Molar Mass of Copper(II) Sulfate (CuSO₄)
Learn how chemists calculate the molar mass of Copper(II) Sulfate (CuSO₄), with a clear formula breakdown, worked steps, and study notes · IUPAC name: Copper(II) sulfate.
Quick answer
The molar mass of Copper(II) Sulfate (CuSO₄) is
159.602g/mol
One mole of Copper(II) Sulfate therefore has a mass of 159.602 grams—the value you use for stoichiometry and laboratory preparation.
Reviewed for educational accuracy · Accuracy policy
- CAS Registry Number
- 7758-98-7
- PubChem CID
- 24462
- SMILES
- [Cu+2].[O-]S(=O)(=O)[O-]
Step-by-step calculation
Let's find the molar mass of Copper(II) Sulfate (CuSO₄) together—step by step, as if you are seeing the formula for the first time.
Step 1 — Look at the chemical formula
The formula is CuSO₄. Each letter stands for an element. The little number after a letter (the subscript) tells you how many atoms of that element are in one molecule or formula unit.
- 1 Copper atom (Cu)
- 1 Sulfur atom (S)
- 4 Oxygen atoms (O)
Step 2 — Look up each atomic mass
Atomic mass comes from the periodic table. It is the average mass of one mole of atoms of that element, in grams per mole (g/mol). Think of it as the "price tag" for one mole of that element.
- Copper (Cu) = 63.546 g/mol
- Sulfur (S) = 32.060 g/mol
- Oxygen (O) = 15.999 g/mol
Step 3 — Multiply atoms × atomic mass
Why multiply? If one oxygen atom "costs" about 16 g/mol, then two oxygen atoms cost twice as much. Each element's contribution is: number of atoms × atomic mass.
- 1 × 63.546 = 63.546 g/mol (Copper)
- 1 × 32.060 = 32.060 g/mol (Sulfur)
- 4 × 15.999 = 63.996 g/mol (Oxygen)
Step 4 — Add the contributions
Why add? The molar mass of the whole compound is simply the total mass of every atom in the formula. Add each element's contribution:
63.546 + 32.060 + 63.996 = 159.602 g/mol
Step 5 — Final answer
Molar mass of Copper(II) Sulfate = 159.602 g/mol
That means one mole of Copper(II) Sulfate (CuSO₄) has a mass of about 159.60 grams.
Quick summary
Read the formula → count atoms → look up atomic masses → multiply → add → report g/mol. For CuSO₄, the total is 159.602 g/mol.
Common beginner mistakes
- Using anhydrous molar mass (159.62) when given pentahydrate mass in problems.
- Forgetting to include 5 H₂O in hydrate molar mass calculations.
- Assuming CuSO₄ solution is green — it's blue from [Cu(H₂O)₆]²⁺.
Memory trick
Hydrate formula: add 5 × 18 = 90 to 160 ≈ 250 g/mol for pentahydrate.
Mini practice
Without looking above, list the atoms in CuSO₄ and write one multiplication line for the heaviest element. Then check your work against Step 3.
Real-world example
If a recipe asks for 0.100 mol of Copper(II) Sulfate, mass needed = 0.100 × 159.602 = 15.960 g. That is how chemists turn a mole amount into a weighable sample.
Atomic contribution table
Each row shows how much mass one element contributes to the total for CuSO₄.
| Element | Atoms | Atomic mass | Contribution | Mass % |
|---|---|---|---|---|
| Cu | 1 | 63.546 | 63.546 g/mol | 39.8% |
| S | 1 | 32.060 | 32.060 g/mol | 20.1% |
| O | 4 | 15.999 | 63.996 g/mol | 40.1% |
| Total molar mass | 159.602 g/mol | 100% | ||
Mass contribution chart
Teal and blue circles alternate like positive and negative ions in a crystal lattice. Formula mass is the mass of one formula unit, not a single molecule.
Download study sheets
Save a printable summary, revision sheet, practice worksheet, or laboratory reference for Copper(II) Sulfate (CuSO₄).
Practice this calculation
Without looking above, write the atom count for CuSO₄, then compute the molar mass. Check your answer against 159.602 g/mol.
