Problem 14 - A Complete Resource Book in Chemistry for JEE Main

Question

Which of the following solution would exhibit abnormal colligative properties? (a) \(1 \mathrm{M}\) glucose (b) \(0.1 \mathrm{M} \mathrm{NaCl}\) (c) \(0.1 \mathrm{M}\) sucrose (d) 10 gram glass powder in water

Step-by-Step Solution

Answer

Glass powder in water exhibits abnormal colligative properties.

Step 1: Understanding Colligative Properties

Colligative properties depend on the number of solute particles in a solution, not their identity. These include properties like boiling point elevation, freezing point depression, osmotic pressure, and vapor pressure lowering.

Step 2: Identifying Normal Solutes

From the choices, glucose, NaCl, and sucrose are common solutes that typically dissolve to form solutions with predictable colligative properties. Glucose and sucrose are non-electrolytes, while NaCl is an electrolyte that dissociates into ions.

Step 3: Evaluating Each Choice

(a) A 1 M glucose solution is expected to show normal colligative properties for a non-electrolyte. (b) A 0.1 M NaCl solution will dissociate into Na⁺ and Cl⁻ ions, exhibiting normal colligative properties for an electrolyte. (c) A 0.1 M sucrose solution will behave typically for a non-electrolyte. (d) Glass powder does not dissolve in water; it forms a suspension, not a solution, and does not affect colligative properties.

Step 4: Conclusion

Since glass powder does not dissolve and does not alter colligative properties in water, it represents an abnormal case as it cannot exhibit colligative properties in the way solutions do.

Key Concepts

Non-electrolytes

Non-electrolytes are substances that dissolve in a solvent without dissociating into ions. They usually form solutions that do not conduct electricity. Common examples include organic molecules like glucose and sucrose. When non-electrolytes like these dissolve in water, the resulting solution exhibits predictable colligative properties. This happens because the solute particles do not split into smaller charged entities.

• Non-electrolytes do not change the ionic strength of the solution.
• They have a straightforward effect on colligative properties because the number of particles remains constant.
• In solutions of non-electrolytes, properties such as boiling point elevation and freezing point depression depend solely on the concentration of the solute.

Hence, when you make a solution with glucose or sucrose, you can expect it to follow normal colligative behavior due to its nature as a non-electrolyte.

Electrolytes

Electrolytes, in contrast to non-electrolytes, are compounds that dissociate into ions when dissolved in water. This dissociation into positive and negative ions enables the solution to conduct electricity. A familiar example of an electrolyte is sodium chloride (NaCl), which dissociates into Na⁺ and Cl⁻ ions in solution.

• Electrolytes increase the ionic strength of the solution, affecting properties like electrical conductivity.
• In electrolytic solutions, colligative properties are affected by the number of ions formed.
• A solution containing an electrolyte like NaCl will exhibit colligative properties based on the total number of ions in the solution, increasing effects like boiling point elevation and osmotic pressure.

It's important to note that electrolytic solutions can show more pronounced colligative properties due to the presence of multiple particles from dissociation.

Suspensions

Suspensions are mixtures where fine particles are dispersed throughout a liquid but do not dissolve. An example from our exercise is glass powder in water. Unlike true solutions, the particles in a suspension are large enough to be seen with the naked eye and are not affected by colligative properties.

• Suspensions do not involve solute particles interacting on a molecular level with the solvent.
• They do not alter boiling point, freezing point, or osmotic pressure because the particles don't dissolve.
• Upon standing, particles in a suspension tend to settle out due to gravity, distinguishing them from colloids or solutions.

Thus, since suspensions like glass powder in water don't form homogeneous mixtures, they do not conform to the typical behaviors associated with colligative properties.