The "wrong" and "right" in basic chemical experiment operations!

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[Repost] "Wrong" and "Right" in the basic operations of chemical experiments! 1． Errors in holding test tubes: Grab it with your hand or spread your ring finger and little finger ； Position up or down. 　　 　　Correct method: “Make a two-finger fist with three fingers." That is, hold the test tube with your thumb, index finger, and middle finger, and make a fist with your ring finger and little finger, which is somewhat similar to writing with a brush. Hold the upper middle part of the test tube with your fingers. 　　 　　 2． Errors in taking medicines: A. When taking powdered medicine, because the medicine spoon is large, it cannot go deep into the container when adding medicine, causing it to spill or stick to the inner wall of the container. However, it is not known that a V-shaped paper trough is used instead of a medicine spoon to deliver medicine into the container. B. When pouring liquid medicine, the mouth of the reagent bottle is not close to the mouth of the receiver, causing the medicine to flow out, and the label is not facing the palm of the hand, causing the label to be corroded. 　　 　　Correct method: A． Take powdered or fine-grained solids, usually with a medicine spoon or paper trough. When operating, do "one delivery, two vertical, and three bombs." (That is, the medicine is fed flatly into the bottom of the test tube, the test tube is held upright, and the handle of the spoon or paper slot is lightly pressed with your fingers. ) to make all the drugs fall to the bottom of the test tube. B. Tweezers are commonly used to remove lumpy or large granular solids. The operating instructions are "one horizontal, two flat, and three slow vertical." "That is, when adding block drugs to the test tube, you should first place the test tube horizontally, put the drug into the mouth of the test tube, and then slowly stand the test tube up so that the drug slowly slides along the tube wall to the bottom of the test tube. C. Use a narrow-mouth bottle to pour liquid medicines, and the operating instructions are "one discharge, two directions, three blows, and four flows." That is, first remove the cork of the reagent bottle and place it upside down on the table, then pick up the bottle, with the label on the bottle facing the palm of your hand, the mouth of the bottle close to the mouth of the test tube, and let the liquid slowly flow into the bottom of the test tube along the inner wall of the test tube. 　　 　　 3. Mistakes in using the rubber dropper: The middle finger and ring finger do not clamp the connection between the rubber head and the glass tube. ； Insert the dropper tip into the mouth of the receiver. 　　 　　Correct method: When clamping: Use your ring finger and middle finger to hold the joint between the rubber tip and the glass tube. Do not hold it with your thumb and index finger (or middle finger). This will prevent the rubber tip from falling off. When aspirating liquid: First squeeze the rubber tip with your thumb and forefinger to drive away the air in the dropper, then insert the glass tip into the reagent liquid, release your thumb and forefinger, the liquid reagent will be sucked in, and then lift the dropper. It is forbidden to squeeze the rubber tip inside the reagent to prevent the reagent from being contaminated by air and containing impurities. After absorbing the liquid, the glue head must be upward and cannot be placed flat, let alone the opening of the glass tip upward to prevent the glue head from being corroded. ； Do not place the dropper after absorbing the liquid on the experimental table to avoid contamination of the dropper. 　　 　　 4. What goes wrong when shaking a test tube filled with liquid: Hold the middle or lower part of the test tube and shake it. 　　 　　Correct method: The fingers should be "three fisted and two fisted", holding the middle and upper part of the test tube, so that the middle and lower part of the test tube is left open to observe the experimental phenomena inside the test tube. When shaking the test tube, use your wrist to swing without shaking your arm, and move the bottom of the test tube in an arc to oscillate the solution in the tube. Do not turn it up and down to prevent the liquid from splashing out. 　　 　　 5. Mistakes when using a pallet balance: A． Dial the game code directly by hand ； B. No or less paper on the tray ； C. Medicines placed on the wrong tray ； D． If there are too many medicines on the tray, take them out and put them back into the original bottles. ； E. After weighing, I forgot to set the scale back to zero. 　　 　　Correct method: The correct operation key is "before weighing the pallet balance, first set the scale to zero and observe whether the balance is level. ； If it is uneven, tighten the nut ； Place the same piece of paper on both sides, put the wet and rotten medicine in the container, put the weighing items on the left and the weight on the right, and use tweezers to pick up the larger items first. ； At the end, the weighing code comes as a substitute, the weighing is completed and recorded, and the weight is returned to the box and the weighing code is zero. I hope everyone will remember it." You should also pay attention when using: A When moving the cursor, hold the left end of the ruler with your left hand, and use tweezers with your right hand to gently move the cursor. ； B. If a certain mass of solid powder is weighed, a certain mass of weights is placed in the right pan, and the insufficient weight is supplemented by weights. After the mass is determined, solid matter is placed in the left pan, often followed by * * It is difficult to control the amount of medicine added during balancing. At this time, you should hold the medicine spoon containing the medicine with your right hand and touch your right wrist lightly with your left palm, so that a small amount of solids splash into the left plate and gradually reach equilibrium. If you accidentally put too much medicine on the tray, do not put it back into the original bottle after taking it out, but put it in the designated container. 