Next challenge: how many grams are in 0.250 mol of Copper(II) Sulfate? Multiply 0.250 × 159.602 to get 39.901 g.
Physical and chemical properties
Physical properties
| Appearance | Blue crystals (pentahydrate); white/off-white powder (anhydrous) |
| Color | Blue (pentahydrate); white (anhydrous) |
| Odor | Odorless |
| State (STP) | Solid |
| Density | 2.28 g/cm³ (pentahydrate); 3.60 g/cm³ (anhydrous) |
| Melting point | 110 °C (pentahydrate, loses water); 650 °C decomposes (anhydrous) |
| Boiling point | Decomposes before boiling |
| Solubility | 320 g/L water at 20 °C (pentahydrate); increases with temperature |
| Crystal structure | Triclinic (pentahydrate); orthorhombic (anhydrous) |
Chemical properties
| Classification | Transition metal sulfate salt |
| Family | Copper(II) salts / transition metal sulfates |
| Polarity | Ionic |
| Oxidation states | Cu: +2, S: +6, O: −2 |
Applications
Industrial uses
- Agricultural fungicide and herbicide (Bordeaux mixture with lime)
- Electroplating and copper refining electrolyte
- Algae control in swimming pools and reservoirs
- Textile mordant in dyeing
Laboratory uses
- Electrolysis demonstrations (Hofmann voltameter)
- Analytical reagent for moisture detection (anhydrous → blue)
- Source of Cu²⁺ for coordination chemistry
- Fehling's solution component (with sodium tartrate)
Copper toxicity to aquatic organisms limits agricultural runoff; used in bioremediation of algae blooms at controlled doses.
Essential trace copper nutrient in small amounts; toxic at higher concentrations — Wilson's disease involves copper accumulation.
Preparation and production
React copper(II) oxide or copper metal with hot dilute sulfuric acid: CuO + H₂SO₄ → CuSO₄ + H₂O. Crystallize pentahydrate from solution. Anhydrous form by heating pentahydrate to ~250 °C (above 150 °C loses water stepwise).
Industrial production from copper scrap or ore leaching with H₂SO₄, followed by crystallization or electrowinning.
Important reactions of Copper(II) Sulfate
Fe(s) + CuSO₄(aq) → FeSO₄(aq) + Cu(s)
- Reaction type
- Single displacement
- Conditions
- Aqueous, room temperature
- Explanation
- Iron, more reactive than copper, displaces Cu²⁺ from solution; copper metal plates out with characteristic red-brown color.
- Products
- Iron(II) sulfate and copper metal
- Why it matters
- Demonstrating activity series, copper recovery
Related ideas: Activity series · Redox · Displacement reactions
CuSO₄(aq) + 2 NaOH(aq) → Cu(OH)₂(s) + Na₂SO₄(aq)
- Reaction type
- Precipitation
- Conditions
- Aqueous, dilute NaOH
- Explanation
- Pale blue Cu(OH)₂ gel precipitates; on heating decomposes to black CuO.
- Products
- Copper(II) hydroxide
- Why it matters
- Qualitative test for Cu²⁺, preparation of CuO
Related ideas: Precipitation · Transition metal hydroxides
CuSO₄(aq) + 4 NH₃(aq) → [Cu(NH₃)₄]SO₄(aq)
- Reaction type
- Complex ion formation
- Conditions
- Excess concentrated ammonia
- Explanation
- Deep blue-violet tetraamminecopper(II) complex forms as NH₃ replaces H₂O ligands — used in qualitative analysis.
- Products
- Tetraamminecopper(II) sulfate
- Why it matters
- Qualitative analysis for Cu²⁺, coordination chemistry
Related ideas: Complex ions · Ligand exchange · Coordination chemistry
CuSO₄·5H₂O(s) → CuSO₄(s) + 5 H₂O(g)
- Reaction type
- Dehydration (thermal)
- Conditions
- Heat to 150–250 °C
- Explanation
- Water of crystallization driven off; white anhydrous CuSO₄ forms; rehydration restores blue color — water test.
