What should you pay attention to when using glass instruments such as graduated cylinders and beakers in chemical laboratories! JIANG JING
1. First, simply classify chemical laboratory instruments according to whether they can be heated:
A: Can not be heated: measuring cylinder, gas cylinder, funnel, thermometer, dropping bottle, watch glass, wide mouth bottle, narrow mouth bottle, etc.
B: Can be directly heated: test tube, evaporating dish, crucible, burning spoon
C: Indirect heating: beaker, flask, conical flask
2. The usage of the instrument is introduced below, please refer to:
(1) Test tubes are commonly used as: ①reaction container for a small amount of reagents; ②can also be used as a container for collecting a small amount of gas; ③or used as a small gas generator.
(2) The beaker is mainly used for: ① dissolving solid substances, preparing solutions, and diluting and concentrating the solution; ② It can also be used for the reaction between larger quantities of substances.
(3) Flask (round bottom flask, flat bottom flask):
①It is often used for the reaction between a larger amount of liquid; ②It can also be used as an installation gas generator.
(4) Erlenmeyer flasks are often used for: ① heating liquids; ② can also be used to install gas generators and bottle washers; ③ can also be used for drip containers in titration.
(5) Evaporating dish is usually used for concentration or evaporation of solution.
(6) The plastic dropper is used for pipetting and dripping a small amount of liquid.
Note: ①When using, the glue head is up and the nozzle is down (to prevent liquid reagents from entering the glue head and causing corrosion of the glue head or bringing impurities in the glue head into the test solution; ②The nozzle of the dropper cannot be inserted into the drip container ( Prevent the dropper from being stained with other reagents); ③After use, it should be washed immediately and inserted into a clean test tube. The unwashed dropper is strictly forbidden to absorb other reagents. ④The dropper on the dropper must be used with the dropper.
(7) Measuring cylinder is an instrument used to measure a certain volume of liquid.
Do not dilute or prepare a solution in the graduated cylinder, and never heat the graduated cylinder; ② perform chemical reactions in the graduated cylinder.
Note: When measuring liquids, choose the appropriate measuring cylinder according to the volume to be measured (otherwise it will cause a larger error). When reading, place the measuring cylinder vertically and stably on the table, and make the scale of the measuring cylinder match the inside of the measuring cylinder. The lowest point of the liquid meniscus remains at the same level.
(8) Tray balance is a kind of weighing instrument, generally accurate to 0.1g.
Note: The weighing object is placed on the left plate, and the weights are placed on the right plate in descending order. The weights must be used with tweezers, not directly by hand. The balance cannot weigh hot objects, and the weighed objects cannot be directly weighed. Put it on the tray, put paper of equal quality on both sides first, the deliquescent medicine or corrosive medicine (such as sodium hydroxide solid) must be weighed in glassware.
(9) The gas cylinder ① is used to collect or store a small amount of gas: ② It can also be used to react certain substances and gases. (The mouth of the bottle is sanded).
(10) Wide mouth bottle (the inner wall is sanded): often used to hold solid reagents, and can also be used as a gas scrubber
(11) Flasks: used to contain liquid reagents, brown flasks are used to contain substances that need to be protected from light. When storing alkaline solutions, reagent bottles should be rubber stoppers, not glass stoppers.
(12) The funnel is used to inject liquid into the narrow-mouthed container or to filter the device.
(13) The long-necked funnel is used to inject liquid into the reaction vessel. If it is used to prepare gas, the lower end of the long-necked funnel should be inserted below the liquid surface to form a "liquid seal" (to prevent gas from flowing from the long-necked hopper) Escape)
(14) The separatory funnel is mainly used to separate two immiscible liquids with different densities. It can also be used to drip liquid into the reaction vessel to control the amount of liquid
(15) The test tube clamp is used to hold the test tube and heat the test tube. When in use, it is sleeved from the bottom of the test tube and clamped to the middle and upper part of the test tube.
(16) The iron stand is used to fix and support a variety of instruments, and is often used for heating and filtering operations.
(17) Alcohol lamp:
① Check the core of the lamp before use. It is absolutely forbidden to add alcohol to the burning alcohol lamp;
②Never use a burning alcohol lamp to light another alcohol lamp (to avoid fire)
③The outer flame of the alcohol lamp is the highest, so the outer flame part should be heated first and then concentrated.
④ Prevent the wick from contacting hot glassware (to prevent glassware from being damaged)
⑤ At the end of the experiment, the lamp cap should be used to extinguish the lamp (so as to prevent the alcohol in the lamp from evaporating and leaving too much water in the lamp core, which not only wastes the alcohol but also is difficult to ignite), never blow it out with the mouth (otherwise it may cause the alcohol in the lamp to burn. Danger)
⑥ If alcohol burns on the table, immediately cover it with a wet cloth.
(18) The glass rod is used for stirring (accelerating dissolution) transfer, such as pH measurement.
(19) Burning spoon
(20) The high temperature thermometer that has just been used should not be rinsed with cold water immediately.
(21) The medicine spoon is used to take powder or small granular solid medicine. Wipe the medicine spoon with clean filter paper before each use.
3. Basic operation
(1) Access to medicines: "Three prohibitions" ①Do not touch the medicine with your hands; ②Do not taste the medicine with your mouth; ③Do not put your nostrils in the mouth of the container to smell the smell
Note: The medicines that have been taken out or used cannot be returned to the original reagent bottle and should be returned to the laboratory.
