When an equilibrium is established between dissolved and undissolved solutes, the solution is said to be?

Step 1: Analyze the question The question asks what we call a solution in which dissolved and undissolved solute are in equilibrium with each other.

Step 2: Explain the concept

• Unsaturated solution: can still dissolve more solute at that temperature. No undissolved solute remains, so there is no equilibrium with solid.
• Saturated solution: holds the maximum amount of solute possible at a given temperature. Extra solute stays undissolved, and a dynamic equilibrium exists: the rate of dissolving equals the rate of crystallizing.
• Concentrated / Dilute: these describe the relative amount of solute (a lot or a little). They say nothing about equilibrium. A solution can be dilute and saturated if the solute is only slightly soluble, such as PbCl₂.

Step 3: Apply it Equilibrium between dissolved and undissolved solute:

solute (undissolved) ⇌ solute (dissolved)

The rate of dissolution equals the rate of crystallization, so no more solute can dissolve at that temperature. That is the definition of a saturated solution.

Step 4: Answer Saturated**.

Exam tip: Whenever you see "equilibrium" with "undissolved solute" or "maximum solute at a given temperature", think saturated. Remember that "concentrated" and "dilute" describe only how much solute is present, not whether the solution is saturated.