6． Mistakes when using measuring cylinders: A． Hand holding measuring cylinder reading ； B. When reading, some look down and some look up. ； C. Some cannot select a measuring cylinder with an appropriate range based on the volume of liquid required. D． If you add too much liquid, use a dropper to suck it out. 　　 　　Correct method: When using a measuring cylinder, the smallest size measuring cylinder that can be measured at one time should be selected according to the volume of liquid required. The key points of operation are to "measure the liquid and keep the cylinder steady" ； Mouth to mouth, avoid leakage ； Add dropwise to the mark ； When reading, keep your sight level with the lowest point of the liquid level." If the amount of liquid added accidentally exceeds the scale, hold a measuring cylinder and pour a small amount into the designated container, and then use a dropper to drop up to the scale. 　　 　　 7. Errors in stirring operation when dissolving salt: A． Dissolve salt and make a clanking sound when stirring with a glass rod ； B. A glass rod stirs the liquid in the middle and upper part. 　　 　　Correct method: During operation, place the beaker flat on the table, first add solid salt, then add an appropriate amount of water, hold 1/3 of one end of the glass rod, and extend the other end of the glass rod to the middle of the liquid in the beaker or along the inner wall of the beaker. Alternately make a circular motion in clockwise and counterclockwise directions. The speed should not be too fast, and the force should not be too strong. The glass rod should not hit the inner wall of the beaker to make a clanking sound. 　　 　　 8. Filter operation error point: There are air bubbles between the leaking paper and the funnel wall, which affects the filtration speed. ； Holding the glass holder too high or too low ； When the lower end of the glass cup rests on the filter paper: One is not leaning lightly against the three layers of filter paper, and the other is using too much force to tilt the funnel. ； The burnt tip holding the liquid to be filtered rests against the middle or even upper middle part of the glass holder. 　　 　　Correct method: When attaching the filter paper to the funnel wall, press the filter paper with your fingers and moisten it with water to make the filter paper stick to the funnel wall and drive away the air bubbles between the filter paper and the funnel wall to increase the filtration speed. The filtering operation requires "one stick, two low and three rely". One post: The filter paper fits tightly against the funnel wall. Second low: The upper edge of the filter paper is lower than the funnel mouth, and the solution level is lower than the upper edge of the filter paper. Three things to rely on: The lower end of the funnel neck is close to the inner wall of the beaker that receives the filtrate, and the lower end of the draining glass rod is lightly against the third layer of filter paper. ； The mouth of the beaker to be filtered is placed against the middle and lower part of the glass rod. The middle and upper part of the glass rod should be held. 　　 　　 9. Instrument connection error point: Press the glass tube firmly into the rubber stopper or rubber tube ； Pull hard when taking it apart ； He held the bend of the pipe and used force to break the pipe, causing his hand to be punctured. 　　 　　Correct method: "The left hand has a large mouth, and the right hand holds it to insert, moisten it first, then turn it with a little force and insert it." That is, hold an instrument with a large mouth in your left hand, and hold the part close to the instrument to be inserted with your right hand. Wet it first, and then turn it with a little force to insert it. When inserting the rubber stopper into the mouth of the test tube, slowly turn the stopper to tighten it. The appropriate size of the plug is that the part inserted into the mouth of the tube is 1/3 of the plug. When disassembling, turn it with slight force in the opposite direction to that when installing. 　　 　　 10. Error points in checking the air tightness of the device: The order of operations is reversed (first hold the test tube wall, then immerse the test tube in the water) ； The device is leaking or there are no bubbles coming out of the pipe port, and I don’t know where to start to find out the cause. 　　 　　Correct method: First put one end of the tube into the water, and then put your hand against the container to heat it. As the air in the container expands due to heat, bubbles will escape from the mouth of the tube. After releasing the handle to cool down for a while, the water will rise along the tube to form a water column. This indicates that the device is airtight. Observe that there are no bubbles coming out of the catheter port. There are two reasons.: First, if you hold the container with your hands for too long, the gas will no longer expand after thermal expansion to a certain extent. This is not caused by air leakage. The rubber stopper should be removed, the test tube should be cooled slightly and retested. The second is that the device is leaking. First find the cause from the device connection, and then consider whether the connection sequence is correct.