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Chapter 13: Problem 92

A saturated solution of sucrose \(\left(\mathrm{C}_{12} \mathrm{H}_{22} \mathrm{O}_{11}\right)\) is made by dissolving excess table sugar in a flask of water. There are \(50 \mathrm{~g}\) of undissolved sucrose crystals at the bottom of the flask in contact with the saturated solution. The flask is stoppered and set aside. A year later a single large crystal of mass \(50 \mathrm{~g}\) is at the bottom of the flask. Explain how this experiment provides evidence for a dynamic equilibrium between the saturated solution and the undissolved solute.

Short Answer

Expert verified
The experiment with sucrose crystals provides evidence for a dynamic equilibrium between the saturated solution and the undissolved solute. This is because the mass of the undissolved sucrose stays constant over time, even though the crystals dissolved and re-precipitated. This observation indicates that the rates of dissolution and precipitation of sucrose in the solution are happening at equal rates, maintaining a constant solute concentration in the solution, which is consistent with a dynamic equilibrium.

Step by step solution

01

Understand Dynamic Equilibrium

Dynamic equilibrium is a state where the rate of a forward process (e.g., dissolution of a solute in a solvent) exactly equals the rate of the reverse process (e.g., precipitation of the solute from the solution). In other words, the concentrations of the reacting species remain constant over time, but microscopic processes continue to happen at a molecular level.
02

Initial State of the Solution

Initially, the solution is saturated with undissolved sucrose crystals weighing \(50 \mathrm{~g}\). This situation indicates that the process of sucrose dissolving into water is occurring at the same rate as the process of sucrose precipitating out of the solution; this leads to a constant concentration of dissolved sucrose, and hence we have a dynamic equilibrium established right from the beginning of the experiment.
03

Changes Observed After a Year

After a year, it is observed that a single large crystal of mass \(50 \mathrm{~g}\) is at the bottom of the flask. This transformation suggests that the smaller undissolved sucrose crystals have dissolved and then re-precipitated over time, combining to form a single large crystal.
04

Relate Observed Changes to Dynamic Equilibrium

The fact that the mass of the undissolved sucrose remains constant after a year (\(50 \mathrm{~g}\)) indicates that the concentration of sucrose in the solution stayed the same throughout the entire period. This observation is consistent with the dynamic equilibrium, where the rates of dissolution and precipitation of sucrose in the solution remain constant.
05

Conclusion

The experiment provides evidence for a dynamic equilibrium between the saturated solution of sucrose and the undissolved solute because, although the physical state of the solute undergoes a change (small crystals to a single larger crystal), the mass of undissolved sucrose remains the same over time. This consistency supports the idea that dissolution and precipitation processes are occurring at equal rates, maintaining a constant solute concentration in the solution.

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Most popular questions from this chapter

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