2.4.6 Concentrated and Dilute Solution

This topic explains how solutions are described based on the relative amount of solute they contain. The two terms used are dilute and concentrated.

Definition

Dilute Solution

Dilute solutions are those which contain a relatively small amount of dissolved solute in the solution.

Simple explanation: A dilute solution has only a little solute dissolved in it.

Concentrated Solution

Concentrated solutions are those which contain a relatively large amount of dissolved solute in the solution.

Simple explanation: A concentrated solution has a lot of solute dissolved in it.

Main Idea

These terms describe the concentration of the solution — how much solute is present compared to the solvent.

• Dilute = small amount of solute
• Concentrated = large amount of solute

Important: These are relative terms. They compare solutions to each other, not to a fixed standard.

Core Concept

The book gives one clear example:

Brine is a concentrated solution of common salt in water.

Simple explanation: Brine (very salty water) has a lot of salt dissolved in it, so it is concentrated. If you added more water to it, it would become less concentrated.

Effect of Adding Solvent

Addition of more solvent will dilute the solution and its concentration decreases.

Simple explanation: If you add water to a concentrated solution, it becomes more dilute. The amount of solute stays the same, but there is more solvent, so the concentration goes down.

Detailed Explanation

Concentration — The Key Idea

Concentration refers to how much solute is dissolved in a given amount of solvent or solution.

• High concentration → concentrated solution
• Low concentration → dilute solution

Examples

Adding Solvent vs Adding Solute

• Add more solvent → solution becomes more dilute (concentration decreases).
• Add more solute → solution becomes more concentrated (concentration increases).

Intermediate Level

Dilute vs Concentrated

Important: Dilute/Concentrated vs Saturated/Unsaturated

These are different pairs of terms:

• Dilute and unsaturated — little solute, can still dissolve more.
• Concentrated and unsaturated — lots of solute, but can still dissolve a bit more.
• Concentrated and saturated — lots of solute, no more can dissolve at that temperature.

So "concentrated" does not mean "saturated." A concentrated solution can still be unsaturated.

Important Points

• - Dilute solution: relatively small amount of dissolved solute.
• - Concentrated solution: relatively large amount of dissolved solute.
• - These terms describe the concentration of the solution.
• - Brine is a concentrated solution of common salt in water.
• - Adding more solvent dilutes the solution (concentration decreases).
• - Adding more solute makes it more concentrated (concentration increases).
• - Dilute/concentrated is different from unsaturated/saturated.

Remember

• - Dilute = small amount of solute.
• - Concentrated = large amount of solute.
• - Brine = concentrated salt solution.
• - Adding solvent → more dilute.
• - Adding solute → more concentrated.
• - Dilute/concentrated ≠ unsaturated/saturated.

Common Mistakes

• 1. Thinking dilute = unsaturated. A dilute solution can be saturated if the solute is only slightly soluble.
• 2. Thinking concentrated = saturated. A concentrated solution can still be unsaturated if more solute can dissolve.
• 3. Confusing "concentration" with "amount of solute." Concentration depends on both solute and solvent amounts.
• 4. Thinking adding solvent changes the amount of solute. It doesn't — adding solvent only increases the volume and lowers concentration.
• 5. Treating dilute/concentrated as absolute terms. They are relative — a solution is dilute or concentrated compared to another.

Quick Revision

• Dilute solution: relatively small amount of solute.
• Concentrated solution: relatively large amount of solute.
• These terms describe concentration.
• Brine = concentrated solution of common salt in water.
• Adding solvent dilutes the solution (concentration decreases).
• Adding solute concentrates the solution (concentration increases).
• These terms are relative — they compare one solution with another.
• They are different from unsaturated/saturated.

60-Second Revision

• Dilute = little solute.
• Concentrated = lots of solute.
• Brine = concentrated salt solution.
• Adding solvent → more dilute.
• Adding solute → more concentrated.
• Warning: dilute ≠ unsaturated; concentrated ≠ saturated.