Tennessee Wastewater Operator Practice Exam

What is the correct procedure for emptying a volumetric pipette?

1. Invert the pipette and shake it

2. Touch the tip to the wet surface of the receiving vessel after outflow stops

3. Completely invert the pipette for thorough drainage

4. Let it drain without touching the receiving vessel

The correct answer is: Touch the tip to the wet surface of the receiving vessel after outflow stops

The correct procedure for emptying a volumetric pipette involves allowing the liquid to drain out and then touching the tip of the pipette to the wet surface of the receiving vessel after the outflow has stopped. This practice helps ensure that any liquid that remains in the tip is transferred to the receiving vessel, which is essential for accurate measurements in volumetric analysis. Touching the tip to the receiving vessel allows for the last drop of liquid in the pipette to be dispensed into the receiving container. This step is crucial because volumetric pipettes are designed to deliver a specific volume, and any liquid that stays in the tip can lead to inaccuracies in the final volume delivered. Other methods, such as shaking the pipette or completely inverting it, are not standard practice because they may not ensure the entire volume is accurately delivered and could lead to unintended spillage or measurement errors. Additionally, allowing the pipette to drain without touching the receiving vessel may result in some of the liquid remaining in the tip, which again affects the precision of the dispensed volume. By following the correct procedure, accuracy and reliability in measurements are upheld, which is vital in laboratory settings.