Views: 35 Author: Site Editor Publish Time: 2020-10-12 Origin: Site
1. Calculation: the mass of the solid or the volume of the liquid.
2. Weighing: Pay attention to the accuracy of the balance when weighing solids, and also pay attention to the accuracy of the measuring cylinder and burette when measuring liquid dao. For example, the tray balance cannot weigh out 5.85 g of solid NaCl, and the graduated cylinder cannot output the volume of 5.25 mL of liquid. Because their accuracy is 0.1. It is recommended to use an electronic balance.
3. Dissolution: It is usually carried out in a beaker. During the dissolution process, there is a thermal effect, so it needs to be cooled. This is because the capacity and specification of the volumetric flask are limited by temperature. If it is not cooled, it will be produced due to thermal expansion. error.
4. Liquid transfer: When transferring liquid, use a glass rod for drainage, and its lower end should generally be placed below the scale line on the inner wall of the volumetric flask.
5. Washing: Wash the beaker and glass rod with distilled water 2 to 3 times, the purpose is to transfer the solute to the volumetric flask as much as possible to prevent errors.
6. Constant volume: When adding water to the volumetric flask to the mark of 1 cm～2 cm, then use a plastic dropper to the mark.
7. Shake well: If the liquid level is below the graduation mark at this time, do not add water.
8. Bottling: The volumetric flask cannot hold the liquid for a long time. It should be placed in the designated reagent bottle and labeled.
Precautions:
1. Only the solution with the specified volume on the volumetric flask can be prepared.
2. The glass rod should be placed below the scale line when transferring the solution.
3. If the fixed volume with water exceeds the scale line, the excess cannot be sucked away, but should be re-constituted.
4. When using a plastic dropper to make the volume constant, the eyes should look at the liquid level.
5. If the liquid level is lower than the scale line after shaking, no more water can be added.
