.9% trace-metals-basis purity, and a moisture claim below 0.5%. Its listed impurity limits include chloride and sulfate each at most 50 ppm, sodium at most 30 ppm, and iron and lead each at most 10 ppm. Those are product-specific specifications, not generic limits for nickel acetate. [Sigma-Aldrich 940631 properties and product description](https://www.sigmaaldrich.com/US/en/product/aldrich/940631).

Loba Chemie Extra Pure 04864 instead lists an assay marked "ex Ni" of at least 98%, water-insoluble matter at most 0.025%, chloride at most 0.01%, sulfate at most 0.05%, iron at most 0.02%, and lead and zinc each at most 0.005%. The page does not give the full assay calculation or uncertainty. "Ex Ni" is not a claim of 98% elemental nickel. [Loba 04864 specifications](https://www.lobachemie.com/LaboratoryChemicals-04864/NICKEL-ACETATE-TETRAHYDRATE-CASNO-6018-89-9.aspx).

The Consortia profile gives compositional ranges for its registration identity, including 99–100% tetrahydrate and a footnoted category of other impurities. Those ranges define that profile's scope, not every supplier grade. Loba's SDS section 3 identifies a mono-constituent substance. **Synthesis:** neither a registration profile nor SDS composition supplies current-lot water, assay, or trace-element results. No current-lot certificate of analysis was verified here. [Consortia profile](https://www.nickelconsortia.eu/assets/files/consortia/SIPs/2022/Nickel%20Acetate%20-%20updated%20in%202022.pdf), [Loba SDS, section 3](https://www.lobachemie.com/lab-chemical-msds/MSDS-NICKEL-ACETATE-TETRAHYDRATE-CASNO-6018-89-04864-EN.aspx).

## Physical properties and conflicting bases

The tetrahydrate's published density values differ. Sigma-Aldrich 244066 reports 1.798 g/mL at 25 °C as a literature value. Loba's 04864 SDS gives 1.744 g/cm³ without a measurement temperature or method, while its product page gives 1.798 g/cm³. These are solid-product data, not solution or loose-powder bulk densities. The available evidence does not resolve the disagreement. Appearance descriptions also vary within green and blue-green shades. Color alone establishes neither assay nor hydration state. [Sigma-Aldrich 244066](https://www.sigmaaldrich.com/US/en/product/aldrich/244066), [Loba SDS, section 9](https://www.lobachemie.com/lab-chemical-msds/MSDS-NICKEL-ACETATE-TETRAHYDRATE-CASNO-6018-89-04864-EN.aspx), [Loba product page](https://www.lobachemie.com/LaboratoryChemicals-04864/NICKEL-ACETATE-TETRAHYDRATE-CASNO-6018-89-9.aspx).

NOAA's June 1999 CHRIS sheet gives water solubility as 17 pounds per 100 pounds of water at 68 °F, equivalent to 20 °C. **Derived arithmetic:** that denominator corresponds to 17 g per 100 g water, or 17 / 117 = 14.53% solute by combined mass if those are the only components. It is not 17% of final solution and cannot become g/L without a volume basis. The sheet pairs a tetrahydrate formula and 248.86 formula mass with CAS 373-02-4, unlike the form-specific manufacturer identities above. That inconsistency limits transfer of its historical solubility datum. [NOAA CHRIS NKA, sections 2, 9.2, and table 9.24](https://cameochemicals.noaa.gov/chris/NKA.pdf).

Loba's product page labels a solubility field with percent-by-weight units but supplies only a qualitative statement. Neither supports a numerical saturation concentration or a temperature-dependent solubility curve. [Loba product properties](https://www.lobachemie.com/LaboratoryChemicals-04864/NICKEL-ACETATE-TETRAHYDRATE-CASNO-6018-89-9.aspx), [Loba SDS, section 9](https://www.lobachemie.com/lab-chemical-msds/MSDS-NICKEL-ACETATE-TETRAHYDRATE-CASNO-6018-89-04864-EN.aspx).

## Dehydration is distinct from decomposition

Loba's tetrahydrate SDS describes decomposition in its melting-point field without a numerical temperature. NOAA likewise marks the boiling-point field as not pertinent because of decomposition. Neither entry establishes a clean liquid phase or a numerical melting point. [Loba SDS, section 9](https://www.lobachemie.com/lab-chemical-msds/MSDS-NICKEL-ACETATE-TETRAHYDRATE-CASNO-6018-89-04864-EN.aspx), [NOAA CHRIS, section 9.3](https://cameochemicals.noaa.gov/chris/NKA.pdf).

De Jesus and colleagues studied tetrahydrate by thermogravimetry, evolved-gas mass spectrometry, and X-ray photoelectron spectroscopy. Their derivative thermogravimetric dehydration peaks were at 118–137 °C under the studied air, helium, and hydrogen atmospheres. The major subsequent decomposition peaks were near 345–350 °C. Those are experimental peak temperatures, not equilibrium transition points or onset temperatures. The authors found evidence for acetate chemistry during water release, so the intermediate could not be treated as pure anhydrous acetate. Atmosphere affected the residues. **Synthesis:** a dehydration peak, decomposition peak, and SDS melting-field entry describe different evidence. None alone defines a universal thermal constant. [De Jesus et al., 2005, DOI and abstract](https://doi.org/10.1016/j.molcata.2004.09.065), [accessible article text, sections 2.2 and 3.1](https://www.lookchem.com/FreePDFArticle_7440-02-0_8423263.htm).

## Dated hazard evidence and coverage

Loba's English SDS version 1.0, revised 2021-12-20, uses EU CLP classification. It identifies oral and inhalation acute toxicity category 4, respiratory and skin sensitization category 1, germ-cell mutagenicity category 2, inhalation carcinogenicity category 1A, reproductive toxicity category 1B, repeated-exposure organ toxicity category 1, and chronic aquatic hazard category 1. This is dated product-specific classification evidence, not a statement of worldwide legal status or a classification of every solution. [Loba SDS, sections 1–3](https://www.lobachemie.com/lab-chemical-msds/MSDS-NICKEL-ACETATE-TETRAHYDRATE-CASNO-6018-89-04864-EN.aspx).

Research reviewed on 2026-10-30 PDT covers the named solid products and the cited historical measurements. Live product pages have no fixed revision stated here. The Consortia PDF's directory says 2022, but its printed date is 2019-06-05. Wako's downloaded sheet displays 2026-10-31 at the top and a 2020-05-21 revision footer. The top date does not establish a later technical revision. The cited evidence does not establish aqueous speciation, current-lot composition, formulation compatibility, or manufacturing performance.

## Related reference

[Surface-finishing processes](../../processes/finishing/index.md) provides broader terminology. A substance identity does not establish the composition or performance of a proprietary formulation.