How is Copper Hydroxide Prepared in the Laboratory?
Copper hydroxide is essential in chemistry and helps students understand various practical and theoretical applications related to this topic. From school science experiments to real-world applications in agriculture, copper hydroxide plays a crucial role in the chemistry of transition metals, color changes, and everyday chemical processes.
What is Copper Hydroxide in Chemistry?
A copper hydroxide refers to an inorganic compound with the chemical formula Cu(OH)2. This bluish solid forms when copper(II) salts react with hydroxide ions and is recognized as a classic example of a transition metal hydroxide. This concept appears in chapters related to precipitation reactions, transition metals, and acid-base chemistry, making it a foundational part of your chemistry syllabus.
Molecular Formula and Composition
The molecular formula of copper hydroxide is Cu(OH)2. It consists of one copper ion (Cu2+) bonded to two hydroxide (OH-) ions. This compound is categorized under inorganic bases and transition metal hydroxides.
Preparation and Synthesis Methods
In the laboratory, copper hydroxide is typically prepared by mixing a soluble copper(II) salt (like copper sulfate) with an alkaline solution such as sodium hydroxide. The reaction forms a distinctive blue precipitate of copper hydroxide, which is sparingly soluble in water. Industrially, it can be obtained as a by-product in copper processing or created for specific uses like fungicides.
CuSO4 (aq) + 2 NaOH (aq) → Cu(OH)2 (s) + Na2SO4 (aq)
Physical Properties of Copper Hydroxide
- Appearance: Blue, gelatinous solid
- State: Solid at room temperature
- Solubility: Insoluble in water; slightly dissolves in ammonia or strong alkalis
- Molar Mass: 97.56 g/mol
- Odor: Odorless
- pH: Basic/alkaline
| Property | Value |
|---|---|
| Formula | Cu(OH)2 |
| Color | Blue |
| Molar Mass | 97.56 g/mol |
| Solubility in Water | Very low (forms precipitate) |
| Classification | Inorganic, transition metal hydroxide, base |
Chemical Properties and Reactions
Copper hydroxide shows several interesting chemical reactions:
1. Double Displacement Reaction (precipitation):CuSO4 + 2 NaOH → Cu(OH)2 (blue ppt) + Na2SO4
2. Decomposition on Heating:
Cu(OH)2 (s) → CuO (s) [black] + H2O (l)
3. Reaction with Acids (neutralization):
Cu(OH)2 + 2 HNO3 → Cu(NO3)2 + 2 H2O
4. With excess ammonia, forms a deep blue solution due to complex ion formation:
Cu(OH)2 + 4 NH3 (aq) → [Cu(NH3)4]2+ + 2 OH-
5. Mildly amphoteric—dissolves slightly in strong alkali to give complex anions.
Frequent Related Errors
- Confusing copper hydroxide with copper oxide (CuO, black) or copper carbonate (CuCO3, green).
- Ignoring its basic but weakly amphoteric nature when answering acid-base questions.
- Assuming copper hydroxide is easily soluble; it is actually insoluble in water.
- Mixing up color changes (e.g., blue for copper hydroxide, green for copper carbonate).
Uses of Copper Hydroxide in Real Life
Copper hydroxide is widely used as a fungicide in agriculture, helping protect crops from fungal infections. It acts as a colorant and pigment in ceramics. In laboratories, it serves as a standard for analytical chemistry and as a precursor in the production of other copper compounds. It's also used in aquaculture to prevent external infections in fish.
Relevance in Competitive Exams
Students preparing for NEET, JEE, and Olympiads should be familiar with copper hydroxide, as it often features in reaction-based problems, precipitation experiments, salt analysis, and color-change identification. Its reactions are important in both conceptual and numerical chemistry questions.
Relation with Other Chemistry Concepts
Copper hydroxide is closely related to topics such as bases and transition metals, helping students build a bridge between inorganic chemistry, periodic trends, and practical laboratory analysis. It is also relevant when learning about solubility, double displacement reactions, and qualitative cation identification.
