How to use volumetric flask correctly

The measuring flask is mainly used to accurately prepare a certain concentration of solution.It is a long neck, pear-shaped flat bottom glass bottle with a grinding stopper.The bottleneck is marked, and when the liquid in the bottle reaches the mark at the specified temperature, its volume is the number of volumes indicated on the bottle.
The method of preparing solution using volumetric flask is as follows:
1. Check if the bottle stopper leaks before use (check after purchasing and cleaning).The specific operation method is: fill a half bottle of water in the volumetric flask, plug the stopper tightly, hold the stopper with the right index finger, and hold the bottom of the volumetric flask with the other five fingers, turn it upside down (the bottle mouth is facing down), and observe whether the volumetric flask leaks.If there is no water leakage, put the bottle upright and rotate the stopper 180 degrees, then turn it upside down again to check whether there is water leakage. If there is no water leakage around the stopper of the volumetric bottle after two operations, that is to say, the volumetric bottle does not leak.The water-tight volumetric flask can only be used after inspection.
2. Place the accurately weighed solid solute in the 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 solutes can be transferred to the volumetric flask, the beaker should be washed with solvent for many times, and the washing solution should be transferred to the volumetric flask.Glass rod drainage should be used when transferring.The method is to lean one end of the glass rod on the inner wall of the capacity bottleneck, and pay attention not to let other parts of the glass rod touch the capacity bottle mouth to prevent liquid from flowing to the outer wall of the capacity bottle.After adding appropriate amount of solvent, shake and mix.
3. When the liquid level added to the volumetric flask is about 0.5-1 cm off the mark line, the dropper should be used instead to drip carefully, and finally the meniscus of the liquid should be exactly tangent to the mark line.If the water addition exceeds the scale line, it needs to be reconstituted.
4. Close the stopper and mix the liquid in the bottle evenly by inversion and shaking.If the liquid level is found to be below the scale line after standing, this is because a very small amount of solution in the volumetric flask is lost by wetting at the bottleneck, so it does not affect the concentration of the prepared solution, so do not add water to the flask, otherwise, the concentration of the prepared solution will be reduced.
5. Open the cap and reflux: after mixing, carefully open the cap of the volumetric bottle, let the solution at the cap and the bottle mouth flow back into the bottle, then cover the cap, and then use the method of inversion and shaking to make the liquid in the bottle mix evenly.This is important when handling small volumes of samples.
The following points should be noted when using volumetric flasks:
1. Volumetric bottles should be cleaned and calibrated after purchasing, and used only after calibration is qualified.
2. Soluble and non-heating substances can be dissolved directly in the volumetric flask. Other substances can not be dissolved in the volumetric flask basically. Solubles should be dissolved in the beaker and transferred to the volumetric flask.
3. For the solution which will exothermic, endothermic or volume change after mixing water with organic solvent (such as methanol, etc.), pay attention to adding appropriate amount of solvent (about 0.5 cm away from the mark of the bottle) for heating, cooling it to room temperature and then setting the volume to the scale; for volume change, add appropriate amount of solvent (do not add to the fine neck to facilitate shaking), shaking, and then adding it to the distance from the bottle to the mark.The line is about 0.5 cm away, and the volume is fixed to the scale after a period of time.
4. The total amount of solvent used to wash the beaker should not exceed the mark of the volumetric flask.
5. Volumetric flask cannot be heated.If the solute is exothermic in the dissolution process, it should be transferred after the solution is cooled, because the general volumetric flask is calibrated at the temperature of 20 C. If the solution with higher or lower temperature is injected into the volumetric flask, the volumetric flask will expand and shrink, and the volume will be inaccurate, resulting in inaccurate concentration of the prepared solution.
6. Volumetric flasks can only be used to prepare solutions and cannot store solutions for a long time, because solutions may corrode the bottle body (especially alkaline solutions), thus affecting the accuracy of volumetric flasks.
7. The volumetric flask should be washed and cleaned in time after use.

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