Burettes, volumetric flasks, and pipettes commonly used in laboratories are generally calibrated and marked, and can be used directly in general experiments. Correction is required when higher accuracy is required. The general correction method is introduced below, but it is not a precise correction method.
1. Measurement method
The measurement method is to weigh the weight of pure water contained in a certain capacity instrument, record the water temperature, and find out the density of water at this temperature, then the volume can be converted.
First of all, we need to know the relationship between the weight of matter in vacuum and in air:
The weight of a substance in a vacuum can be obtained from the above formula.
In addition, it should be considered that the weighing is carried out at room temperature, so the influence of the volume expansion of the glass container on the weighing should be considered. Dao usually finds the volume of the container at any temperature, and then calculates the exact volume of the container at 20°C by the following formula.
2. Capacity comparison method
In experiments with less stringent requirements, the capacity comparison method can be used for correction. That is to choose a calibrated capacity instrument and use it as a standard to calibrate other containers. For example, with a 25mL pipette that has been calibrated, when calibrating a 100mL volumetric flask, you can pipette 4 times of distilled water into the volumetric flask, and then check whether the liquid level is consistent with the original scale line, if not, you can mark a new scale line . General containers have a certain allowable error, see Table ll-3.
