When water is added to a solution, its concentration decreases. This fundamental principle of chemistry, known as dilution, is a direct consequence of altering the ratio of solute to solvent.
The Science Behind Dilution
As stated in the reference, "When additional water is added to an aqueous solution, the concentration of that solution decreases. This is because the number of moles of the solute does not change, but the total volume of the solution increases."
Let's break down why this happens:
- Constant Solute: The amount (number of moles) of the dissolved substance (solute) remains the same. Adding water does not create or remove the solute; it merely adds more solvent to the existing solute.
- Increased Volume: Water acts as a solvent. By adding more water, you increase the total volume of the solution.
- Concentration Formula: Concentration is typically defined as the amount of solute per unit volume of solution (e.g., moles per liter for molarity, or mass per volume). Since the amount of solute stays constant while the total volume increases, the solute becomes "spread out" over a larger volume, leading to a lower concentration.
Key Factors in Concentration Change
Understanding the variables involved helps clarify the process:
- Solute Moles (n): Remains constant during dilution.
- Solution Volume (V): Increases when water is added.
- Concentration (C): Decreases as a result of the increased volume.
This relationship can be seen in the general concentration formula:
Concentration = Amount of Solute / Volume of Solution
| Factor | Before Water Added | After Water Added |
|---|---|---|
| Solute Moles | Constant | Constant |
| Solution Volume | Lower | Higher |
| Concentration | Higher | Lower |
Practical Implications & Examples
Dilution is a common process with many real-world applications:
- Making Drinks Less Sweet: If you find a juice too sweet, adding water dilutes it, making it less concentrated in sugar and therefore less sweet to taste.
- Laboratory Dilutions: Chemists frequently dilute concentrated stock solutions to prepare less concentrated working solutions for experiments. This is crucial for safety and accuracy. For instance, a concentrated acid must often be diluted before use.
- Household Cleaning Products: Many concentrated cleaning agents are designed to be diluted with water before use to achieve the effective and safe concentration for cleaning.
- Medication Preparation: In some cases, liquid medications might need to be diluted to achieve the precise dosage required, especially for pediatric patients.
Understanding Molarity
While concentration can be expressed in various ways (e.g., percent by mass, parts per million), molarity (moles of solute per liter of solution) is one of the most common units. When water is added, the number of moles of solute remains the same, but the total volume of the solution increases, directly leading to a decrease in molarity.
