First, the mistakes in the washing of glass glassware
1. Cleaning of glassware is the first step 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 combination of the capacity measuring tool and the non-capacity measuring tool property and the washing method are all 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 overlook 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. cannot 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 volumetric devices, 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 acid or oxidant such as AgNO3, KM-nO4, I2 or 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 a 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 solutions more than 25mL still use 25mL burette, divided into several times, etc., these cases are wrong practices, causing large errors.
2. Do not use the volumetric flask correctly according to the rules. A volumetric flask is a commonly used measuring device that accommodates the volume of a solution, which is mainly used to dispense a certain amount of solution to a volumetric device. However, in practice, it is often used to store solutions for a long time, especially alkaline solutions, which will erode the bottle wall and make the stopper stick and cannot be opened. The prepared solution can not be stored in the volumetric flask but should be poured into the reagent bottle in time. The reagent bottle should be washed twice with the prepared solution for 2 to 3 times.
3. Do not regularly adjust the measuring instruments such as volumetric flasks, burettes, and pipettes as required. Sometimes its value does not match the real volume, causing volume errors, causing systematic errors. Usually corrected every six months.
4. Unfamiliar with the capacity tolerance and standard capacity level of various gauges, the different types of capacity tolerances are different, which leads to the error caused by improper selection of the gauge. When it is usually required to accurately measure a certain volume of the solution, the pipette and the pipette are used, and the other measuring tools such as the measuring cylinder and the measuring cup cannot be used to cause an error.
Fourth, the basic operation of the glass instrument is wrong
1. 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 reagent for the jar, the liquid reagent for the fine bottle, the acid material for the glass stopper, the alkaline material for the rubber stopper, and the principle that the light is easily decomposed with the brown bottle (such as AgNO3, I2 liquid, etc.). This causes impurities or variations in the amount of the formula to cause errors.
When the reagent is taken, the stopper is not placed on the operation table according to the regulations, so that the reagent is contaminated, thereby affecting the measurement result.
2. When using the weighing bottle to weigh the sample, do not dry the weighing bottle at 105 °C first, then use it after cooling the constant weight; the dry weighing bottle is taken directly by hand instead of using dry and clean The strip is placed on the weighing bottle for access. Lead to the weighing bottle, affecting the accuracy of the weighing results.
3. When the standard solution is loaded into the burette, the standard solution concentration is changed or contaminated by means of a funnel or other container.
Before the measurement, the liquid level is not adjusted to the position of “0.00”. After the titration is started and finished, the solution attached to the inner wall can be read after flowing for 1 min to 2 min, and the volume error is immediately caused by the reading.
The timing of the titration is too fast so that the solution is discharged in a flowing state. Even when the end point is approached, the titration speed is not slowed down, causing the inspection error to occur at the end of the titration.
The reading (colorless or light solution) does not keep the line of sight of the eye and the lowest point of the concave surface of the solution in the burette; 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 burette, etc. Cause volume error.
4. When using the cleaned pipette for the first time, do not use the filter paper to absorb the water inside and outside the tip. Then use the removed solution to wash the pipette 2 or 3 times to ensure the pipetting. The solution concentration is unchanged.
When removing the solution, use the right thumb and middle finger to hold the top of the neck marking. Insert the pipette into the solution. It should not be too deep or too shallow. Too deep will cause too much solution to adhere to the outside of the tube. The accuracy of the volume; too shallow will often produce empty suction.
When placing the solution, make the tube vertical pipe dust against the inner wall of the container, let the solution in the tube flow naturally along the wall, wait for 10s~15s, then take out the pipette, do not blow out the solution remaining in the tip, because When correcting the pipette, the volume of the solution retained at the end has been considered, otherwise volume error is caused and the accuracy of the result is affected.
If you have any doubts or need more information, don’t hesitate to get in touch with WUBOLAB, the laboratory glassware manufacturer.
