Correct use of the hottest glass gauge

2022-08-15
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Correct use of glass gauge

1) general principle

when the highest accuracy is required, the parts should be carefully selected according to the calibration time as far as possible, and the calibration value of graduation error is required. The gauge should be cleaned before use. If there is any deviation in the indicated capacity during calibration, appropriate correction should be made

2) volumetric flask

if a volumetric flask is used to prepare an aqueous solution, it is not necessary to dry it after cleaning with distilled water. The recommended method of diluting the aqueous solution is as follows: add an appropriate amount of water to the dissolved substances to be dissolved in the processing and manufacturing of key components such as super large and super long pull rods, and heat them appropriately and shake them to dissolve them when necessary. Then add water to make the liquid level rise to a few centimeters below the scale line. After mixing with the cork, rinse with the bottle washing water to make the liquid level rise to 1cm below the scale line, open the volumetric flask cork and let it stand for 2 minutes to drain the liquid in the bottleneck. To make the solution reach room temperature again, you can cover the cork and wait for a certain time. Finally, flow a certain amount of water along the bottleneck from a point within 1cm below the scale line, so that the lowest point of the meniscus is set on the scale line. Close the cork and shake the volumetric flask upside down to make the solution even and stand by

3) measuring cylinder and measuring cup

after cleaning and drying, fill the measuring cylinder with the liquid to be measured to a few millimeters above the nominal capacity mark or the required mark, and then suck out the excess liquid with a straw

4) buret

after the buret (including plug valve and liquid outlet) is cleaned with distilled water, it is rinsed three times with the test solution to be used. If the buret size is not large enough, and the thermometer cannot be inserted into its top to observe the liquid temperature, an ordinary glass test tube sufficient to hold the thermometer can be set and clamped next to the buret

fill the burette clamped in the vertical position with water to a few millimeters above the zero line. If the pipe wall is wet, there should be sufficient drainage time before setting the zero line. In order to eliminate bubbles between the plug valve and the flow port, discharge some liquid from the flow port before setting the zero line

outflow time refers to the time taken for the liquid to flow freely from the zero line to the nominal capacity when the plug valve is fully opened. In order to obtain the best accuracy, the division correction value should be used. When discharging liquid, the plug valve should be fully opened, and the liquid outlet should not be in contact with the receiving container and liquid level. Therefore, for the buret, it is best to estimate how many milliliters of solution the sample needs to consume to reach the end point. If there are enough samples, a pre titration can be carried out to get this point. If this cannot be done, as long as the titration time does not exceed the specified outflow time of 60s, the error generated is generally less than ± TM l when the capacity tolerance is ± TML. If the waiting time is specified, it is the time after the plug valve is closed and before the final reading. Generally, it is not allowed to observe the waiting time when the titration is in progress, because the time to reach the titration end point is generally longer than the specified waiting time

the above use cases are applicable to transparent liquids with viscosity similar to that of water. Especially viscous liquids cannot be used accurately and conveniently, because a large amount of mucus will be left on the pipe wall and the flow rate is very slow, but the diluted aqueous solution usually used for volumetric analysis is applicable and has no obvious error. For example, 1 mol/the weight and size will change as a result of wear, and the error caused by L solution is less than the tolerance of class A. And 0. The error of 1mol/l solution is correspondingly smaller. When non-aqueous liquids are used, the accuracy will also be reduced because their surface tension is very different from that of water. For the liquid with poor visibility at the bottom of the meniscus, it can be read at the upper edge of the meniscus, but the accuracy is worse than that observed at the lowest point of the meniscus

5) measuring pipette

after cleaning the pipette with distilled water, rinse it with the liquid to be used. The pipette sucks the liquid to a few millimeters above the zero mark or the required scale line. It is recommended to use a suction device that can make the liquid to be measured flow freely, such as a suction ball

in order to obtain the correct measuring capacity, the pipette should be operated according to the method described in the relevant capacity definition in its product standard. Before the pipette separates from the receiving container, the specified waiting time shall be observed when the test piece is subjected to axial pressure. Generally, 3S is enough for the waiting time of the pipette wall hanging liquid to flow to the liquid outlet, and accurate measurement is not required. Once it is determined that the meniscus reaches the flow port and tends to be stationary, the pipette can be out of contact with the receiving container. The residual liquid left at the liquid outlet shall not be discharged, and the "blow out" pipette shall blow out its last residual liquid as part of the measuring capacity. Like burette, very viscous liquid cannot be easily and accurately absorbed. The diluted aqueous solution usually used for volumetric analysis is applicable, and there is no obvious error

6) measuring pipette

dry it after cleaning with distilled water or rinse it with the solution to be tested three times. Suck the liquid above the zero mark or the required scale line. In order to obtain the correct measuring capacity, the pipette should be operated according to the method described in the relevant capacity definition

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