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What is the difference between vacuum drying and general drying?

1. Application of heat-sensitive substances: the vacuum environment greatly reduces the boiling point of the liquid to be removed, so vacuum drying can be easily applied to heat-sensitive substances; General drying is not suitable for drying heat-sensitive substances.

2. Difference in drying time: for samples that are not easy to dry, such as powder or other granular samples, vacuum drying method can effectively shorten the drying time; In contrast, normal drying takes longer. Turn left | turn right

3. Whether there is any difference in residue after drying: various mechanical parts with complicated structure or other porous samples are cleaned by vacuum drying method, leaving no residual substances after being completely dried; General drying because the process is simple, easy to leave residual material.

4. Difference in safety performance: the vacuum drying method is safer: under vacuum or inert conditions, it completely eliminates the possibility of hot explosion of oxides; Powder samples are not blown or moved by moving air, as compared to normal dryness, which relies on air circulation.

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The difference between automatic burette and semi-automatic burette

Burette is a glass instrument that can accurately measure the consumption volume of titrant during titration. It is a thin glass tube with precise scale and uniform inner diameter. It can continuously release different volumes of liquid according to the needs and accurately read the volume of liquid.

Depending on the length and volume, burette can be divided into constant burette, semi-micro burette and micro burette.

The constant burette has a volume of 50mL and 25mL, with a minimum scale of 0.1ml and a minimum reading of 0.01ml. The semi-micro burette has a capacity of 10mL, with a minimum scale of 0.05ml and a minimum reading of 0.01ml. The structure is generally similar to that of a constant burette. The volume of the micro burette was 1mL, 2mL, 5mL and 10mL, with a minimum scale of 0.01ml and a minimum reading of 0.001ml. There is also a semi-micro semi-automatic burette, which can be added automatically, but titration still requires manual control.

Burette is generally divided into two types, acid burette and base burette

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High borosilicate glass tube main raw material

High borosilicate glass tube can take advantage of the conductive properties of glass in high temperature state and realize glass melting by heating from the inside of glass. In the glass tube, silica > 78%, boron oxide > 10%, silicon and boron content is very high.

1. Acid oxide raw materials: SiO2, B2O3, Al2O3 and other raw materials. SiO2 is the skeleton of the glass structure in silicate glass. It gives the glass high strength, good chemical stability, heat resistance and low expansibility, but will make the glass melt temperature increase, increase the viscosity. The reference materials of SiO2 are silica sand or sandstone or quartzite. Adding B2O3 to the glass can reduce the thermal expansibility of the glass, improve the refractive index, heat resistance and chemical corrosion resistance, reduce the glass viscosity when the temperature is high, and increase the glass viscosity when the temperature is low. The reference material for B2O3 is borax or boric acid. Adding Al2O3 to glass can reduce crystallization tendency, enhance chemical stability, increase strength and increase glass viscosity. The reference material is usually feldspar with K2O or Na2O and SiO2, also can be used industrial alumina. Cangzhou tianchang glass factory specializes in the production of various types of high borosilicate glass tube

2, alkali metal oxide raw materials: there are Na2O, K2O raw materials. Adding Na2O and K2O in glass can reduce the melting temperature and viscosity, but the chemical stability of glass will become worse. The reference materials are soda ash (Na2CO3) and potassium base (K2CO3).

3, alkaline earth metal oxide raw materials: CaO, MgO, BaO, ZnO, PbO raw materials. Adding CaO and MgO in glass can weaken the crystallization tendency of sodium silicon glass and enhance the chemical stability. At high temperature, it can reduce the glass viscosity and promote the melting and clarification of glass. However, when the temperature decreases, the viscosity increases quickly and the molding operation is difficult. The reference materials are limestone (CaCO3) and calcareous soil (MgCO3), or dolomite containing CaO and MgO. BaO and ZnO are often added to the glass to adjust the chemical stability and refractive index of the glass and other properties, the reference materials are often industrial ZnO and BaCO3, BaSO4 or Ba (NO3) 2. Adding PbO to the glass can significantly increase the refractive index and dispersion, so that the glass can absorb short wavelength rays. At the same time, the specific gravity increases, the melting temperature decreases, and the metal has good permeability. The reference materials for PbO are red lead and yellow lead or industrial lead nitrate.

In addition, broken glass is also a major raw material, often called clinker, which can be melted at lower temperatures, contributing to the melting of glass blends.

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What glass instruments are used in chemical experiments What are the raw materials for making glass

Glass has a long history and stable properties. It is an excellent material that has stood the test of time. It can not only be used for decoration, but also play an important role in various optical instruments. By using different processing methods, we were able to make the glass have different properties. Let me have a look at the glassware used in chemical experiments and the raw materials used to make glass.

