This involves the maintenance and cleaning of experimental instruments.
Experiment is the basis of chemistry and an important part of chemistry teaching activities. The use, cleaning and maintenance of laboratory chemical instruments are related to the success rate of experiments. Students should master the correct and standardized use of commonly used chemical instruments and understand the general knowledge of maintenance and cleaning.
1 Maintenance of Common Electrical Instruments
(1) electronic balance
Electronic balance is an essential weighing tool in our chemical experiment. Students can basically master its usage, but the details and cleaning maintenance of the experiment are not in place. After the experiment, there are some substances left under the scale, and there are stains on the scale. The sensitivity and accuracy of the balance are reduced and the service life is shortened. Electronic scales must be preheated for 10 minutes before use, but some students weigh them directly after turning them on. The temperature of the weighed object must be the same as that of the balance, and objects that are too hot or too cold cannot be placed on the scales of the balance. Some volatile and corrosive reagents should be weighed in a closed container. When weighing objects, remember to close the side door of the balance, and clean up the weighing pan up and down and all corners in time after weighing. When the air is humid and the substance has formed scale, mechanical rust removal method should be adopted, that is, the rust layer on the parts should be removed by shoveling, scraping and scraping first, then polished and polished with sandpaper, and finally coated with a protective layer. After the experiment, close the side door, cover it with a balance cloth and store it in a dark and dry place.
(2) electrothermal constant temperature drying oven
The electrothermal constant temperature drying oven is a common instrument for drying articles in chemical experiments. The working voltage of the oven is 220V, and the temperature 100 ~ 1 10 degrees should not be too high. Flammable and volatile chemicals should not be put into the box, and the items in the box should be placed in the center of the partition, which will not affect the air circulation, so as to ensure the uniform temperature in the box. In the process of using the drying box, students can't touch the box and switch with wet hands. Whether there is any abnormality, smell, smoke, etc. during the normal operation of the drying box. Turn off the power supply immediately during use, and ask professionals to check and maintain it. Always wipe the pool wall and equipment surface, keep it clean and increase the transparency of the glass. If the drying oven is not used for a long time, the power cord should be unplugged to prevent the equipment from hurting people, and it should be operated regularly for 2-3 days according to the use situation to drive away the moisture in the electrical parts and avoid damaging related devices.
(3) Constant temperature water bath pot
Constant temperature water bath pot is mainly used for distillation, drying and concentration of chemicals in laboratory, and can also be used for temperature tests such as constant temperature heating. It is an essential tool for chemistry laboratory, analysis room, education and scientific research. Middle school students should know how to use it and pay attention to it, so that the experiment can be carried out smoothly. Don't turn on the power supply before adding water. It is best to add distilled water to avoid scaling, and don't add too much water to avoid water overflowing the pot when boiling. The amount of water in the pot should not be less than half, and the heating tube should not be exposed to the water; Do not heat without water or the water level is lower than the partition, otherwise the heating pipe will be damaged. Water cannot flow into the control box during water injection to prevent electric shock. If the constant temperature control fails, the silver contact on the controller can be polished with fine emery cloth. After use, take out the thermostat, turn off the power supply, drain the water in the box, and record the use of the instrument.
2 the use and maintenance of common glass instruments
(1) beaker
Beakers are the most commonly used reaction containers, which are used to hold liquids, prepare solutions and carry out simple chemical reactions, because their diameters are the same. But beaker can't replace measuring cylinder to measure liquid. When the beaker is heated, it should be padded with asbestos mesh. You can't directly heat the beaker with flame. Because the bottom of beaker is large, it can only be directly heated by flame to burn locally, which leads to uneven heating and bursting of glass. When the beaker is used to heat the liquid, the amount of the liquid should not exceed 1/3 of the beaker volume to prevent the liquid from overflowing when boiling. When heating, the outer wall of beaker must be dry. When heating corrosive drugs, a watch mirror can be covered on the beaker mouth to prevent the liquid from overflowing. Don't put the chemicals in the beaker for a long time to avoid falling into the dust and evaporating the water in the solution. In the process of dissolution or dilution, when stirring with a glass rod, do not touch the bottom or wall of the cup.
(2) test tube
A container used in a laboratory to hold a small amount of drugs and react with a small amount of reagents when heated. When filling solution, it shall not exceed 1/2 of the test tube capacity, and when heating, it shall not exceed 1/3 of the test tube capacity. Use tweezers to put the massive solid into the test tube, and the solid cannot directly fall into the test tube to prevent the bottom of the test tube from breaking. When heating, use a test tube clamp, which is clamped away from the nozzle 1/3. Don't point the test tube mouth at people. Do not directly heat the test tube, but preheat it first. When heating the test tube with solid, the nozzle is slightly downward, and when heating the liquid, it is inclined by about 45. When heating, keep the outer wall of the test tube free of water drops to prevent it from bursting due to uneven heating. Do not quench after heating to prevent the test tube from breaking. After heating, do not clean the test tube until it cools to room temperature. External flame should be used when heating.