- Products
- Anhydrous copper(II) sulfate and water vapor
- Why it matters
- Moisture detection, desiccation, teaching hydrates
Related ideas: Hydrates · Water of crystallization · Thermal analysis
History and discovery
Known since antiquity as blue vitriol from roasting copper ores with sulfur. Used medicinally (emetic) and in alchemy. Modern chemistry established hydration state and [Cu(H₂O)₆]²⁺ structure through spectroscopy and crystallography.
Known to ancient civilizations; systematic study of pentahydrate composition by Proust and others in 18th–19th centuries.
Interesting facts
- Anhydrous CuSO₄ (159.62 g/mol) is white; pentahydrate (249.69 g/mol) is blue — dramatic color change on hydration.
- The five water molecules in CuSO₄·5H₂O contribute 90.10 g/mol to the hydrate molar mass.
- Bordeaux mixture (CuSO₄ + Ca(OH)₂) has been used as fungicide since 1885 in French vineyards.
- Copper sulfate crystals grow into characteristic oblique rhombic shapes in saturated solutions.
Comparison with similar compounds
Anhydrous CuSO₄ (159.62 g/mol) vs. pentahydrate (249.69 g/mol) — same copper content per mole of Cu, but different total mass and color.
Storage, handling, and safety
Store pentahydrate in closed containers — slowly effloresces in dry air. Anhydrous form in sealed desiccator — hygroscopic. Avoid contact with iron (displacement reaction).
Harmful if swallowed; irritant to eyes and skin. Wash hands after handling agricultural formulations. Do not dispose of large quantities in waterways.
Harmful if ingested; irritant to eyes and respiratory tract. Aquatic toxin. Anhydrous form causes thermal burn on hydration with skin moisture.
- Harmful if swallowed (copper toxicity)
- Eye and skin irritation
- Environmental hazard to aquatic life
- Exothermic hydration of anhydrous form
Classification: GHS: Acute Tox. 4 (oral), Aquatic Acute 1
Exam notes and student tips
Exam notes
- Molar mass anhydrous CuSO₄ = 63.55 + 32.07 + 4(16.00) = 159.62 g/mol.
- Molar mass pentahydrate CuSO₄·5H₂O = 159.62 + 5(18.016) = 249.69 g/mol.
- Electrolysis: cathode Cu deposited, anode possibly O₂ (from water) with inert electrodes.
- Fe + CuSO₄ → FeSO₄ + Cu (single displacement, calculate moles Cu produced).
Student tips
- Hydrate formula: add 5 × 18 = 90 to 160 ≈ 250 g/mol for pentahydrate.
- Water of crystallization: heat 250 g hydrate → lose 90 g water → 160 g anhydrous.
- Link blue color to d-d transitions in Cu²⁺ (d⁹ system).
Common mistakes
- Using anhydrous molar mass (159.62) when given pentahydrate mass in problems.
- Forgetting to include 5 H₂O in hydrate molar mass calculations.
- Assuming CuSO₄ solution is green — it's blue from [Cu(H₂O)₆]²⁺.
Misconceptions
- All copper compounds are blue — CuO is black, Cu₂O is red.
- CuSO₄ and copper metal have same toxicity route — sulfate salt has different bioavailability.
- The pentahydrate formula means water is inside as liquid — it's coordinated in crystal lattice.
Practice questions
1. Calculate the molar mass of anhydrous CuSO₄.
Show answer
63.55 + 32.07 + 4(16.00) = 159.62 g/mol
2. What is the molar mass of CuSO₄·5H₂O?
Show answer
159.62 + 5(18.016) = 249.69 g/mol
3. What mass of copper from 159.6 g CuSO₄ reacted with excess Fe?
Show answer
159.6 g ≈ 1 mol CuSO₄ → 1 mol Cu = 63.55 g
4. What percent by mass is water in CuSO₄·5H₂O?
Show answer
90.08/249.69 × 100 = 36.1%
Frequently asked questions about Copper(II) Sulfate
159.62 g/mol (anhydrous CuSO₄); 249.69 g/mol for pentahydrate CuSO₄·5H₂O.
