Nickel sulfate

Identity and forms

Ideal nickel(II) sulfate hexahydrate contains 22.33% nickel by mass. The heptahydrate contains 20.90% and anhydrous NiSO₄ 37.93%. These are formula equivalents. Delivered metal content requires a lot-specific result or a conversion supported by the lot assay and hydrate basis. Anhydrous NiSO₄ pairs nickel and sulfate ions 1:1. Sigma-Aldrich 656895

Sources: Sigma-Aldrich anhydrous identity, Thermo Fisher hexahydrate certificate, Sigma-Aldrich heptahydrate identity.

The hydrate formula includes a defined amount of crystal water. A liquid product has a separate composition. Atotech's historical LIQUID NICKEL SULFATE (CI), product 2202745, is described as a nickel salt mixture. Its revision 2 MSDS, dated April 19, 2006, lists 40–50% by weight nickel(II) sulfate hexahydrate, CAS 10101-97-0. The disclosure note allows unlisted components below the stated disclosure criteria. This is an ingredient range for that historical mixture, not a complete formulation or evidence of its present availability. Atotech MSDS, sections 1 and 3, hosted by Hill Brothers

Synthesis: a hydrate CAS number in a liquid-product ingredient table does not establish intact hydrate crystals or discrete hydrate molecules in the liquid. Formulas used for composition accounting and the species actually present in solution answer different questions.

Assay, purity basis, and lot evidence

Merck EMPLURA 106726 specifies a complexometric assay of at least 98.0%. Selected limits are chloride ≤0.003%, cobalt ≤0.05%, iron ≤0.01%, lead ≤0.001%, and zinc ≤0.2%. The page does not give a separate water result. These limits describe this product, not every commercial hexahydrate. Merck 106726 specification

A public Thermo Fisher certificate for analytical hexahydrate 21108, lot A0461345, was released March 20, 2024. It distinguishes specification limits from the reported test values.

The certificate does not state the ppm denominator, a separate water determination, or a detailed titration calculation. Its 100.4% assay is an analytical result, not a literal mass fraction above unity. The cause of the excess above 100% is not established here. This certificate supports one named lot, not a current shipment or every product sold as analytical grade. Thermo Fisher certificate, complete table and qualification text

Sigma-Aldrich 203890 is labeled 99.999% on a trace metals basis. The same page separately lists a trace metal analysis limit of ≤15 ppm. Those two statements are retained as published. Their analytical denominators and reconciliation are not explained on the page. A trace metals purity claim does not establish the fraction of crystal water or all nonmetal impurities. Sigma-Aldrich 203890

Synthesis: nickel content, hydrate-equivalent assay, water content, and impurity limits are distinct quantities. Grade names alone do not establish interchangeability. An SDS composition range is also different from a specification limit or a measured lot result. No certificate tied to a reader's current material was examined.

Nickel and salt-equivalent mass bases

The following nonprocedural calculations describe ideal formula compositions. They use 58.6934 g/mol for nickel, from CIAAW's standard atomic weight, and the formula masses in the identity table. They are composition arithmetic, not preparation quantities. CIAAW nickel, anhydrous formula mass, hexahydrate formula mass, heptahydrate formula mass

Derived relationship: one unit of nickel mass corresponds to about 2.637 units of NiSO₄-equivalent mass, or 4.478 units of hexahydrate-equivalent mass. These relationships assume that all counted nickel belongs to the stated nickel sulfate component. They do not measure water, free acid, other nickel compounds, or impurities.

A mass percentage means grams per 100 g of the stated material. A value in g/L needs an explicit chemical basis and a volume denominator. Conversion between mass percentage and g/L also needs solution density at the relevant temperature. Crystal density and powder bulk density do not provide solution density.

Physical properties and thermal distinctions

Sources: Merck properties, Sigma-Aldrich heptahydrate properties, ICSC 0063, April 2017.

Bulk density includes spaces between particles. The Merck page does not specify a packing method. Its solubility entry is 650 g/L, without temperature or an explicit solvent-versus-final-solution volume denominator. ICSC 0063 gives 29.3 g/100 mL at 20 °C for NiSO₄, also without an explicit volume denominator. The different chemical bases and incomplete conditions prevent treating these entries as a measured solubility disagreement or one interchangeable limit. Merck properties, ICSC physical information

ICSC 0063 states that crystal water is gradually released at temperatures up to 330 °C. It separately reports decomposition of NiSO₄ at 848 °C and explicitly gives no melting point. Those entries distinguish loss of hydrate water from decomposition of the sulfate. They do not establish a heating schedule or an equilibrium boundary between hydrate crystal phases. ICSC notes and physical information

King and Mahapatra's 2022 original research abstract describes simultaneous thermogravimetry and differential scanning calorimetry in flowing air, with X-ray diffraction of the solid products. It reports dehydration of the investigated nickel salt hydrates within 100–350 °C and anhydrous NiSO₄ decomposition at 810 °C. The 810 °C result and the card's 848 °C entry remain separate. Their difference is unresolved here because the full research article is subscription restricted and the card supplies no comparable thermal method. Neither number is a universal melting point. King and Mahapatra, publisher abstract

Aqueous species and appearance

Chen, Hefter, and Buchner's 2005 research abstract reports dielectric relaxation measurements of nickel(II) sulfate solutions at 25 °C over 0.025–1.4 mol/L. The spectra indicate simultaneous double solvent-separated, solvent-shared, and contact ion pairs. The abstract supports ion association within that study's conditions, not one universal species fraction for all solutions. Author-affiliated repository abstract

Synthesis: a formula-equivalent concentration is not automatically the concentration or activity of free Ni²⁺. The cited abstract does not establish species fractions for mixtures containing other salts or complexing ingredients. Color is not a quantitative assay, an impurity result, or evidence of process performance.

Hazard and source scope

The Atotech MSDS identifies United States and Canadian suppliers and uses the OSHA and WHMIS frameworks of its April 19, 2006 revision. It identifies irritation, harmful effects if swallowed, allergic skin and respiratory effects, and aquatic toxicity. Those statements apply to that historical liquid product and document version. They do not establish its present regional classification. Atotech MSDS, sections 1–3

The April 2017 ILO/WHO card identifies inhalation carcinogenicity, reproductive hazard, sensitization, and severe aquatic hazard. Its notes extend the recommendations to the hexahydrate and heptahydrate. The card is an international hazard reference, not a jurisdiction-specific compliance determination. Hazard evidence does not establish purity or manufacturing performance. ICSC 0063 classification and notes

The supplier pages are undated and were consulted on October 30, 2026 PDT. Coverage includes one historical liquid MSDS, one named reagent lot, and selected supplier properties. Full thermal and aqueous research articles were unavailable; claims from those studies are limited to their public abstracts. Verified equilibrium hydrate-transition boundaries, complete solubility curves, current regional product SDSs, current lot water measurements, and mixture-specific speciation remain outside this reference. No customer material suitability, production settings, or global regulatory status follows from these sources.

Related reference

Surface-finishing processes describes the broader process family.