A dilution is the process of reducing the concentration of a solute in a solution, usually by mixing it with more solvent. This process is fundamental across many scientific disciplines, including chemistry, biology, and medicine, as well as in practical applications like preparing household cleaners. The 1:100 ratio is a frequently used standard for achieving a substantial, yet precise, reduction in the strength of an initial stock solution. Understanding this ratio allows for accurate preparation of reagents and samples, ensuring consistency in experimental results or product efficacy.
Interpreting the 1:100 Ratio
The notation 1:100 signifies a volume-to-volume dilution, expressing the relationship between the concentrated substance and the final solution volume. The “1” represents one part of the original, concentrated stock substance (the solute). The “100” refers to the total number of parts that will make up the final, diluted solution, establishing the exact factor of concentration reduction.
Preparing a 1:100 dilution means taking one unit of the concentrated material and adding enough solvent to bring the total volume to 100 units. For example, one milliliter (mL) of stock solution is combined with exactly 99 mL of solvent to reach a final volume of 100 mL. This is a total volume ratio, meaning the 100 represents the final volume, not the volume of added solvent.
Calculating Volumes for a Target Solution
The mathematical planning for a 1:100 dilution relies on the principle that the final volume is 100 times the volume of the concentrated stock solution. To calculate the necessary volume of the concentrated solute (\(V_{solute}\)), divide the desired final volume (\(V_{final}\)) by 100: \(V_{solute} = V_{final} / 100\). The volume of solvent needed (\(V_{solvent}\)) is found by subtracting the solute volume from the total volume: \(V_{solvent} = V_{final} – V_{solute}\).
For example, if the target volume is 100 mL, the required stock solution is 1 mL (\(100 \text{ mL} / 100\)). This 1 mL of stock is mixed with 99 mL of solvent. Scaling up is straightforward: if the target volume is 500 mL, 5 mL of concentrated stock is needed, combined with 495 mL of diluent to achieve the \(500 \text{ mL}\) final volume.
For large-scale preparation, such as 1 Liter (1000 mL), 10 mL of the stock solution must be used. The remaining 990 mL of solvent is required to reach the total volume. Accurate pre-calculation is paramount, ensuring the diluted solution has the exact intended concentration for its specific application.
The Physical Dilution Procedure
Once volumes are calculated, the physical preparation begins, prioritizing precision and safety. Appropriate equipment must be selected based on required accuracy; for laboratory work, a volumetric pipette measures the solute, and a volumetric flask holds the final volume. For less critical applications, graduated cylinders may suffice for both components.
First, accurately dispense the calculated volume of the concentrated stock solution into the designated final vessel. It is recommended to add approximately half to two-thirds of the total required solvent volume to the flask before adding the concentrated solute. This initial layer of solvent minimizes the risk of the solute adhering to the glass surface and promotes immediate dispersion.
After the solute is introduced, gently mix the solution by swirling or carefully inverting the flask. Excessive agitation should be avoided, especially with protein-based solutions, as this can lead to undesirable foaming. The remaining solvent is then added carefully until the liquid level approaches the calibration mark (meniscus) on the neck of the volumetric flask.
The final, high-precision step is “bringing to volume” by adding the last few drops of solvent until the bottom of the meniscus precisely aligns with the etched calibration line. The flask must then be sealed with a stopper and inverted multiple times—typically five to ten times—to guarantee the entire solution is homogenous and the target concentration is uniform throughout.