1. Introduction
When we talk about acids and bases in daily life or in the laboratory, we often hear the words “concentrated” and “dilute”. These terms tell us how much of an acid or base is present in a solution, not how strong it is.
Understanding concentration and dilution helps us handle acids and bases safely and use them correctly for experiments.
2. What is Concentration?
The concentration of an acid or base shows how much of the acid/base (solute) is present in a given amount of water (solvent).
When there is more acid or base dissolved in less water, the solution is called concentrated.
2.1. Concentrated Solution
A concentrated solution contains a large amount of acid or base dissolved in a small amount of water.
For example: Thick, syrup-like hydrochloric acid in a lab bottle is a concentrated solution.
2.2. Dilute Solution
A dilute solution contains a small amount of acid or base dissolved in a large amount of water.
Example: Lemon juice mixed with a lot of water becomes a dilute solution of citric acid.
2.3. Visual Comparison
- More solute + Less water = Concentrated
- Less solute + More water = Dilute
3. How Dilution Works
Dilution simply means adding more water to a solution. When water is added:
- The number of acid/base particles stays the same.
- But they spread out in more water.
- So, the solution becomes less harmful and less reactive.
This is very important for safety because concentrated acids and bases can be dangerous.
3.1. Important Rule of Dilution
When diluting a strong acid:
Always add acid to water, never water to acid.
This prevents splashing and overheating.
3.2. Why Adding Water Weakens the Effect
As water is added, the ions become more spread out, so the solution becomes less reactive. But remember: dilution does not change the strength of the acid or base itself.
4. Difference Between Strength and Concentration
Students often confuse these two terms, so here is a clear difference:
- Strength = how completely an acid or base ionises in water.
- Concentration = how much acid or base is mixed in a given amount of water.
So:
- A strong acid can be dilute (if mixed with a lot of water).
- A weak acid can be concentrated (if very little water is added).
4.1. Examples
- Strong but dilute acid: A small amount of HCl in a bucket of water.
- Weak but concentrated acid: A thick solution of acetic acid (vinegar acid) with very little water.
5. Measuring Concentration
Concentration is often measured in terms of:
- Percentage (%) of solute in solution
- Molarity (M): moles of solute per litre of solution
- Normality (N): gram equivalents per litre
For school-level understanding, knowing the idea of concentrated vs dilute is enough.
6. Why Concentration and Dilution Matter
The concentration of acids and bases is important in:
- Chemical reactions — concentrated solutions react faster and more vigorously.
- Safety — concentrated acids and bases can burn skin and materials.
- Industry — different processes require precise concentrations.
- Cooking — lemon water becomes less sour when diluted.