Calibration of glass measuring instruments in food physical and chemical testing (2)

4.

When it is necessary to use chromic acid lotion to clean the measuring device, it should be noted that the chromic acid lotion is highly corrosive, which will burn the skin and damage the clothing.

5.

(1) The calibration of the burette Put distilled water into the cleaned burette, adjust the liquid level to the zero mark or slightly below the zero mark, and record the reading and record the temperature of the water

Add distilled water to adjust the liquid level to the zero mark or slightly below the zero mark, and record the reading

Note: When discharging water, touch the tip of the burette to the wall of the conical flask to prevent water droplets from splashing

(2) Calibrating the pipette Take a clean pipette to be calibrated, draw water to the mark, and record the temperature of the water

(3) Calibrating the volumetric flask Dry the washed volumetric flask and weigh it accurately, and then inject distilled water to the scale (there is no drop of water above the mark on the inner wall of the bottleneck, otherwise it will affect the calibration result), and record the water temperature

6.

(1) Refer to Table 1-5, Table 1-6 and Table 1-7 for data records

Table 1-5 Burette calibration record table

Table 1-6 Pipette calibration record table

Table 1-7 Volumetric flask calibration record table

(2) Calculation formula

In the formula △ _V ——correction value, mL

V _T ——Volume of released water, mL

V ₂₀ ——actual volume, mL

7.

(1) When calibrating volumetric instruments, you must strictly abide by their rules of use

(2) When calibrating the measuring instrument with the weighing method, the measuring instrument and the calibration water should be put into the working room at least 4 hours in advance to ensure that the room temperature, water temperature and measuring instrument temperature are basically the same, so as to avoid large measurement errors
.

(3) In the calibration of the glass measuring instrument, the cleanliness of the inner wall of the measuring instrument is very important
.

If the inner wall of the measuring instrument is not clean, it will produce a deformed meniscus, and may also cause the instability of the meniscus shape, which directly affects the correct observation and measurement of the liquid level
.
For burettes and pipettes, dirty inner walls can also cause "water hanging" and measurement errors
.

(4) The electronic balance can weigh up to 0.
0001g, but during calibration, the mass of the conical flask and water only needs to be recorded to the milligram level
.

(5) In different teaching materials and standards, the operation steps of burette segmentation correction are different
.

(6) In actual work, each point should be calibrated twice in parallel, and then averaged
.

Related Links: Calibration of Glass Measuring Instruments in Food Physical and Chemical Testing (1)