Chemistry of Copper(II) Sulfate
The sections above give the number you need for calculations. Here we look more closely at how Copper(II) Sulfate (CuSO₄) behaves chemically—so the molar mass connects to real reactions, properties, and laboratory practice.
Copper(II) sulfate (CuSO₄) is an ionic compound with molar mass 159.62 g/mol (Cu 63.55 + S 32.07 + 4 × 16.00) in its anhydrous form. The familiar pentahydrate CuSO₄·5H₂O (blue vitriol) has molar mass 249.69 g/mol and forms brilliant blue triclinic crystals where four water molecules coordinate to Cu²⁺ in square planar geometry and one water is hydrogen-bonded in the lattice.
CuSO₄(aq) is the classic solution for the Hofmann voltameter electrolysis demonstration and for electroplating copper. The deep blue [Cu(H₂O)₆]²⁺ hexaaquacopper(II) ion gives aqueous solutions their color; adding ammonia displaces water ligands to form intense blue-violet [Cu(NH₃)₄(H₂O)₂]²⁺ (tetraamminecopper(II)). Anhydrous white CuSO₄ rehydrates exothermically — a test for water used in desiccators and organic chemistry.
CuSO₄ contains Cu²⁺ and SO₄²⁻ in 1:1 ratio. The pentahydrate formula CuSO₄·5H₂O indicates five water molecules per formula unit — four are ligands, one is lattice water. Anhydrous vs. hydrated forms have different molar masses and colors but same Cu:SO₄ ratio.
CuSO₄ dissolves in water giving blue solutions. It undergoes displacement with iron: Fe + CuSO₄ → FeSO₄ + Cu (copper plates out). With ammonia, deep blue complex forms. With NaOH, pale blue Cu(OH)₂ precipitates, turning brown (CuO) on heating. With KI, produces white CuI and brown I₂. Anhydrous form is Lewis acid toward water.
The hydrate molar mass teaching point
Copper sulfate is one of the most common compounds used to teach water-of-crystallization calculations because its color change is so visually dramatic: anhydrous CuSO₄ (159.62 g/mol) is white, while the pentahydrate CuSO₄·5H₂O (249.69 g/mol) is deep blue. Heating a known mass of blue crystals to constant white mass lets students directly measure the 90.10 g/mol contributed by five water molecules, making the hydrate/anhydrate mass difference a hands-on, visually confirmable experiment rather than an abstract calculation.
Bordeaux mixture and agricultural fungicide chemistry
Copper(II) sulfate mixed with hydrated lime (calcium hydroxide) forms Bordeaux mixture, one of the oldest and most widely used agricultural fungicides, protecting grapevines, potatoes, and other crops from fungal blight since its accidental discovery in 1885 by French botanist Pierre-Marie-Alexis Millardet. The mixture releases Cu²⁺ ions slowly, which disrupt fungal spore enzymes without excessive phytotoxicity to the treated plants at proper dosing.
Electroplating and electrorefining electrolyte chemistry
Aqueous CuSO₄ serves as the standard electrolyte for copper electroplating and electrorefining, where Cu²⁺ ions are reduced and deposited as pure metallic copper at the cathode while impure copper dissolves as Cu²⁺ at the anode, a process that purifies over 99% of the world's refined copper and deposits decorative or protective copper coatings in electronics and jewelry manufacturing.
The distinctive blue color and d-d electronic transitions
The intense blue of dissolved copper sulfate arises from the hexaaquacopper(II) ion, [Cu(H₂O)₆]²⁺, in which the d⁹ electron configuration of Cu²⁺ allows visible-light-driven d-d electronic transitions that absorb red-orange wavelengths and transmit blue — a concrete, memorable example of transition metal coordination chemistry and crystal field theory that instructors frequently use to introduce the color of transition metal complexes.
Recalculate any formula with the molar mass calculator, compare atoms on the periodic table, or browse more compounds in the salt library.
References and further reading
- PubChem CID 24462: Copper(II) sulfate data
- NIST Chemistry WebBook: Thermodynamic properties
- Royal Society of Chemistry: Copper sulfate education resources