A: Access to solid medicine
Tweezers for taking block solids (specific operation: first put the container horizontally, put the medicine into the mouth of the container, and then slowly erect the container); when taking powdered or small granular medicines, use a medicine spoon or paper Slot (specific operation: first lay the test tube horizontally, carefully send the medicine spoon or paper slot containing the medicine into the bottom of the test tube, and then make the test tube upright)
B: Access to liquid medicine
When taking a small amount, you can use a plastic dropper. When taking a large amount, you can pour it directly from the reagent bottle. (Note: Put the cork upside down on the table with the label facing your hand to prevent reagent contamination or corrosion of the label. Hold the test tube diagonally , Make the bottle mouth next to the test tube mouth)
(2) Heating of substances Test tubes, flasks, beakers, evaporating dishes can be used to heat liquids;
Dry test tubes, evaporating dishes, crucibles can be used to heat solids
A: To heat the liquid in the test tube, the test tube is generally at a 45° angle to the table top. After preheating, the bottom of the test tube is heated together, and it must not be directed at anyone during heating.
B: Heat the solid in the test tube: The mouth of the test tube should be slightly downward (to prevent the generated water from flowing back to the bottom of the test tube, causing the test tube to rupture), first preheat and then concentrate the medicine heating
Note: There should be no water on the outer wall of the heated instrument. Wipe dry before heating to prevent the container from bursting; the bottom of the glass instrument should not touch the core of the alcohol lamp during heating to prevent the container from breaking. Burned hot containers cannot be rinsed immediately with cold water, nor can they be placed on the table immediately, they should be placed on asbestos nets.
(3) Filtration is a method of separating insoluble solids and liquids (that is, one soluble, one insoluble, and filtration must be used), such as the purification of crude salt, the separation of potassium chloride and manganese dioxide.
Operation points: "one sticker", "two low", "three rely"
"Yi Tie" means that the filter paper moistened with water should be close to the funnel wall;
"Second paper" means ① the edge of the filter paper is slightly lower than the edge of the funnel ② the filtrate level is slightly lower than the edge of the filter paper;
"Three leaning" means ① the beaker is close to the glass rod ② the glass rod is close to the edge of the three layers of filter paper ③ the end of the funnel is close to the inner wall of the beaker
(4) When assembling the instrument, generally proceed from low to high and from left to right.
(5) Check the air tightness of the device. First immerse the catheter in the water, and then cover the wall with the palm of your hand (phenomenon: bubbles emerge from the mouth of the pipe, and a water column will form in the catheter when the hand is removed.
(6) For the washing of glass instruments, if insoluble alkalis, carbonates, and alkaline oxides are attached to the instruments, they can be washed with dilute hydrochloric acid and then rinsed with water. If there is grease in the instrument, it can be washed with hot soda ash solution, or with washing powder or decontamination powder. The standard for cleaning is: the water on the inner wall of the instrument neither gathers into water droplets nor flows down in streams, and when a water film is evenly attached, it indicates that it has been washed.
(7) Common accident handling methods
A: When using the alcohol lamp, if the alcohol burns accidentally, use a damp cloth immediately.
B: The acid is accidentally spilled on the table or on the skin and rinsed with sodium bicarbonate solution.
C: If the alkaline solution is accidentally spilled on the table, it should be rinsed with acetic acid. If it is accidentally spilled on the skin, it should be rinsed with boric acid solution.
D: If concentrated sulfuric acid is accidentally spilled on the skin, do not rinse with plenty of water first.
4. Gas production and collection
(1) Generating device for common gas
A: The solids react with each other and need to be heated. O2 equipment (NH3, CH4) is used; alcohol lamps must be used.
(2) Collection methods of commonly used gases
A: Drainage method is suitable for gas that is difficult or insoluble in water and does not react with water. The pipe is slightly extended into the bottle, (CO, N2, and NO can only be drained)
B: The upward exhaust method is suitable for gases with a higher density than air (CO2, HCl can only be used with upward exhaust method)
C: The downward exhaust method is suitable for gases with a density smaller than air
Exhaust method: the tube should extend into the bottom of the bottle
5. Full inspection of gas:
O2 full inspection: use a wooden strip with embers on the bottle mouth.
CO2 full inspection: put a burning wooden stick on the bottle mouth. The method to prove CO2 is to use clarified lime water.
6. (1) The test tube clamp should be clamped in the upper middle part, and the iron clamp should be clamped at 1/4 of the test tube opening.
(2) The liquid in the test tube during heating shall not exceed 1/3 of the volume of the test tube, and the liquid in the test tube during reaction shall not exceed 1/2 of the volume of the test tube.
(3) When using a flask or conical flask, the volume shall not exceed 1/2 of its volume, and the volume of solution when evaporating the solution shall not exceed 2/3 of the volume of the evaporating dish; the alcohol in the alcohol lamp shall not exceed 2/3 of its volume , And shall not be less than 1/4 of its volume.
(4) When washing the test tube, the water in the test tube is 1/2 of the test tube (half test tube water); the liquid in the gas washing bottle is 1/2 of the bottle; if the amount is not specified, a small amount should be taken, and the liquid should be 1 ——2ml, the solid only needs to cover the bottom of the test tube; when heating the liquid in the test tube, the test tube is generally at a 45° angle with the tabletop, and when heating the solid in the test tube, the test tube mouth is slightly inclined downward.
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