Security highlights in the lab

Chemical reagents preservation method

General rule: Solid reagents are usually placed in jars for easy access to the spoon or tweezers to remove solids. Liquid reagents are for easy pouring and to prevent volatilization. They are usually stored in jars. Some reagents, due to their special properties, tend to interact with the surrounding environment (including containers) and require special storage methods. Can be summarized as follows:

1. Substances that need to be kept sealed (l) Volatile substances should be sealed in reagent bottles and placed in a cool place. