Volumetric flasks are primarily used to accurately formulate solutions of a certain concentration. It is a slender neck, pear-shaped flat-bottomed glass bottle with a ground plug. The bottleneck is engraved with a marking. When the liquid in the bottle reaches the marking line at the specified temperature, its volume is the number of volumes indicated on the bottle.
Glass-Volumetric-Flask
The method of using a volumetric flask to prepare a solution is:
1. Check for leaks at the cork before use (new purchase after cleaning). The specific operation method is: put half a bottle of water in the volumetric flask, plug the stopper, use the right index finger to hold the stopper, and the other hand holds the bottom of the volume bottle, put it upside down (the bottle mouth is facing down), observe the capacity. Is the bottle leaking? If there is no water leakage, set the bottle upright and rotate the stopper 180°, then stand upside down again to check whether there is water leakage. If it is operated twice, the bottle around the volume bottle will not leak out, indicating that the volume bottle does not leak. A volumetric bottle that has been checked for leaks can be used.
2. Place the accurately weighed solid solute in a beaker and dissolve it with a small amount of solvent. The solution is then transferred to a volumetric flask. In order to ensure that all the solute can be transferred to the volumetric flask, the beaker is washed several times with the solvent, and the washing solution is completely transferred to the volumetric flask.
Use a glass rod to drain when transferring. The method is to place one end of the glass rod against the inner wall of the capacity bottleneck, taking care not to let other parts of the glass rod touch the volume bottle mouth to prevent liquid from flowing to the outer wall of the volumetric bottle. After adding an appropriate amount of solvent, shake it for initial mixing.
3. When the liquid level added to the volumetric flask is about 0.5~1 cm, it should be carefully added with a dropper. Finally, the meniscus of the liquid is exactly tangent to the marking. If the water is added above the tick, it will need to be reconstituted.
4. Close the stopper and mix the liquid in the bottle evenly by inverting and shaking. If the liquid level is lower than the tick mark after standing, this is because a very small amount of solution in the volumetric flask is lost at the bottleneck, so it does not affect the concentration of the prepared solution, so do not add water to the bottle, otherwise, it will make The concentration of the formulated solution is lowered.
5. Open the lid and return: After mixing, carefully open the volume cap, let the solution at the cap and the bottle mouth flow back into the bottle, cover the cap, and then mix the liquid in the bottle by inverting and shaking.
This is very important when dealing with small volume samples. The following points should be noted when using a volumetric flask:
1.After the volume bottle is purchased, it must be cleaned and calibrated. Only after the calibration is passed can it be used.
2. The substance that is easy to dissolve and does not generate heat can be directly dissolved into the volumetric flask. Other substances can’t dissolve the solute in the volumetric flask. The solute should be dissolved in the beaker and transferred to the volumetric flask.
3. For water and organic solvents (such as methanol), it will be exothermic, endothermic or volume change solution should be noted, for the heat to add appropriate amount of solvent (about 0.5 cm from the bottle line), let cool to Re-constant to the mark at room temperature; add appropriate amount of solvent for the change of volume (do not add to the neck to facilitate shaking), shake, and then add to the distance of about 0.5 cm from the bottle line, after a period of time Make up to the scale.
4. The total amount of solvent used to wash the beaker must not exceed the marking line of the volumetric flask.
5. The volumetric flask cannot be heated. If the solute releases heat during the dissolution process, the solution should be cooled after the solution is cooled, because the general volumetric flask is calibrated at a temperature of 20 ° C. If a higher or lower temperature solution is injected into the volumetric flask, the volumetric flask is Will expand and contract, the volume will be inaccurate, resulting in inaccurate concentration of the solution.
6, the volume bottle can only be used to prepare the solution, and can not store the solution for a long time, because the solution may corrode the bottle (especially alkaline solution) so that the accuracy of the volumetric bottle is affected.
If you have any questions, please feel free to communicate with laboratory glassware manufacturer WUBOLAB
