Dilution is the process of reducing the concentration of a solute in a solution, usually by adding more solvent (commonly water in laboratory settings). It does not change the total number of moles of solute present; instead, it increases the volume of the solution, thereby lowering the concentration.

For example, if you dissolve 10 g of sodium chloride (NaCl) in 100 mL of water, the solution has a relatively high concentration. If you then add another 100 mL of water, the amount of NaCl remains the same, but the concentration is reduced by half.

The Dilution Equation

The principle of dilution is mathematically expressed as:

\[
C_1 V_1 = C_2 V_2
\]

Where:

• C₁ = initial concentration of the solution
• V₁ = volume of the concentrated solution taken
• C₂ = final concentration of the solution after dilution
• V₂ = final total volume of the solution

This equation works because the number of moles of solute before and after dilution remains constant:

\[
n_1 = n_2
\]

Key Concepts

1. Conservation of Solute – The total solute remains unchanged during dilution; only the solvent volume changes.
2. Units of Concentration – Dilution can be calculated in molarity (mol/L), ppm, ppb, %, or other unit systems, as long as the same unit is used consistently for both C₁ and C₂.
3. Practical Use – Dilutions are commonly performed in chemistry, biology, and medicine for preparing solutions of desired concentrations (e.g., culture media, titration solutions, or drug formulations).

Example Calculation

Suppose you need to prepare 250 mL of a 0.1 M NaOH solution from a 1.0 M stock solution.

Using the dilution equation:

\[
C_1 V_1 = C_2 V_2
\]

\[
(1.0 \, \text{M})(V_1) = (0.1 \, \text{M})(250 \, \text{mL})
\]

\[
V_1 = 25 \, \text{mL}
\]

So, you would measure 25 mL of the 1.0 M NaOH stock solution and dilute it with water until the total volume is 250 mL.

Applications of Dilution

• Laboratory Chemistry – Preparing standard solutions for experiments.
• Pharmaceuticals – Adjusting drug concentrations for safe administration.
• Environmental Science – Measuring pollutant concentrations in water or air samples.
• Food and Beverage Industry – Standardizing flavors, additives, and preservatives.