Plastic volumetric flasks are essential laboratory tools used to prepare solutions of precise molarity. These flasks have a narrow neck and a round body, with a plastic lid that seals the opening. A calibrated mark on the neck indicates the exact volume at a specific temperature. When the liquid reaches this mark, the volume inside is exactly as stated on the flask. Each volumetric flask is designed for one specific volume only. Common sizes include 25ml, 50ml, 100ml, 250ml, 500ml, and 1000ml. Our company is now focusing on developing 2000ml plastic volumetric flasks to meet growing demands.
To prepare a solution using a plastic volumetric flask, follow these steps:
1. **Check for leaks**: Before use, ensure the stopper is airtight. Fill the flask halfway with water, insert the stopper, and invert it. Check for any leakage. If no water drips out, rotate the stopper 180 degrees and repeat the test. If no leakage occurs, the flask is ready for use.
2. **Dissolve the solute**: Accurately weigh the solid solute and dissolve it in a beaker using a small amount of solvent. Transfer the solution to the volumetric flask using a glass rod to guide the flow, ensuring all the solute is transferred. Rinse the beaker with more solvent and add it to the flask.
3. **Adjust the volume**: Add solvent gradually until the liquid level is just below the calibration mark. Then, use a dropper to carefully bring the liquid up to the exact mark, making sure the bottom of the meniscus touches the line. If you go over, start over.
4. **Mix the solution**: Close the stopper and shake the flask thoroughly by inverting it several times. If the level drops slightly after standing, do not add more water, as this would dilute the solution.
**Important considerations when using plastic volumetric flasks:**
- Each flask is designed for one specific volume only. Always choose the correct size based on your needs.
- Only substances that dissolve easily without generating heat can be dissolved directly in the flask. Others should be dissolved in a beaker first.
- Be careful not to exceed the calibration mark when washing the beaker.
- Never heat the flask, as it can cause expansion or contraction, leading to inaccurate measurements.
- Volumetric flasks are for preparation only, not storage. Some solutions may corrode the plastic or affect accuracy.
- Clean and sterilize the flask regularly to maintain its performance and longevity.
By following these guidelines, you can ensure accurate and reliable results when preparing solutions in the lab.
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