Problem 18 - A Complete Resource Book in Chemistry for JEE Main

Question

A saturated solution of non-radioactive sugar was taken and a little radioactive sugar was added to it. A small amount of it gets dissolved in solution and an equal amount of sugar was precipitated. This proves (a) the equilibrium has been established in the solution (b) radioactive sugar can displace non-radioactive sugar from its solution. (c) Equilibrium is dynamic in nature (d) none of the above

Step-by-Step Solution

Answer

(c) Equilibrium is dynamic in nature.

Step 1: Understanding Equilibrium in Solutions

A saturated solution means the solution has the maximum amount of solute dissolved into the solvent at a given temperature. Adding more solute typically does not dissolve in the solution.

Step 2: Analyze the Added Radioactive Sugar

When a small amount of radioactive sugar is added, some of it dissolves while an equal amount of non-radioactive sugar precipitates out. This suggests that the solution is at a point of equilibrium.

Step 3: Exploring the Implication of Sugar Dissolution

In this context, the dynamic nature of equilibrium in solutions means the dissolved sugar and the precipitated sugar are continuously exchanged between being in solution and out of solution.

Step 4: Conclusion from the Solution Behavior

Since radioactivity helps to trace the sugar movement, it becomes evident that radioactivity does not displace non-radioactive sugar but rather they continuously interchange at equilibrium.

Key Concepts

Dynamic Equilibrium

In chemistry, dynamic equilibrium refers to a state where the rate of the forward reaction equals the rate of the reverse reaction. It is a balance that is reached when both processes occur at the same rate, resulting in no net change over time.
For instance, when radioactive sugar is added to a saturated non-radioactive sugar solution, both types of sugar molecules continuously interchange between dissolving into the solution and precipitating out. Therefore, although individual molecules move in and out of solution, the overall concentration remains constant.
This concept reveals that even in a static-looking saturated solution, there is constant activity at the molecular level. The dissolved and undissolved sugars don't just sit; they continue to move in and out of the solution, maintaining a dynamic equilibrium.

Saturated Solution

A saturated solution is one where, at a given temperature, the maximum amount of solute has been dissolved in the solvent. Adding more solute will not increase the concentration of the solution, as it will not dissolve any further.
In our exercise, the solution is saturated with non-radioactive sugar, meaning it has dissolved as much sugar as possible at that temperature. When radioactive sugar is introduced, some of it dissolves, leading to the precipitation of an equivalent amount of non-radioactive sugar.
This saturation and the resulting behavior highlight how saturated solutions exist precisely at the threshold where equilibrium can occur. This is a perfect demonstration of how dynamic equilibrium operates in a saturated solution.

Radioactive Tracing

Radioactive tracing is a technique involving the use of radioactive isotopes to trace the path and exchange of chemical substances. It exploits the unique ability of radioactive isotopes to emit detectable radiation.
In the exercise, adding radioactive sugar helps understand how sugar molecules dynamically shift between being part of the dissolved solute and precipitated solid. The radioactive component allows scientists to track the exact pathway and mutation of molecules between phases.
With radioactive tracing, the movement of sugar molecules in and out of the solution becomes evident. This method provides an insightful way to visualize and comprehend the dynamic processes happening in chemical equilibrium, serving as a powerful tool in scientific studies involving equilibrium.