Problem 6 - 43 Years JEE ADVANCED (1978-2020) + JEE MAIN Chapterwise & Topicwise Solved Papers Chemistry

Question

The number of water molecules(s) not coordinated to copper ion directly in \(\mathrm{CuSO}_{4} \cdot 5 \mathrm{H}_{2} \mathrm{O}\), is: [Main April 9, 2019 (I)] (a) 2 (b) 3 (c) 1 (d) 4

Step-by-Step Solution

Answer

The number of non-coordinated water molecules is 1.

Step 1: Understanding the Compound Composition

The chemical formula of the compound is \(\mathrm{CuSO}_{4} \cdot 5 \mathrm{H}_{2}\mathrm{O}\). This means for every \(\mathrm{CuSO}_4\) unit, there are five water molecules of crystallization.

Step 2: Identifying Coordination with Copper Ion

In the compound \(\mathrm{CuSO}_{4} \cdot 5 \mathrm{H}_{2}\mathrm{O}\), copper (Cu) generally coordinates directly with 4 water molecules and forms a complex. This is due to the fact that copper, being a transition metal, tends to form complexes with two or four water ligands.

Step 3: Determining Non-Coordinated Water Molecules

Since 4 out of the 5 water molecules coordinate with the copper ion, we subtract these 4 coordinated waters from the total water of crystallization: \(5 - 4 = 1\). This 1 remaining water molecule does not coordinate with the copper ion directly.

Key Concepts

Transition Metals

Transition metals are a group of metals found in the central block of the periodic table. They are known for their ability to form various complex compounds due to their unique electronic configuration. Transition metals have partially filled d orbitals, which is key to their special properties.

These metals can:

• Form variable oxidation states. This gives them flexibility in bonding and chemical reactions.
• Act as excellent catalysts in industrial and chemical processes due to their ability to lend and take electrons easily.
• Form coordination complexes by bonding with various ligands, like water in many cases.

One notable characteristic is their tendency to exhibit vibrant colors in compounds. This is because the splitting of d orbitals upon coordination allows them to absorb and emit different wavelengths of light.

Overall, the characteristics of transition metals make them indispensable in both nature and industry, displaying a wide range of chemical behaviors that stem from their d electrons.

Complex Compounds

Complex compounds are formed when transition metals bind to ligands through coordinate covalent bonds. In these compounds, the metal atom or ion acts as a central atom, while the ligands surround it, providing lone pairs of electrons to form bonds.

Some key points regarding complex compounds include:

• The central metal ion can accommodate multiple ligands, forming a coordination sphere.
• The geometry of these complexes can vary. Common arrangements include octahedral, square planar, and tetrahedral.
• Stability of these complexes depends on several factors, such as the nature of the metal and ligands, as well as the metal's oxidation state.

The ligands can be neutral molecules like water, or anions that balance the charge of the complex. These compounds often play crucial roles in biological systems, like hemoglobin in blood, which is a complex of iron with organic ligands.

Complex compounds are central to many key processes and are extensively used in fields like medicine, catalysis, and material science.

Water of Crystallization

Water of crystallization refers to water molecules that are integrated into the crystalline structure of certain compounds. These water molecules can be crucial for maintaining the integrity and form of the crystal but don't necessarily participate in the chemical reactions of the compound.

In compounds like \[ \mathrm{CuSO}_4 \cdot 5 \mathrm{H}_2\mathrm{O} \] (copper sulfate pentahydrate), some of these water molecules may coordinate to the central metal ion, forming a part of a complex. Others might just be trapped in the lattice and are thus not directly involved with metal coordination.

Features of water of crystallization:

• Essential for maintaining the structure of specific crystalline materials.
• Upon heating, these water molecules can be removed, leading to changes in the structure of the compound.
• Not directly participating in chemical bonding but influencing physical properties like melting point and color.

In the case of copper sulfate pentahydrate, there is one water molecule that remains uncoordinated, highlighting that all water of crystallization can influence a compound's characteristics without always directly bonding to the central metal ion.