Solutions are common liquid mixtures where a dissolved substance (the solute) is evenly dispersed throughout a dissolving medium (the solvent). Water is frequently called the universal solvent due to its ability to dissolve many compounds, making it a key component in solutions used in laboratories, industry, and daily life. When the strength of these liquid mixtures needs adjustment, a chemical procedure is often used. This discussion defines and explains the fundamental operation that occurs when more solvent, particularly water, is incorporated into an existing solution.
The Process: Dilution and Concentration
The process of adding more solvent, such as water, to a prepared solution is formally named dilution. Dilution decreases the concentration of the solute within the solution. Concentration refers to the amount of solute present relative to the total solution volume. When water is added, the total volume increases, but the total amount of the dissolved solute remains the same.
This spreads the solute particles over a larger space, lowering the solution’s overall strength. For example, adding water to strongly flavored juice makes the taste less intense because the flavor molecules are less densely packed. The initial, stronger solution is often called the stock solution. Dilution allows for the preparation of a less concentrated, or weaker, working solution from this stock.
Quantifying the Change: The Dilution Equation
Scientists must precisely calculate the resulting strength of a solution after dilution. The standard unit for expressing concentration in chemistry is Molarity (\(M\)), which represents the number of moles of solute per liter of solution. Chemists rely on a simple mathematical relationship known as the dilution equation, \(C_1V_1 = C_2V_2\), to predict the outcome of adding solvent. Here, \(C\) is concentration and \(V\) is volume.
The subscript ‘1’ refers to the initial, more concentrated stock solution, while ‘2’ represents the final, diluted solution. This formula works because the total quantity of solute is conserved throughout the process. Since the number of moles of solute equals concentration multiplied by volume (\(C \times V\)), the equation states that the amount of solute in the initial solution (\(C_1V_1\)) must equal the amount of solute in the final solution (\(C_2V_2\)).
By knowing any three of the four variables, the fourth unknown can be determined, allowing for accurate preparation of the desired final concentration. For instance, if a specific volume of a known stock solution (\(C_1\) and \(V_1\)) is diluted to a new final volume (\(V_2\)), the resulting concentration (\(C_2\)) can be calculated. This mathematical prediction ensures that laboratory experiments and industrial processes use the correct chemical strengths.
Essential Applications of Dilution
The ability to accurately reduce solution concentration is a foundational technique used across many fields.
Medicine and Pharmacy
Highly concentrated stock medications must be diluted to safe and effective concentrations for patient use. These precise dilutions ensure patients receive the correct dosage without administering an overly potent substance.
Manufacturing and Industry
Concentrated cleaning agents or industrial chemicals are often shipped in a strong form to reduce transportation costs and then diluted on-site. This allows the end-user to customize the strength for a particular application.
Laboratory Use
Laboratories rely on dilution to create calibration standards, which are solutions of known concentrations used to standardize instruments and ensure measurement accuracy. Serial dilution, a step-by-step process, is also employed in microbiology to reduce the number of microorganisms in a sample to a countable level.
Safe Methodology for Diluting Solutions
When preparing a diluted solution, especially with concentrated acids or bases, strict safety protocols must be followed. The process of dissolving some solutes, particularly strong acids like sulfuric acid, is highly exothermic, meaning it releases a significant amount of heat. This heat generation can be dangerous if not managed correctly.
The cardinal rule is to always add the concentrated substance slowly to the water, never the reverse. If water is added to concentrated acid, the less dense water remains on top of the heavier acid. The extreme heat generated at the interface can cause the small amount of water to flash-boil, resulting in the corrosive acid splattering out of the container. When the acid is added to a large volume of water, the water effectively absorbs and dissipates the heat as it is generated, preventing dangerous boiling and splashing. For precise work, specialized laboratory glassware, such as a volumetric flask, is used to ensure the final volume is measured accurately.