What is Copper Sulphate and Why is it Called Blue Vitriol?
Copper sulphate (CuSO₄) is essential in chemistry and helps students understand various practical and theoretical applications related to this topic. This salt is one of the most common compounds discussed in inorganic chemistry due to its striking blue color, unique chemical behavior, and wide usage in laboratories, industry, and agriculture. Learning about copper sulphate helps you master the concepts of ionic compounds, redox reactions, salt preparations, and their distinct physical properties.
What is Copper Sulphate (CuSO₄) in Chemistry?
A copper sulphate refers to an inorganic salt with the chemical formula CuSO₄. This compound typically exists as blue vitriol or copper(II) sulphate pentahydrate (CuSO₄·5H₂O). This concept appears in chapters related to salt analysis, redox reactions, and hydrated compounds, making it a foundational part of your chemistry syllabus. Copper sulphate is known for forming characteristic blue crystals due to water of hydration and serves as a key example for recognizing transition metal salts and their color changes during chemical reactions.
Molecular Formula and Composition
The molecular formula of copper sulphate is CuSO₄. It consists of a copper(II) cation (Cu²⁺) and a sulphate anion (SO₄²⁻) and is categorized under ionic salts. The most common form – pentahydrate copper sulphate – is written as CuSO₄·5H₂O, meaning five water molecules are incorporated into each formula unit. The hydrated blue color is a result of these water molecules bound to the copper center.
| Property | Anhydrous CuSO₄ | Hydrated CuSO₄·5H₂O |
|---|---|---|
| Appearance | White powder | Bright blue crystals |
| Molar Mass (g/mol) | 159.61 | 249.68 |
| Solubility in water | High | High |
Preparation and Synthesis Methods
Both laboratory and industrial methods are used to prepare copper sulphate. In the lab, copper sulphate crystals are usually made by reacting copper metal with dilute sulphuric acid and heating in the presence of air:
1. Place copper turnings in a beaker.
2. Add dilute sulphuric acid.
3. Warm the mixture; copper slowly dissolves as blue solution forms:
4. Filter and allow to cool for blue crystals to form.
Industrially, copper sulphate is made by dissolving copper scrap or metal in hot, dilute sulphuric acid with oxygen, or by roasting copper ores and dissolving the resulting copper oxide in sulphuric acid.
Physical Properties of Copper Sulphate (CuSO₄)
Copper sulphate displays characteristic physical properties that make it easy to identify:
- Appearance: White (anhydrous), Bright blue (pentahydrate)
- Solubility: Highly soluble in water
- Odor: Odorless
- Density: 3.6 g/cm³ (anhydrous), 2.28 g/cm³ (pentahydrate)
- Melting Point: Decomposes at ~110°C (pentahydrate loses water turning white)
Chemical Properties and Reactions
Copper sulphate (CuSO₄) performs typical reactions of transition metal salts and is involved in many redox and displacement reactions:
- Displacement Reaction with Iron: Fe (s) + CuSO₄ (aq) → FeSO₄ (aq) + Cu (s)
- Reaction with Zinc: Zn (s) + CuSO₄ (aq) → ZnSO₄ (aq) + Cu (s)
- Reaction with Sodium Hydroxide: Forms a blue precipitate of Cu(OH)₂:
CuSO₄ (aq) + 2 NaOH (aq) → Cu(OH)₂ (s) + Na₂SO₄ (aq) - Thermal Decomposition: On heating, hydrated CuSO₄ turns from blue to white as it loses water of crystallization.
Frequent Related Errors
- Confusing copper sulphate with copper(I) sulphate (Cu₂SO₄), which is rarely encountered.
- Assuming blue color is due to sulphate alone, when it is due to hydrated copper(II) ions.
- Ignoring the change from blue (hydrated) to white (anhydrous) as a test for water.
- Mixing up displacement reactions: only metals above copper in the reactivity series can displace it from CuSO₄ solutions.
Uses of Copper Sulphate in Real Life
Copper sulphate is widely used in industries like agriculture, education, mining, and textiles. It is a vital fungicide and algicide in farming, a blue pigment in dyes, and an electrolyte in copper refining. In chemistry labs, it is a standard reagent for testing water and in salt analysis. Even in education, qualitative analysis experiments use copper sulphate to teach concepts like displacement and crystallization. Many crystallization experiments grow blue vitriol crystals for students to observe. This compound also finds use in manufacturing other chemicals and in electroplating processes.
Relevance in Competitive Exams
Students preparing for NEET, JEE, and Olympiads should be familiar with copper sulphate, as it often features in reaction-based and concept-testing questions. These can include distinguishing between hydrated and anhydrous compounds, predicting displacement reactions, and linking salt color to transition metal complexes. Practical-based sections may ask about safe handling or the preparation and identification of copper salts. Many questions also test the redox behavior of copper compounds, including their use in batteries (like the Daniell cell) and redox reactions.