Step-by-Step Reaction Example
1. Take dilute copper sulfate solution in a beaker.2. Add sodium hydroxide solution dropwise while stirring.
3. A blue precipitate forms instantly.
4. Write the balanced equation:
CuSO4 (aq) + 2 NaOH (aq) → Cu(OH)2 (s, blue) + Na2SO4 (aq)
5. Discuss color: The blue color confirms presence of Cu2+ ions.
Lab or Experimental Tips
Remember copper hydroxide by its trademark blue gelatinous precipitate and its insolubility in water. Vedantu educators often use this tip in live sessions: "If you see a bright blue solid during a double displacement reaction with copper(II) salts, it's likely copper hydroxide."
Try This Yourself
- Write the IUPAC name of copper hydroxide.
- State whether copper hydroxide shows acidic or basic behavior in water.
- Give two real-life examples of copper hydroxide uses in agriculture or chemistry labs.
Final Wrap-Up
We explored copper hydroxide—its structure, properties, reactions, and real-life importance. For more in-depth explanations and exam-prep tips, explore live classes and expert notes on Vedantu. Revising this topic, especially the reactions and color observations, will help you score well in competitive exams and school tests.
Related study topics: Precipitation Reaction, Transition Metals, Solubility, Copper Sulphate (CuSO4).
FAQs on Copper Hydroxide – Formula, Properties, Preparation, & Uses
1. What is the formula for copper hydroxide?
The chemical formula for copper hydroxide is Cu(OH)₂. This indicates that each molecule contains one copper(II) ion (Cu²⁺) and two hydroxide ions (OH⁻).
2. What color is copper hydroxide?
Copper hydroxide is typically a pale blue-green to light blue solid. The exact shade can vary depending on the preparation method and the presence of impurities.
3. Is Cu(OH)₂ acidic or basic?
Cu(OH)₂ is a weak base. It reacts with acids to form copper salts and water. While it's not highly soluble, the dissolved portion produces hydroxide ions (OH⁻), which increase the pH of the solution.
4. What are the main uses of copper hydroxide?
Copper hydroxide has several applications, including:
- As a fungicide in agriculture.
- As a pigment in paints and ceramics.
- As a reagent in various chemical processes and laboratory experiments.
- In the production of other copper compounds.
5. How is copper hydroxide prepared in the laboratory?
Copper hydroxide can be prepared by adding an alkali solution such as sodium hydroxide (NaOH) to a solution of a soluble copper(II) salt like copper(II) sulfate (CuSO₄). A pale blue-green precipitate of copper hydroxide will form: CuSO₄(aq) + 2NaOH(aq) → Cu(OH)₂(s) + Na₂SO₄(aq)
6. What happens when copper hydroxide is heated?
Heating copper hydroxide causes it to decompose, forming copper(II) oxide (CuO) and water (H₂O): Cu(OH)₂(s) → CuO(s) + H₂O(g). The copper(II) oxide is a black solid.
7. What is the solubility of copper hydroxide in water?
Copper hydroxide has low solubility in water. It is considered an 'insoluble' compound for most practical purposes, meaning only a very small amount dissolves.
8. How does copper hydroxide function as a fungicide?
Copper hydroxide acts as a contact fungicide, meaning it kills fungi upon direct contact. The copper ions interfere with fungal enzyme activity and cell wall formation, preventing growth and reproduction.
9. What is the difference in appearance between copper(I) and copper(II) hydroxides?
Copper(II) hydroxide, Cu(OH)₂, is typically a pale blue-green precipitate. Copper(I) hydroxide, CuOH, is less common and is usually yellow or reddish-brown.
10. What are some common misconceptions about copper hydroxide's base strength?
A common misconception is that because it's a hydroxide, it must be a strong base. While it does have basic properties, it is considered a weak base due to its low solubility and limited dissociation in water.
11. Can copper hydroxide be safely disposed of in water systems?
No, copper hydroxide should not be disposed of in water systems without proper treatment. Copper ions can be toxic to aquatic life at certain concentrations. Follow local regulations for proper disposal of chemical waste.
12. How does the structure of Cu(OH)₂ compare to other transition metal hydroxides?
The structure of Cu(OH)₂ often involves polymeric structures with bridging hydroxide ligands. The specific structure can vary depending on factors like temperature and pH. Comparing it to other transition metal hydroxides requires considering their oxidation states and the coordination geometry around the metal ion, leading to varying degrees of polymerization and solubility.
