How to dry glassware? Which method is better?

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The glass instruments used for chemical analysis should be washed and dried after each experiment before being set aside for use. Instruments used for different experiments have varying requirements regarding dryness. Generally, instruments such as beakers and Erlenmeyer flasks used in quantitative analysis can be used after being washed clean, while many instruments used in organic chemistry experiments or organic analysis require to be dry; some need to be free of traces of water, while others need to be completely water-free. Instruments should be dried according to these specific requirements. Cleaning standards for glass instruments: In chemical experiments, to prevent impurities from entering the reaction system and affecting the reaction conditions as well as the observation of experimental phenomena, it is necessary to use clean glass instruments. The cleaning of the instruments should be carried out immediately after each experiment. This is because, on the one hand, it is necessary to understand the nature of the contaminants at that time in order to adopt appropriate methods for removing them ； On the other hand, it also prepares for the next experiment. The general method for cleaning glassware is as follows: Select an appropriate brush, moisten both the brush and the glassware with water, then use the brush dipped in cleaning powder to scrub the inner and outer surfaces of the glassware (do not use cleaning powder on fluted glassware to avoid damaging the flutes). Once the dirt on the glassware has been removed, rinse it thoroughly with tap water. If a very high level of cleanliness is required, it is also necessary to rinse with a small amount of distilled water two to three times. A cleaned glass instrument should have no water droplets on its walls; if there are such droplets, it needs to be washed again. It should be noted that the instruments after washing cannot be dried with rags, filter paper, etc. Some reaction residues are difficult to clean with detergent; depending on the nature of the contamination, cheaper or recycled organic solvents can be used for soaking, or dilute acids and alkalis can be employed for cleaning. However, such methods should not be used indiscriminately to avoid waste and accidents (for example, when cleaning instruments containing residual bromine, using propane will result in the formation of a potent tear gas substance – propyl bromide). The residues on the instrument walls can be removed by soaking them in a cleaning solution and then washing them. Precautions for washing: 1. When washing instruments using normal methods, it is necessary to first wash your hands with soap, so as to prevent oil from your hands from sticking to the instruments and making cleaning more difficult. If the instrument has accumulated dust over time, rinse it first with clean water, and then clean or wash it using a detergent as appropriate. When rinsing with distilled water, use a wall-following rinsing method and shake thoroughly; the instrument after rinsing with distilled water should be neutral as checked with an indicator. 2. Glassware used for trace metal analysis should be soaked in a 1:1 to 1:9 HNO3 solution and then washed using standard methods. 3. When performing fluorescence analysis, glass instruments should not be washed with laundry detergent (as laundry detergent contains fluorescent brighteners that can cause errors in the analysis results). 4. When analyzing carcinogenic substances, an appropriate cleaning solution should be used for soaking, followed by washing according to standard methods. Common drying methods: Instruments used in chemical experiments not only need to be cleaned but often also need to be dried. The presence of water can sometimes affect the rate or yield of chemical reactions, and sometimes it even prevents such reactions from taking place. For experiments that generally do not require anhydrous conditions, simply invert the instrument to dry it before use ； For experiments requiring complete anhydrous conditions, the instrument must be dried in an oven or a hot air dryer. If it is needed urgently, the cleaned instrument can be rinsed with a small amount of ethanol or acetone, and then dried with a hair dryer. It must be specifically noted that regardless of the method used for drying the instrument, it must be allowed to cool to room temperature before it can be removed; otherwise, when a hot instrument is cooled suddenly, water vapor will condense on its walls. As long as it is not a volumetric instrument (measuring cylinder, burette, pipette, etc.), it can be dried. 1. For items that don’t need to be used immediately and only require moderate drying, rinse them with pure water, then place them upside down in a dust-free area to allow the water to drain, followed by natural drying. Instruments can be placed on shelves equipped with diagonal pegs and in glass cabinets with ventilation holes. 2. Dry the cleaned instruments to remove excess moisture, then place them in an electric oven for drying at a temperature of 105–120°C for about 1 hour. It can also be dried in an infrared lamp drying oven. This method is applicable to general instruments. Weighing flasks and similar items used for weighing should be placed in a desiccator to cool down and be stored there after drying. When drying instruments with solid glass stoppers and thick walls, it is important to raise the temperature gradually and not to use excessively high temperatures to avoid cracking; measuring devices should not be placed in an oven for drying. Rigid test tubes can be dried using an alcohol lamp, starting from the bottom with the mouth of the tube facing downward to prevent water droplets from flowing back and causing the tube to crack. Once no water droplets remain, turn the mouth of the tube upward to remove the water vapor. 3. Drying with hot (cold) air: For instruments that need to be dried quickly or for larger instruments that cannot be placed in an oven, drying by blowing air can be used. Typically, a small amount of ethanol or acetone is poured into the instrument from which water has been removed, and the solvent is shaken out until it is completely gone (the solvent should be recovered). Afterwards, a hair dryer is used – cold air is applied for 1–2 minutes first, until most of the solvent has evaporated; then hot air is used to dry the instrument completely. Finally, cold air is used to remove any remaining vapor, preventing it from condensing inside the container. This method requires good ventilation to prevent poisoning, and it is necessary to avoid contact with open flames to prevent explosions of organic solvents. What should be noted when drying in an oven? To be precise, no glass instruments should be placed in an oven for drying; the glass items that can be used in an oven are meant for holding substances rather than for measurement purposes. For example, beakers, flasks, and round-bottom flasks are suitable for drying, while glass measuring instruments (with scales) such as burettes, pipettes, and volumetric flasks are not suitable for drying. When drying glass, the temperature should not be too high; 100 degrees or less is ideal. When removing it, wear heat-resistant gloves to avoid burns. It is also best to wait until the oven temperature drops to 45 degrees or below (or to room temperature) before taking out the instrument, as removing it at high temperatures can cause the glass to crack due to sudden changes in temperature.