Relation with Other Chemistry Concepts
Copper sulphate is closely related to topics such as displacement reactions and anhydrous salts, helping students build a conceptual bridge between various chapters. It is also important while studying hydrated vs. anhydrous compounds, electrolytic reactions, and qualitative salt analysis. Understanding copper sulphate’s structure and reactions reinforces lessons on ionic bonding, coordination, and changes of state.
Step-by-Step Reaction Example
Example: Displacement of Copper by Iron from Copper Sulphate Solution
1. Setup: Add iron nail to a CuSO₄ solution.2. Balanced equation: Fe (s) + CuSO₄ (aq) → FeSO₄ (aq) + Cu (s)
3. Iron (more reactive) displaces copper from the blue solution.
4. Blue color fades as iron(II) sulphate (pale green) forms and copper metal deposits as a brown layer.
5. Conclude: This demonstrates displacement and redox principles.
Lab or Experimental Tips
Remember copper sulphate by the “blue for water” rule—blue crystals always mean water is present (hydrated salt), while the powdery white form is anhydrous. Vedantu educators often use this tip in live sessions to simplify complex concepts and to connect visual color changes with chemical transformations in salt analysis labs.
Try This Yourself
- Write the IUPAC name of CuSO₄·5H₂O.
- Identify if copper sulphate is acidic, basic, or neutral in aqueous solution.
- Give two real-life examples where copper sulphate is used in daily life or industry.
Final Wrap-Up
We explored copper sulphate (CuSO₄)—its structure, properties, reactions, and real-life importance. It stands as one of the best examples for understanding chemical color, salt preparation, redox, and industrial chemistry. For more in-depth explanations and exam-prep tips, explore live classes and notes on Vedantu. Practicing the reactions and remembering the visual cues will help you master salt analysis and related chapters in chemistry with ease.
Related topics for further reading:
Qualitative Analysis of Copper Compounds |
Displacement Reactions |
Redox Reactions | Crystallization
FAQs on Copper Sulphate (CuSO₄) Explained: Structure, Properties, and Applications
1. Why is copper sulphate called blue vitriol?
Copper sulphate is commonly called blue vitriol because its pentahydrate form, CuSO4·5H2O, forms bright blue crystals. This blue color is due to the presence of water molecules (water of hydration) coordinated to the copper(II) ion.
2. What is the chemical formula and structure of copper sulphate?
The chemical formula for copper sulphate is CuSO4. The most common form is the pentahydrate, CuSO4·5H2O, where one copper(II) ion is coordinated to one sulfate ion and five water molecules. The structure involves a distorted octahedral geometry around the copper ion.
3. What happens when copper sulphate reacts with iron?
Iron (Fe) is more reactive than copper (Cu), so it displaces copper from copper sulphate solution in a redox reaction. The reaction is: Fe(s) + CuSO4(aq) → FeSO4(aq) + Cu(s). This results in the formation of iron(II) sulphate and metallic copper.
4. How is copper sulphate used in agriculture?
Copper sulphate is used in agriculture as a fungicide and algicide to control fungal and algal growth. It's also a source of copper, an essential micronutrient for plant health, and is applied to copper-deficient soils.
5. Is copper sulphate toxic?
Yes, copper sulphate is toxic if ingested or inhaled in large amounts. It can cause irritation to the skin, eyes, and respiratory tract. Always handle copper sulphate with care and follow safety precautions.
6. Why does heating blue vitriol turn it white?
Heating blue vitriol (CuSO4·5H2O) drives off the five water molecules of hydration. This conversion from the pentahydrate to the anhydrous form, CuSO4, results in a color change from blue to white.
7. How is copper sulphate used in qualitative laboratory tests?
Copper sulphate can be used in qualitative analysis to test for the presence of certain substances. For example, it can be used in the Benedict's test for reducing sugars, where a change in color signifies a positive result.
8. What are alternative names for copper sulphate?
Besides copper sulphate, other names include blue vitriol, cupric sulphate, and copper(II) sulfate.
9. What happens if you mix copper sulphate with sodium hydroxide?
Mixing copper sulphate with sodium hydroxide (NaOH) produces a precipitation reaction. A pale blue precipitate of copper(II) hydroxide, Cu(OH)2, forms.
10. Can you write a balanced equation for the reaction of copper sulphate and zinc?
The balanced equation for the reaction of copper sulphate with zinc (Zn) is: Zn(s) + CuSO4(aq) → ZnSO4(aq) + Cu(s). This is a single displacement reaction.
11. What are the industrial uses of copper sulphate?
Copper sulphate has several industrial applications, including use as an electrolyte in electroplating and refining copper, a component in anti-fouling paints, and in the production of certain pigments and dyes.
12. How is copper sulphate prepared?
Copper sulphate can be prepared by reacting copper metal with dilute sulfuric acid in the presence of oxygen. Alternatively, it can be prepared by reacting copper(II) oxide or copper(II) carbonate with sulfuric acid.
