Which piece of glassware would be best to choose to accurately deliver 20.00 ml of solution?
The correct answer and explanation is:
Correct Answer: A 20.00 mL volumetric pipette
Explanation (300 words):
When precision and accuracy are essential in delivering a fixed volume of liquid, volumetric pipettes are the gold standard in laboratory glassware. Specifically, a 20.00 mL volumetric pipette is designed to deliver exactly 20.00 mL of liquid with high accuracy and very low uncertainty (often ±0.03 mL or better, depending on calibration and class).
Volumetric pipettes are calibrated to deliver (TD) a specific volume at a particular temperature (usually 20°C). They have a single graduation mark, which helps minimize user error. Unlike graduated cylinders or beakers, which offer flexibility at the expense of precision, volumetric pipettes are ideal when accuracy is more important than versatility.
Here’s how other common glassware compares:
- Graduated cylinder: Designed to measure a range of volumes, but the markings are not as precise. A 25 mL graduated cylinder may have an error margin of ±0.5 mL or more.
- Beaker: Intended primarily for mixing, heating, or holding liquids—not for precise volume measurement. Its error is even higher, often ±5% of the volume.
- Burette: Highly accurate for titration, as it allows you to deliver variable volumes and read to the nearest 0.01 mL. However, it’s not ideal if you need to deliver exactly 20.00 mL in one go, unless it’s part of a titration process.
- Measuring flask (volumetric flask): Designed for preparing a fixed volume, not delivering it.
Therefore, if your task is to deliver exactly 20.00 mL of a solution, especially in quantitative analysis or titration, the 20.00 mL volumetric pipette is the best choice due to its precision, narrow error margin, and purpose-specific design.