Using Volumetric Flasks
Materials: ★★☆ Available in most school laboratories or specialist stores
Difficulty: ★★☆ Can be done by science teachers
Safety: ★☆☆ Minimal safety procedures required
Categories: Chemical Quantities and Calculations, Lab Skills and Safety
Alternative titles: Preparing Dilutions with Volumetric Flasks
Summary
Volumetric flasks are precision glassware designed for preparing exact solution volumes, most often used for making dilutions and standard solutions. They allow accurate adjustment of a liquid to a single graduation mark, ensuring reliable concentrations for laboratory testing.
Procedure
Calculate the required volume of stock solution needed.
(stock volume × stock concentration = final volume × final concentration).
Pipet the calculated volume of stock solution into a clean volumetric flask.
Fill with distilled or lab-grade water until the liquid level is just below the graduation line.
Stopper and mix thoroughly, then allow to return to room temperature if needed.
Using a dropper, carefully add water until the bottom of the meniscus rests on the line.
Mix again and transfer the final solution to a labeled storage container.
Links
Variations
Prepare serial dilutions (10×, 100×, 1000×) by successively diluting a previous solution.
Use different flask sizes (25 mL to 1000 mL) depending on the volume of solution required.
Substitute plastic volumetric flasks with caps for fieldwork where breakage is a risk.
Safety Precautions
Use lab-grade water appropriate to the test (e.g., ammonia-free water for nitrogen tests).
Ensure volumetric flasks are clean and dry before use to avoid contamination.
Handle glass flasks carefully to avoid breakage and cuts.
Label all prepared solutions clearly to prevent mix-ups.
Questions to Consider
Why do volumetric flasks have only one graduation line? (To ensure maximum accuracy at a single calibrated volume.)
What is the difference between a stock solution and a standard solution? (Stock solution is concentrated; standard solution is the diluted form prepared for testing.)
How does serial dilution differ from volumetric dilution? (Serial dilution uses stepwise dilutions, often by factors of 10; volumetric dilution prepares a single target concentration directly.)
What errors might occur if the meniscus is not read at eye level? (Parallax error leads to inaccurate volume measurement.)