Mistakes to Avoid During Operation of Glass Instruments

Various products made of glass are widely used in people's daily life, industrial and agricultural production, and scientific research. From the home window glass, glass, light bulb to the observation window of the spacecraft, it is inseparable from the glass. Glass instruments made using the excellent properties of glass are widely used in various laboratories, such as chemical laboratories, medical test laboratories, biological laboratories, scientific research laboratories, and teaching laboratories. Many companies and laboratories often use glass instruments because of mistakes in their operation, resulting in the damage of glass instruments and inaccurate measurement results. Then, what errors should be avoided during the operation of glass instruments?

Glass instruments should avoid the following mistakes during operation:

(1) Mistakes concerning the basic operation of glass instruments.

(1) When the standard solution is loaded in the burette, the concentration of the standard solution is changed or contaminated by means of a funnel or other container. Before each measurement, the liquid level was not adjusted to the “0.00” position. After the titration was started and ended, the solution adhered to the inner wall was allowed to flow after 1 minute to 2 minutes, and the volume error was immediately caused by the reading. When the titration speed is too fast, the solution will be discharged into a stream. Even close to the end point, the titration speed will not slow down, which will cause the titration over the end point to cause inspection error. When reading (colorless or light-colored solution) does not keep the eye line of sight and the lowest point of the concave surface of the solution in the buret; the colored solution does not make the line of sight of the eye level with the highest point on both sides of the solution surface in the buret. Causes volume error.

(2) When the solution was first drawn with a pipette, it was not necessary to use a filter paper to suck the water inside and outside the tip first, and then the pipette was used to wash the pipette 2 or 3 times to ensure movement. The solution concentration of the solution does not change. When removing the solution, apply the right thumb and middle finger to hold the top of the neck line, and insert the pipette into the solution. Don't be too deep or too shallow. Too deep will make the solution stick too much to the outside of the tube, affecting the amount of solution Accuracy of volume; too shallow tends to produce suction. When putting the solution into place, make the pipe vertical dust against the inner wall of the container, so that the solution in the pipe naturally flows down the entire wall. After waiting for 10s to 15s, remove the pipette and do not blow out the remaining solution. When correcting the pipette, the volume of the solution that has been retained at the end has been considered, otherwise it will cause a volume error and affect the accuracy of the result.

(3) When the reagent is contained, the nature, use, and precautions of the reagent bottle are not known. Feel free to hold, do not follow the solid reagents to hold wide mouth bottles, liquid reagents contained fine bottles, glass plugs for acidic materials, rubber plugs for alkaline materials, see the principle of brown bottles of easily decomposable substances (such as AgNO3, I2 liquid, etc.). This causes errors or changes in the amount of formula. When reagents are used, the stoppers are not placed on the operator's table in accordance with the regulations, resulting in contamination of the reagents and affecting the measurement results.

(4) When using a weighing bottle to weigh the sample, do not dry the weighing bottle first at 105°C and take it after cooling and constant weight; dry the weighing bottle directly by hand instead of using dry and clean The paper strips are set on the weighing bottle. Causes the weighing bottle to be contaminated and affects the accuracy of weighing results.

(b) Mistakes in the washing of glass instruments. (1) The cleaning of glass instruments is the first step in inspection work. In practical work, many people often neglect to clean the glassware used immediately before and after the inspection, or to perform cleaning inspections on the equipment. As a result, water droplets, dirt, and precipitates adhered to the inner wall of the device are severely attached to the inner wall of the device and cannot be cleaned. This directly affects the accuracy of the data. (2) There are many kinds of general quality inspections and items are miscellaneous. It is not possible to use a set of special instruments for each index to be measured. They are often used interchangeably, and the instruments used are not subjected to strict cleaning or cleanliness tests. Inevitably cause alternating contamination between reagents. This will affect the accuracy of the test results. (3) On the other hand, the use of decontaminating powder scrubbing is used for mixing capacity gauges with non-volume gauge properties and washing methods. This results in inaccurate capacity of the capacity gauges and affects the accuracy of the measurement results.

