Problem 23 - A Complete Resource Book in Chemistry for JEE Main

Question

The solution of sugar in water contains (a) free ions (b) free atoms (c) free molecules (d) free atoms and molecules

Step-by-Step Solution

Answer

The solution contains free molecules (c).

Step 1: Understand the components of the solution

When sugar dissolves in water, it dissociates into its individual molecules, but not into ions or atoms. Water, a polar solvent, helps to disperse these sugar molecules throughout the solution.

Step 2: Analyze the nature of sugar molecules

Sugar is a covalent compound, and when it dissolves in water, it doesn't break into ions as ionic compounds do. Instead, the sugar stays as molecules.

Step 3: Determine the type of particles present in the solution

Since sugar remains as molecules and does not dissociate into ions or atoms, the correct answer should involve free molecules present in the solution.

Key Concepts

Understanding Polar Solvents

When we talk about polar solvents, we're referring to liquids like water that have a positive and negative pole. These poles are a result of the way water molecules are shaped and the electric charges of their atoms.

Here's how it works:

• Water molecules have a bent shape with two hydrogen atoms at one end and an oxygen atom at the other.
• The oxygen atom is more electronegative, meaning it tends to pull shared electrons closer, creating a slight negative charge on that side of the molecule.
• The hydrogen atoms end up with a slight positive charge.

This separation of charges leads to the polar nature of water, making it an excellent solvent for other polar substances or ionic compounds. When sugar dissolves in water, the partially charged areas of water molecules interact with the sugar molecules, helping to break them apart and disperse them throughout the solution.

Covalent Compounds Explained

Covalent compounds, like sugar, are made up of molecules in which atoms share electrons. This sharing occurs because the atoms involved have similar electronegativities. Let's simplify what this means:

• Sugar is a covalent compound, which means it is not made up of ions like table salt is but of molecules that are bound together through shared electrons.
• The bonds within sugar molecules are strong, so when sugar is dissolved in water, these bonds remain intact.
• The sugar molecules do not break into ions or individual atoms; they remain whole molecules.

Because covalent bonds within sugar remain unbroken, when sugar dissolves in water, it doesn't dissociate. Instead, water breaks up the clumps of sugar molecules, distributing these molecules throughout the solvent.

Molecular Solutions and Their Properties

A molecular solution is a type of solution where the solute is dissolved as molecules, not ions or atoms. This is what happens when sugar dissolves in water.

• In a molecular solution such as sugar water, the solute (sugar) dissolves at the molecular level without forming ions.
• These molecular solutions are typically non-conductive because there are no charged particles, like ions, to carry an electric current.
• Instead, the sugar molecules remain intact, simply dispersed throughout the water.

Understanding this helps us realize why sugar in water is a solution of free molecules, not free ions or atoms. It's a perfect example of how a covalent compound forms a molecular solution in a polar solvent like water.