 What glass instruments are used in chemical experiments

1. Conveying and intercepting devices, such as glass joints, joints, valves, plugs, pipes and rods, etc.

2. Containers, such as dishes, bottles, beakers, flasks, grooves, test tubes, etc.

3. Basic operating instruments and devices. Basic operations include absorption, drying, distillation, condensation, fractionation, evaporation, extraction, purification, filtration, liquid separation, stirring, crushing, centrifugation, gas generation, chromatography, combustion, combustion analysis, etc.

4. Measuring instruments, such as flow, specific gravity, pressure, temperature, surface tension and other measuring instruments, as well as measuring instruments, droppers, pipettes, syringes, etc.

5. Physical measuring instrument, such as measuring color, light, density, electrical parameters, phase transition, radioactivity, molecular weight, viscosity, granularity, etc.

6. Instruments for the determination of chemical elements and compounds, such as arsenic, carbon dioxide, elemental analysis, functional group analysis, metallic elements, sulfur, halogens and water.

7. Materials testing instruments, such as atmosphere, explosives, gases, metals and minerals, mineral oil, construction materials, water quality and other measuring instruments.

8. Food, medicine and biological analysis instruments, such as food analysis, blood analysis, microbial culture, microscope accessories, serum and vaccine tests, urine tests and other analytical instruments.

 What are the raw materials for making glass

Glass non-crystalline inorganic non-metallic materials, generally with a variety of inorganic minerals (such as quartz sand, borax, boric acid, barite, barium carbonate, limestone, feldspar, soda soda, etc.) as the main raw materials, plus a small number of auxiliary materials made. Its main components are silicon dioxide and other oxides. The chemical composition of ordinary glass is Na2SiO3, CaSiO3, SiO2 or Na2O·CaO·6SiO2, mainly composed of silicate compound salt, is a amorphous solid with irregular structure.

 The main raw materials for glass production are glass forming body, glass adjusting material and glass intermediate, and the rest are auxiliary raw materials. Oxides, intermediate oxides and oxides outside the network formed by the main raw materials directed into the glass; Auxiliary materials include clarifying agent, flux, emulsion agent, colorant, decolorizer, oxidizer and reducing agent.

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Standard operation and use of volumetric flask

Volumetric flask is mainly used to prepare accurate concentration of solution or quantitative dilution solution, often used with pipette, can be higher concentration of solution quantitative dilution into a lower concentration of solution.

 Inspection of volumetric bottles

 1. inspection of volumetric bottles check whether the bottle stopper is leaking. The method is: add water to the bottle near the mark line, cap the bottle stopper, hold the bottle stopper with the index finger of the left hand, hold the bottle bottom edge above the mark line with the fingertips of the right hand, stand the bottle upside down for 2min to see if it is leaking, and check with a small piece of filter paper. If it is watertight, stand the bottle upright, rotate the cork 180, and then stand on its head for 2min to check if it is watertight. In use, the bottle stopper should not be placed randomly, so as not to stain, make mistakes or break. Use a rubber band or string to tie the cork to the neck of the bottle. If it's a flat-topped plastic plug, place the plug upside down on the table.

 2. for the washing of volumetric bottle, wash it with tap water for 3 times first. After pouring water, if there are no beads on the inner wall, wash it with distilled water for later use. Otherwise, it must be cleaned with chrome-acid solution. The method is: first try to pour as much water as possible in the bottle, then pour an appropriate amount of lotion (250mL volumetric bottle, pour about 20mL lotion), tilt the volumetric bottle, make the lotion full of the inner wall, soak 10win left and right, and then slowly pour the lotion back to the original bottle. Then wash the volumetric bottle and its stopper with tap water. Each washing should be fully oscillated and the residual water should be exhausted as far as possible. Wash with distilled water 3 times. Water consumption depends on the size of the volumetric bottle, such as 250mL volumetric bottle, about 30mL for the first time, and about 20mL for the second and third time. Wash and set aside.

 3. use of volumetric bottles

 A) to prepare the solution with a volumetric flask, dissolve the solid in a small beaker, and then transfer the solution quantitatively to a cleaned volumetric flask. For quantitative transfer, take the glass rod in one hand and stick it 3cm - 4em into the bottle; Hold the beaker in one hand, the beaker's mouth is close to the glass rod, slowly tilt the beaker so that the solution flows down the glass rod. After pouring the solution, move the beaker up 1cm ~ 2cm along the glass rod upright, and put the glass rod back into the beaker, but not against the beaker mouth. Then rinse the beaker and the glass rod with a small amount of distilled water for 3-4 times, and the washing liquid is transferred to the volumetric bottle to complete the quantitative transfer. When adding water to about 3/4 of the volume of the volumetric bottle, hold the flat head of the bottle stopper between your right forefinger and middle finger, pick up the volumetric bottle and shake it horizontally so that the solution is mixed evenly at the first step. Continue to add water dilute, when the liquid level line about 1 cm distance, applied by dripping water dropper (note that the dropper stretch from people in the volumetric flask to the edge of meniscus coincided with the line tangent to cover the cork, use forefinger hold the cork top, the other four fingers caught bottleneck line above parts, with the other hand the fingertips hold bottle bottom edge, the volumetric flask back, to make the bubbles rise, will bottle oscillation several times, is up, once again turned to oscillation. Repeat this for more than 1O times so that the solution is thoroughly mixed. This process is called constant volume.

