Problem 49 - A Complete Resource Book in Chemistry for JEE Main

Question

The white anhydrous copper sulphate decomposes to give (a) \(\mathrm{CuO}+\mathrm{SO}_{3}\) (b) \(\mathrm{Cu}\) (c) \(\mathrm{CuSO}_{4} \cdot \mathrm{H}_{2} \mathrm{O}\) (d) \(\mathrm{CuSO}_{4} \cdot 5 \mathrm{H}_{2} \mathrm{O}\)

Step-by-Step Solution

Answer

The correct answer is (a) \( \mathrm{CuO} + \mathrm{SO}_3 \).

Step 1: Understand the Chemical Compound

Anhydrous copper sulphate is the chemical compound with the formula \( \mathrm{CuSO}_4 \). It involves copper, sulfur, and oxygen without any water molecules attached.

Step 2: Understand "Decomposition"

When a compound decomposes, it breaks down into simpler substances. We need to determine the products of the decomposition of \( \mathrm{CuSO}_4 \).

Step 3: Identify Typical Decomposition Products

Anhydrous copper sulphate \( \mathrm{CuSO}_4 \) typically decomposes into copper(II) oxide \( \mathrm{CuO} \) and sulfur trioxide \( \mathrm{SO}_3 \) when heated, releasing the sulfur trioxide into the atmosphere.

Step 4: Match the Correct Option

Since the decomposition product is copper(II) oxide and sulfur trioxide, which matches option (a) in the given list: \( \mathrm{CuO} + \mathrm{SO}_3 \).

Key Concepts

Anhydrous Copper Sulphate

Anhydrous copper sulphate is a chemical compound represented by the formula \( \mathrm{CuSO}_4 \). This means it is composed of copper (Cu), sulfur (S), and oxygen (O) atoms. The term "anhydrous" signifies that the compound does not contain any water molecules.
This is an important distinction, as copper sulphate can also exist in hydrated forms where it is bound with water molecules, like in the case of the well-known blue copper sulphate pentahydrate \( \mathrm{CuSO}_4 \cdot 5 \mathrm{H}_2 \mathrm{O} \).
In its anhydrous form, copper sulphate appears as a white powder. It is often used in dry environments or when it needs to absorb moisture due to its hygroscopic nature.

• Formula: \( \mathrm{CuSO}_4 \)
• Color: White
• Molecular Weight: 159.61 g/mol

Understanding the characteristics and uses of anhydrous copper sulphate is crucial before studying its decomposition reaction.

Chemical Compound

Chemical compounds are substances formed by the combination of two or more elements in a fixed ratio. These compounds have properties distinct from their individual component elements. A compound contains molecules, which are groups of two or more atoms bonded together by chemical bonds. When we talk about a chemical compound like anhydrous copper sulphate \( \mathrm{CuSO}_4 \), we refer to how these atoms are specifically bonded together.
Compounds can be classified into various types depending on their composition, such as:

• Inorganic compounds: typically formed from metals and non-metals, like \( \mathrm{CuSO}_4 \)
• Organic compounds: primarily carbon-based compounds

The properties of a compound, such as solubility, reactivity, and color, depend heavily on the type and arrangement of the atoms within its molecules. These properties can predict the behavior of the compound under various conditions, aiding in understanding reactions like decomposition.

Copper(II) Oxide

Copper(II) oxide, also known as cupric oxide, is a chemical compound consisting of copper and oxygen with the formula \( \mathrm{CuO} \). It is a black solid and is one of the products formed when anhydrous copper sulphate \( \mathrm{CuSO}_4 \) undergoes decomposition.
The decomposition reaction of anhydrous copper sulphate is an example of how heat can cause a chemical compound to break down into simpler substances. Copper(II) oxide, being a basic oxide, has its own set of chemical properties:

• Appearance: Black solid
• Solubility: Insoluble in water
• Reactivity: Reacts with acids to form copper salts

Understanding copper(II) oxide is important in many fields, including metallurgy, where it is used for ore smelting and as a pigment. Its formation through decomposition demonstrates a key principle of chemistry: the transformation and reformation of elements into various compounds during chemical reactions.