A solution, a homogeneous mixture, forms when one substance disperses evenly into another, making it uniform in composition. The substance being dissolved is the solute, and the substance doing the dissolving is the solvent. Solutions are widely used in home cleaning, medicine preparation, and scientific research. Accurately preparing a solution with a specific concentration is a fundamental skill in many applications. This guide will provide clear instructions on how to calculate and physically prepare a solution at a 5% concentration.
Defining Percentage Solutions
The term “percentage solution” refers to the amount of solute present relative to the total amount of the final solution. A 5% solution means that 5 parts of the solute are contained within 100 total parts of the final mixture. Understanding this ratio is the basis for all concentration calculations.
Percentage solutions are primarily defined by the state of matter of the solute and the solvent. The two most common types are weight/volume (w/v) and volume/volume (v/v). A weight/volume solution involves dissolving a solid solute, measured by mass, into a liquid solvent, with the final solution measured by volume. For example, a 5% w/v solution contains 5 grams of solute dissolved in a final volume of 100 milliliters of solution.
Conversely, a volume/volume solution is created when a liquid solute is mixed with a liquid solvent. A 5% v/v solution requires 5 milliliters of the liquid solute to be present in a total volume of 100 milliliters of the final solution. Identifying whether the solute is a solid or a liquid is the necessary first step before any arithmetic is performed.
Calculating the Required Measurements
The arithmetic for preparing a 5% solution is based on the principle of proportion. The amount of solute needed is 5% of the desired total volume of the solution. This calculation can be simplified using the formula: Amount of Solute = Desired Final Volume × 0.05.
If the goal is to make a 5% w/v solution, the amount of solute must be measured in grams and the final volume in milliliters. For instance, creating 500 mL of a 5% w/v solution requires multiplying the target volume (500 mL) by 0.05, which yields 25 grams of solute. This means 25 grams of the solid must be dissolved to reach a total volume of 500 mL.
For a 5% v/v solution, both the solute and the final volume are measured using the same volume units, typically milliliters. To prepare a 2,000 mL batch of a 5% v/v solution, the calculation involves multiplying 2,000 mL by 0.05, which equals 100 mL of the liquid solute. This calculated amount of solute is then brought to the 2,000 mL final volume using the solvent.
Practical Steps for Solution Preparation
Preparing the solution requires precise measuring tools and adherence to procedure. Equipment includes an accurate scale for weighing solid solutes, a graduated cylinder for measuring liquid volumes, and a stir rod or magnetic stirrer for ensuring the components are fully mixed.
When working with a solid solute (w/v), the calculated mass of the solid must first be accurately weighed out. The solid is then transferred into a container, and a volume of solvent that is less than the final total volume is added to facilitate dissolution. It is recommended to fill the container about two-thirds full to start, allowing the solute to dissolve completely before proceeding.
After the solute is fully dissolved, the final step is to add the remaining solvent until the mixture reaches the predetermined final volume mark. This process, known as “bringing to volume,” is necessary because the added solute itself occupies space and affects the final volume.
For liquid solutes (v/v), the measured amount of liquid solute is simply mixed with the solvent, bringing the total volume to the calculated final measurement.
The mixture must be made homogeneous by thoroughly mixing the solution after the final volume has been reached. For laboratory glassware with stoppers, this involves securely closing the container and inverting it a number of times to ensure uniform concentration throughout the entire batch.
Handling and Storage Protocols
Once the 5% solution is prepared, proper handling and storage are necessary. Every container must be immediately and clearly labeled with the name of the contents, the concentration (5%), and the date of preparation. This labeling prevents confusion and misuse, especially if multiple solutions are stored in the same area.
Solutions should be kept in tightly closed containers to prevent evaporation of the solvent, which would inadvertently increase the concentration over time. Storage should be in a cool, dark, and dry area, away from direct sunlight or heat sources that could degrade the components. Observing a “first-in, first-out” system helps ensure the freshest stock is used.
General safety during handling involves wearing appropriate personal protective equipment, such as gloves and eye protection, especially if the solute or solvent is known to be irritating. Solutions should be stored in designated areas, segregated by hazard type, and never above eye level to prevent spills and accidents. Regularly inspecting the stored solutions for any signs of deterioration or container damage is important.