A practical guide to copper sulfate, how the pentahydrate and monohydrate forms differ, where each is used, and how to read a specification, from a US-based distributor.
Copper sulfate (CuSO4, CAS 7758-99-8 pentahydrate) is a water-soluble copper salt, familiar as bright blue crystals. It supplies copper as a crop micronutrient and animal feed supplement, and is used in electroplating, mineral flotation, and as a feedstock for other copper compounds. The pentahydrate carries roughly 25% copper; the monohydrate roughly 35%. Stratus Chemical supplies both forms across the United States.
| Property | Value |
|---|---|
| Chemical name | Copper(II) sulfate |
| Synonyms | Cupric sulfate, copper sulphate, blue vitriol, bluestone, Roman vitriol |
| CAS number | 7758-99-8 (pentahydrate), 10257-54-2 (monohydrate), 7758-98-7 (anhydrous) |
| Molecular formula | CuSO4·5H2O, CuSO4·H2O |
| Molecular weight | 249.69 g/mol (pentahydrate), 179.63 g/mol (monohydrate) |
| EC / EINECS | 231-847-6 |
| Appearance | Blue crystals or powder (pentahydrate); pale blue-green powder (monohydrate) |
| Copper content | Approximately 25% (pentahydrate), approximately 35% (monohydrate) |
| Grades supplied | Pentahydrate (crystal / fine), monohydrate (feed grade) |
| Packaging | Bags, supersacks |
| Documentation | COA & SDS provided on request |
Certificates of analysis are provided with each shipment. Tell us your hydrate form, crystal size, and grade requirement and we will confirm what is available.
The figures below are representative of feed and fertilizer grade copper sulfate pentahydrate. They are indicative rather than guaranteed: specifications vary by source and by lot, and the certificate of analysis for your material governs.
| Parameter | Typical value |
|---|---|
| Copper (Cu) | 25.2% min |
| Iron (Fe) | 0.2% max |
| Chloride (Cl) | 500 ppm max |
| Sulfates (SO4) | 0.04% max |
| Lead (Pb) | 70 ppm max |
| Cadmium (Cd) | 70 ppm max |
| MEA insolubles | 0.5% max |
| Packing options | 25 kg bags, 50 lb bags, big bags / totes |
Copper sulfate is the copper salt of sulfuric acid. The pentahydrate is the form most people picture: bright blue triclinic crystals that dissolve readily in water to give a blue solution. Drive off the water and the compound turns white; add water back and the blue returns, which is the classic laboratory demonstration of hydration.
Commercially it is the cheapest and most widely traded soluble copper compound, which makes it the default starting point wherever copper needs to be delivered in solution, whether that is into a soil, a plating bath, or a flotation circuit.
The two commercial hydrates serve different ends of the market.
The pentahydrate, at roughly 25% copper, is the general-purpose form. It is supplied in a range of crystal sizes from large crystal down to fine powder, and the size choice is a dissolution decision: fine material dissolves quickly for tank mixing, while larger crystal resists caking and is easier to handle in bulk.
The monohydrate, at roughly 35% copper, is a free-flowing powder produced by partially dehydrating the pentahydrate. Its higher analysis means less freight per unit of copper, and it resists caking better in dry blends, which is why feed mills and dry fertilizer blenders generally prefer it.
Copper deficiency appears most often on organic and peat soils, on sandy soils, and in cereals, where it causes poor grain fill and characteristic tip dieback. Copper sulfate is applied to soil or as a foliar spray to correct it. Copper has a narrow window between deficiency and toxicity, narrower than most micronutrients, so rates should follow a soil or tissue test rather than a standing prescription. See our crop micronutrients guide for how copper sits alongside the other micronutrients.
Copper is an essential trace mineral in livestock diets, and feed-grade copper sulfate is a standard component of mineral premixes. Species tolerance varies sharply, with sheep notably sensitive to copper accumulation, so inclusion rates are formulated by species rather than applied across the board.