(3) volumetric flask
The volumetric flask is mainly used to accurately prepare a solution with a certain molar concentration. It is a pear-shaped flat glass bottle with a slender neck and a frosted glass stopper. The bottleneck is engraved with a marking line. When the liquid in the bottle reaches the scale line at the specified temperature, its volume is the volume marked on the bottle. A volumetric flask cannot prepare a solution with a volume lower than its volume, that is, it can only prepare a solution with a volume as large as its volume. Check whether the volumetric flask leaks before use, and then rinse it with tap water and distilled water for later use. Dissolve the solute in the beaker and then transfer it to the volumetric flask. Dissolve the solute in the volumetric flask and control the amount of distilled water to dissolve the solute. When transferring, glass rods must be used to drain water. The volumetric flask cannot be heated. If the solute releases heat during dissolution, it should be transferred after the solution is cooled, because the flask will expand when the temperature rises, and the measured volume will be inaccurate. The total amount of solvent used to clean the beaker should not exceed the marking line of the volumetric flask. Once it is exceeded, it must be reconfigured. Transfer the prepared solution to reagent bottle for storage. The volumetric flask can only be prepared with solution, but not stored, because the solution may corrode the bottle body, thus affecting the accuracy of the volumetric flask. After the volumetric flask is used, it should be washed with water in time, the cork should be plugged, and a piece of paper should be sandwiched between the cork and the bottle mouth to prevent the cork from sticking to the bottle mouth. Finally, when recording the volume of solution, four significant figures (XXX.0mL) are generally reserved.
④ burette
The burette is a measuring cup instrument which can discharge an indefinite amount of liquid. It is mainly used to measure the volume of titrant in titration analysis. Accurate to 0.0 1 ml. A burette with a glass piston is an acidic burette, and a burette with a rubber tube with a glass ball in it is an alkaline burette. Acid burette and alkaline burette cannot be mixed. Acidic burette contains acidic substances and most neutral substances (especially strong oxidants), while alkaline burette contains alkaline substances (including alkali and alkaline salts). Check the burette for leaks before use. In case of leakage, the piston should be coated with vaseline oil again. Before filling the liquid, rinse it with lotion and water in turn, and wet the burette with the solution to be filled. Pour the working solution until it is filled above the zero mark. Pay attention to check whether the burette outlet pipe is full of solution, and if there are bubbles, remove them. When adjusting the liquid level, keep the liquid level at 0 or below a certain scale. During titration, the burette should be clamped vertically on the burette clamp. If an alkaline burette is used, the thumb and forefinger should hold the latex tube on the side where the glass beads are located. Don't squeeze glass beads or move them up and down. Drop by drop should be added continuously during titration, and only one drop or half drop should be added near the end point until the solution has obvious color change. When reading, hold the upper part of the burette without scale, keep the burette vertical, look directly at the concave surface of the solution, and read to the second place after the decimal point, which is estimated to be 0.0 1mL. After titration, the residual solution in the tube should be discarded and not poured back into the original bottle, then the burette should be cleaned and hung upside down on the iron frame.
3 Cleaning of common glass instruments
Glass instruments commonly used in the laboratory, such as beaker, test tube, burette, pipette, volumetric flask, etc. The instrument will be contaminated with oil, scale and rust. If it is not cleaned in time after use, it will cause errors in the results and even have a very bad impact on the life and performance of the instrument. Therefore, the glass instruments used in chemical experiments must be cleaned. Here are some cleaning methods for glass instruments.
I simple instruments with easily removable substances, such as test tubes. Beakers, etc. Wash with tap water first, then brush with synthetic detergent dip tube, and finally wash with tap water. When the instrument is inverted, a uniform water film is formed on the wall of the instrument, and it will be washed without flowing down.
Two. For oily glassware, first clean it with alkaline alcohol cleaning solution, then clean it with washing powder water or soapy water, and finally rinse it with tap water.
Three. For rusty vessels, soak them in (1+3) hydrochloric acid lotion, and then rinse them with clean water.
Four. For vaseline-stained vessels, first clean the vaseline, then wash it with washing powder or soap before cooking, and then rinse it with tap water after taking it out.
Verb (abbreviation of verb) Some glass instruments with fine and complicated structures, such as volumetric bottles and pipets, can not be brushed with a brush, but can be soaked in washing liquid for a certain period of time before cleaning.
Do not wipe the cleaned glass instrument with hands, cloth or paper to avoid re-contamination.
4 Maintenance and cleaning of common optical instruments
Optical instruments commonly used in the laboratory, such as spectrophotometer, refractometer prism, glass slide, etc. , are precision optical instruments. When using and maintaining, we must be careful and strictly follow the instructions. Never loosen the connecting parts of the instrument at will, and never drop or collide with the instrument to avoid damaging the optical parts and affecting the accuracy. There should be no hard impurities in the test sample. When testing solid samples, the surface of refractive prism should be prevented from being brushed or dented. After use, it is forbidden to directly put it into water for cleaning, so as to prevent water from entering the optical system pipeline. Open the prism and gently dry it with mirror paper. Under any circumstances, anything other than mirror paper is not allowed to touch the prism to avoid damaging its optical plane. The instrument should be stored in a dry, dust-free, oil-free, harmful, flammable and explosive place to avoid corrosion or mildew of optical parts.
Optical instruments are easily contaminated with oil, wet dirt, fingerprints, etc. This affects imaging and light transmittance. Firstly, the prism, plane mirror and lens of the refractometer are cleaned with distilled water. If there are stains on the mirror, you can clean it with a mixture of ethanol and ether. When cleaning, use a special mirror cleaning paper or cotton ball to dip a small amount of detergent, wipe it in one direction, and make a circular motion from the center of the lens. Never soak this kind of lens in cleaning agent to clean it. Do not forcibly wipe and clean the lens, otherwise it will scratch the antireflection film and damage the lens. After cleaning, dry it with lens paper and keep it away from light.