(c) Mistakes in the heating of glass instruments. (1) The heating process is a common step in physicochemical analysis. In the actual work, some people often ignore or simply do not know which instruments can heat, and even make mistakes. In fact, not all glass instruments can be directly heated, such as measuring cylinders, measuring cups, flasks, reagent bottles, etc., which cannot be directly heated. Beakers, flasks, flasks, and other reaction vessels should be used as appropriate. If these basic knowledge are not understood in practical work, mistakes will inevitably occur and even cause inspection accidents. (2) When the glassware is heated, the container is not placed on the asbestos net and the container is placed directly in the electric furnace so that the container is not evenly heated and even bursts. (3) During use, the temperature change is too violent, or the hot glass device quenched or taken off at high temperature is placed on the tabletop directly, but not placed on the asbestos net according to the regulations, causing the container to rupture and the reagents to be lost, affecting the normal inspection work. get on. (4) In actual work, some people are afraid of trouble and are not accustomed to using the dryer properly. For heating devices that need to be accurately weighed, they should be baked and removed and cooled (about 30 seconds), and placed in a desiccator to cool to room temperature for weighing. (30min can be). When the warm appliance is put into the dryer, leave a gap in the lid, wait a few minutes and cover it tightly. When moving the dryer, it should not only end the lower part, but should move it by holding the lid to prevent the lid from falling. Necessary loss.

(4) Mistakes in the selection and use of glass instruments. Accurately measuring the volume of a solution in volumetric analysis is an important factor in obtaining good analytical results. Therefore, it is necessary to correctly use capacity instruments such as burettes, pipettes, volumetric flasks, etc. There are often mistakes in actual operation.

(1) Periodically correct volumetric flasks, burettes, pipettes, etc., as required. Sometimes the nominal value does not correspond to the real volume, causing a volume error and causing systematic errors. It is usually calibrated every six months.

(2) Unfamiliar with the capacity tolerances and standard capacity levels of various gauges. Different types of capacity tolerances are different, resulting in errors caused by the gauge itself due to improper gauge selection. Usually require accurate measurement of a certain volume of solution, the use of pipettes and pipettes, and can not use cylinders, measuring cups and other measuring tools and cause errors.

(3) Acid burettes and alkaline burettes and their properties cannot be correctly distinguished. The acid burette is often mistaken for a basic burette during use; the basic burette is mistaken for an acid burette. This is a mistake. Because the acid burette has a glass piston at its lower end, it cannot hold an alkaline solution because the alkaline solution can erode the glass. Turn the piston. The bottom of the basic burette is connected to a rubber tube, which cannot contain solutions of corrosion rubber such as acid or oxidant, such as AgNO3, KM-nO4, I2, etc. Before the burette is loaded into the standard solution, the buret is not washed with the standard solution 5 mL to 10 mL for 2 to 3 times. During the operation, the two flat-bottom burettes are slowly rotated so that the standard solution flows through the entire tube and the solution flows out from the bottom of the buret to remove residual water in the tube. Then add the solution for titration, otherwise it will cause dilution of the standard solution concentration. Do not use different types of burettes correctly, based on the amount of standard solution used in the titration. The general dosage is below 10mL. Use 10mL or 5mL microtiter tubes. The dosage is between 10mL and 20mL. Use 25mL burette. If the dosage exceeds 25mL, select 50mL burette. In practice, some people do not pay attention to this error. Some standard solutions with less than 10mL still use 50mL burette, and some standard solutions with more than 25mL still use 25mL burette, add several times, etc., these situations are wrong practices, causing greater errors.

(4) Proper use of volumetric flasks not in accordance with the rules. A volumetric flask is a type of volumetric device commonly used to measure the volume of a given solution. This is primarily used for volumetric devices that dilute a certain volume of solution to a certain volume. However, in practice, it is often used for long-term storage of solutions, especially alkaline solutions, which will erode the wall of the bottle and cause the stopper to stick and fail to open. Prepared solution can not be stored in the volumetric flask, but should be promptly poured into the reagent bottle to save, the reagent bottle should be washed with a good solution first 2 to 3 times.