Copper sulfate serves as the copper source in electroplating and electroforming baths, as an activator in mineral flotation, as an etchant in printed circuit manufacture, in leather tanning and pigment production, and as a feedstock for other copper compounds.
| Copper source | How it behaves | Trade-off |
|---|---|---|
| Copper sulfate pentahydrate | Approximately 25% Cu, fully soluble, blue crystal | Cheapest soluble copper, but solutions are acidic and corrosive to mild steel |
| Copper sulfate monohydrate | Approximately 35% Cu, free-flowing powder | Better analysis and handling for dry blends and feed, generally a higher price per ton |
| Copper oxide | High copper analysis, very low water solubility | Cheap per unit copper, but poorly available to plants and slow to release in feed |
| Chelated copper (Cu EDTA) | Copper held in a protective organic complex | Stays available on high-pH soils and is gentler on foliage, but several times the cost per unit copper |
How to choose: for soil-applied copper on neutral to acidic ground, the sulfate is the economical answer and there is little reason to pay for a chelate. On calcareous soils, or where the material goes on the leaf and phytotoxicity is a concern, the chelate delivers more of what is applied and is easier on the crop. For feed, the monohydrate generally wins on analysis and handling; for anything mixed into solution, the pentahydrate dissolves faster.
Store copper sulfate dry in closed original packaging, off damp floors, and away from acids and strong oxidizers. It picks up moisture readily enough that damp bags cake into a solid mass, which is the most common practical complaint about the product.
Copper sulfate solutions are acidic and corrosive to mild steel, galvanized surfaces, and aluminum. Mix and store solutions in plastic or stainless steel, and do not leave solution standing in carbon steel equipment.
The material is highly toxic to aquatic organisms, and this is the dominant environmental hazard. Contain spills, keep material away from drains, ditches, and surface water, and do not rinse equipment where the washings can reach a watercourse. Handle dust with the eye and respiratory protection specified in the Safety Data Sheet.
Copper sulfate is used as a copper micronutrient in crop nutrition, as a copper supplement in animal feed, and in industrial applications including electroplating, mineral flotation, and as a raw material for other copper compounds. Stratus Chemical supplies pentahydrate and monohydrate forms in bags and supersacks across the United States.
Copper sulfate has a different CAS number for each hydrate. The pentahydrate, the most common commercial form, is 7758-99-8. The monohydrate is 10257-54-2 and the anhydrous form is 7758-98-7. Copper sulfate carries EC number 231-847-6. The pentahydrate has a molecular weight of 249.69 g/mol.
The difference is water of crystallization and therefore copper concentration. The pentahydrate contains approximately 25% copper and is the familiar blue crystal, readily soluble and the standard form for agricultural and industrial solution use. The monohydrate contains approximately 35% copper, is a pale free-flowing powder, and is favored in animal feed and dry blends because it delivers more copper per ton and does not cake as readily.
Copper sulfate pentahydrate contains approximately 25% copper and the monohydrate approximately 35%, based on the stoichiometry of the pure compounds. Commercial grades vary around those figures with assay and moisture, so work from the guaranteed analysis on the certificate of analysis for the lot rather than a theoretical figure.
A representative feed and fertilizer grade copper sulfate pentahydrate specification runs copper at 25.2% minimum, iron at 0.2% maximum, chloride at 500 ppm maximum, sulfates at 0.04% maximum, lead and cadmium each at 70 ppm maximum, and MEA insolubles at 0.5% maximum. Specifications vary by source and lot, so always confirm against the certificate of analysis for the material you are quoted.
Store copper sulfate dry in closed original packaging, off damp floors and away from acids. It is hygroscopic enough that damp bags cake, and its solutions are acidic and corrosive to mild steel and galvanized surfaces, so use plastic or stainless equipment for mixing and storage. Copper sulfate is highly toxic to aquatic life, so contain spills and keep material out of drains and surface water. Follow the Safety Data Sheet for dust and skin exposure controls.
Stratus Chemical supplies copper sulfate in bags and supersacks, as pentahydrate in crystal and fine grades and as feed grade monohydrate, with a certificate of analysis provided for each shipment. Tell us the hydrate form, crystal size, grade, and volume and we will confirm pricing and availability within one business day.
Building a micronutrient program? See zinc sulfate and the crop micronutrients guide, or the full agriculture range. Looking for something else? Browse all products or request a quote.
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