Plastic volumetric flasks are essential tools in laboratories for accurately preparing solutions of a specific concentration. These flasks have a narrow neck and a wide body, with a plastic lid that fits securely. A calibration mark is engraved on the neck, and when the liquid reaches this line at the specified temperature, it indicates the exact volume stated on the flask. Each volumetric flask is designed for one specific volume only. Common sizes include 25ml, 50ml, 100ml, 250ml, 500ml, 1000ml, and now our company is developing a 2000ml version 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 tight. Fill the flask halfway with water, insert the stopper, and invert it while holding the bottom. Check for any leakage. Rotate the stopper 180° and repeat the test. If no water leaks, the flask is ready for use.
2. **Dissolve the solute**: Weigh the solid solute accurately and dissolve it in a beaker with 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 several times and add the washings to the flask.
3. **Adjust the volume**: Add distilled water until the liquid level is just below the calibration mark. Then use a dropper to carefully bring the meniscus to the exact mark. If you overshoot, discard the solution and start over.
4. **Mix thoroughly**: Close the stopper and invert the flask several times to mix the solution evenly. If the liquid level drops slightly after standing, do not add more water—this is normal and does not affect the concentration.
**Important tips when using plastic volumetric flasks:**
- Each flask is calibrated for a single volume, so choose the correct size based on your needs.
- Only dissolve substances that don’t generate heat directly in the flask. Most solutes should be dissolved in a beaker first.
- Be careful not to exceed the calibration mark when washing the beaker.
- Do not heat the flask, as temperature changes can affect accuracy.
- Volumetric flasks are for preparation only, not storage. Some solutions may damage the plastic or affect the calibration.
- Clean and sterilize the flask as needed to maintain its integrity and accuracy.
By following these guidelines, you can ensure precise and reliable results in your laboratory work.
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