 B) if the solution is diluted with a volumetric bottle, use a pipette to remove the solution of a certain volume, put it into the volumetric bottle, dilute it to the mark line, and then mix it thoroughly. The operation is as above.

 C) the volumetric bottle is not suitable for long-term preservation of solution. If the solution needs to be preserved, it should be transferred to the reagent bottle. The reagent bottle should be rinsed 3 times with the solution in the volumetric bottle so as not to dilute the solution.

 D) flush the volumetric bottle with tap water immediately after use. When not used for a long time, the mouth of the mill should be washed and dried, pad with a small piece of paper.

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Standard operation and use of pipette

Pipette is used to measure the volume of liquid accurately. Under the temperature indicated, first make the lower edge of the menissima of the liquid tangent to the pipette line, and then let the liquid flow out according to a certain method of free flow, then the volume of the outflow of liquid and the volume marked on the tube is the same.

1.1before washing the pipette, the pipette shall be cleaned until only a uniform water film is left on the inner wall and no droplets are collected. Can be rinsed with tap water first, if still have water drop, can use chromate to wash fluid. The process is as follows: Washing ears ball, with his left hand wash index finger or thumb on the top of the ear, and the rest of the fingers natural holding washing ears ball, with the thumb and middle finger of right hand took the part of pipette and marking above, ring finger and little auxiliary took pipette, and insert the pipet tube tip lotion, wash ears ball in the air after discharge, the tight inserted inside the mouth pipette tip, slowly loosen pinched her ears ball, wash wash liquid suction slowly rise, to wash suction pipet volume 1/4, remove the washing ears ball, with right index finger hold the nozzle, leave the lotion, Turn the tube horizontally, hold the lower end of the tube with your left hand, slowly open your right index finger, turn the pipette and make the lotion fill the whole tube. When the washing liquid flows to the upper mouth 2am ~ 3am, erect the pipette so that the washing liquid is put back to the original bottle from the tip. Then rinse thoroughly with tap water, then wash with a small amount of distilled water for 3 times, washing method as before. Water consumption per time: to the extent that the liquid level rises to about 1/4 volume of the bulb.

1.2 use of pipette

A) before removing the solution, the water inside and outside the tip of the tube must be sucked up with filter paper, and then the solution to be removed is rinsed for 3 times. The method is: first, use the small beaker to be rinsed with the liquid to be rinsed for 3 times, then pour a small amount of the solution to be rinsed into the small beaker, and then use the ear-washing ball to suck the solution in the small beaker into the pipette. Each time, remove the pipette by 1/4 volume to rinse the pipette, and discard the used solution.

B) when the solution is removed, insert the pipette 1em - 2cm below the liquid level of the solution to be absorbed, and do not insert it too shallowly to avoid suction after the liquid level drops; Also do not insert too deep, in order to avoid pipette wall attached to excessive solution. During the suction process, attention should be paid to the position of the liquid level and the pipe tip, and the pipe tip should fall with the drop of the liquid level. When the liquid level reaches 1em ~ 2em above the mark line, remove the ear-washing ball quickly, and immediately plug the nozzle with the right index finger. Put down the ear-washing ball in the left hand, pick up the liquid test bottle, keep the line of sight level with the mark line, then slightly turn the finger of the right hand to make the liquid level slowly drop, until the meniscus level is cut with the mark line in the eye level, press the index finger immediately. Put down the test liquid bottle in the left hand, pick up the container receiving the dissolved liquid, tilt it about 45, make the pipette vertical, the tip of the tube tightly against the inner wall of the receiving container, loosen the index finger of the right hand, so that the solution will flow naturally along the wall. After the solution drops to the tip of the pipe, it should wait for about 15s, then take out the pipette and put it on the pipette rack. Don't leave them around to avoid contamination. Note that after the solution is released from the pipette, a small amount of dissolved liquid remains at the tip of the pipette. For this reason, unless the word "blowing" is specified, the residual liquid cannot be blown into the receiving container, because this part of volume is not included in the calculation of pipette volume in the production of the factory.

C) pipette shall be placed on pipette rack after use. If it is no longer used to remove the same solution in a short time, it should be rinsed immediately with tap water, then washed with distilled water, and then placed on the pipette rack.