[China Glass Network] It is an indispensable skill for every analyst to be able to use glass instruments correctly. Because glass has high chemical stability and thermal stability, it involves the use of various glass instruments in experimental analysis. The chemical stability of the glass is good, but it is not immune to erosion, but the degree of erosion is in accordance with certain standards. The analysis of ions in the adsorption solution due to the erosion of glass and trace ions into the solution on the surface of the glass is a problem to be paid attention to in the microanalysis; hydrofluoric acid strongly corrodes the glass, so it cannot be used to contain hydrogen fluoride. The acid test; the glass instrument for storing the lye can not open the ground if the grinding device is stuck together, so the glass container cannot store the lye for a long time. . .
So, what are the details of using a glass instrument?
First, the mistakes in the washing of glass instruments
1. The cleaning of glass instruments is a step forward in the inspection work. In practice, many people often neglect to clean the glassware used immediately before and after the inspection, or to clean the appliance. As a result, the inner wall of the appliance is heavily hung with water droplets, dirt, and precipitated dry matter adhered to the inner wall, etc., which cannot be cleaned, directly affecting the accuracy of the data.
2. There are many varieties and items in general quality inspection. It is impossible to use a set of special instruments for each indicator. It is often used alternately, and the instruments used are not strictly cleaned or cleaned. It will inevitably cause alternating contamination between reagents. Thereby affecting the accuracy of the test results.
3. On the other hand, the capacity measuring tool is mixed with the non-capacity measuring tool property and the washing method, and both are washed with the decontamination powder, which causes the capacity of the measuring device to be inaccurate and affects the accuracy of the measurement result.
Second, the error in the heating of the glass container
1. The heating process is a common step in physical and chemical analysis. In actual work, some people often ignore or simply can't figure out which instruments can be heated, and even make mistakes. In fact, glass containers are not directly heated, such as measuring cylinders, measuring cups, volumetric flasks, reagent bottles, etc. can not be directly heated. Reaction vessels such as beakers, flasks, and flasks should be used as appropriate. If the basic knowledge is not known in the actual work, there will be errors and even inspection accidents.
2. When heating the glass container, the container is not placed on the asbestos net, but the container is placed directly in the electric furnace, so that the container is unevenly heated or even bursts.
3. During use, the temperature changes too much, or the hot glass container that is quenched or removed at high temperature is placed directly on the table, and is not placed on the asbestos net as required, causing the container to rupture and the reagents to be lost, which may affect the normal operation of the inspection. .
4. In actual work, some people are afraid of trouble and are not accustomed to using the dryer properly. For the heating device that needs accurate weighing, it should be dried and taken out slightly cold (about 30s), put into a desiccator and cooled to room temperature for weighing ( 30min can be). When the warm appliance is placed in the dryer, leave a gap in the cover and wait a few minutes to cover it tightly; when moving the dryer, you should not only lower the lower part, but hold the cover to prevent the cover from slipping, causing no The necessary loss.
Third, the mistakes in the selection and use of glass containers
Accurate measurement of the volume of a solution in a volumetric analysis is an important factor in obtaining good analytical results. Therefore, it is necessary to correctly use the volumetric instruments, such as burettes, pipettes, volumetric flasks, etc., and there are often some errors in actual operation.
1. The acid burette and the basic burette cannot be correctly distinguished and their properties. The acid burette is often mistaken for the basic burette during use; the basic burette is mistaken for the acid burette. This is a mistake. Because the acid burette has a glass piston at the lower end, it cannot hold an alkaline solution because the alkaline solution can corrode the glass. Rotate the piston. The bottom of the basic burette is connected with a rubber tube, and can not contain a solution of corrosion rubber such as acid or oxidant, such as AgNO3, KM-nO4, I2 and the like.
Before the burette is filled into the standard solution, the burette is washed 2 to 3 times without first using the standard solution 5 mL to 10 mL. During operation, the two-handed flat-end burette is slowly rotated to allow the standard solution to flow through the entire tube, and the solution is allowed to flow out from the lower end of the burette to remove residual water in the tube. Refill the solution for titration, otherwise the standard solution concentration will be diluted.
Do not use different types of burettes correctly according to the amount of standard solution for titration. Generally, the dosage is below 10mL. Use 10mL or 5mL micro-burette. The dosage is between 10mL and 20mL. Use 25mL burette. If the dosage exceeds 25mL, use 50mL burette. In actual work, some people do not pay attention to this error. Some standard solutions use less than 10mL still use 50mL burette, some standard solution more than 25mL still use 25mL burette, divided into several times, etc., these cases are wrong practices, causing large errors.
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