Question

You are given a bottle of solid \(X\) and three aqueous solutions of \(X \rightarrow\) one saturated, one unsaturated, and one supersaturated. How would you determine which solution is which?

Short answer

Add solid X to each solution; the saturated will not dissolve more, the unsaturated will dissolve more, and the supersaturated will crystallize or precipitate.

Step-by-step solution

- Add More Solid X

Take a small amount of the solid X and add it to each of the three solutions. Observe what happens to the solid X in each solution.

- Identify the Saturated Solution

If the solid X settles at the bottom of the solution and no more dissolves, the solution is saturated. A saturated solution cannot dissolve any additional solid at the given temperature.

- Identify the Unsaturated Solution

If the solid X completely dissolves, the solution is unsaturated. An unsaturated solution has the capacity to dissolve more of the solid X.

- Identify the Supersaturated Solution

If the solid X causes the solution to crystallize or some of the dissolved solid starts to precipitate out immediately upon adding the solid X, the solution is supersaturated. A supersaturated solution contains more dissolved solid than it would under normal circumstances.

Key concepts

saturated solution

A saturated solution is one in which the maximum amount of solute has been dissolved in the solvent at a given temperature. Any additional solid added will not dissolve and will settle at the bottom.
For example, think of trying to dissolve salt in water. If you keep adding salt and stir, at some point, you'll notice that no more salt dissolves; it just sits at the bottom. At this point, the solution is saturated.

Identifying a saturated solution involves adding a small amount of solid to the solution and observing what happens:

• If the solid remains undissolved and settles at the bottom, the solution is saturated.

unsaturated solution

An unsaturated solution is one that contains less solute than the solvent can dissolve at a given temperature. In other words, it has the capacity to dissolve more solute.
Imagine you have a cup of tea and you add a teaspoon of sugar. If the sugar dissolves without any left at the bottom, your tea is an unsaturated solution.

To identify an unsaturated solution, add a small amount of the solute to the solution:

• If the solute completely dissolves, the solution is unsaturated.

supersaturated solution

A supersaturated solution is an unstable condition where the solution contains more dissolved solute than it would normally hold at a given temperature. This occurs when a solution is prepared at a higher temperature and then slowly cooled.
For example, making rock candy involves creating a supersaturated sugar solution by dissolving sugar in boiling water and letting it cool slowly. As it cools, the excess sugar starts to crystallize.

To identify a supersaturated solution, add a small amount of solid solute:

• If crystals begin to form or the solute precipitates out immediately, the solution is supersaturated.

solid dissolution

Solid dissolution is the process of a solid solute dissolving into a solvent to form a homogeneous mixture, or solution. This process involves breaking the intermolecular forces in the solute and solvent, allowing the molecules to interact and mix.
For instance, when salt dissolves in water, the salt crystals break apart into sodium and chloride ions, which then disperse evenly throughout the water.

Factors affecting dissolution include:

• Temperature: Higher temperatures usually increase the rate at which solids dissolve.
• Agitation: Stirring or shaking helps distribute solute particles more evenly.
• Surface Area: Finely ground solids dissolve faster than large chunks due to increased exposed surface area.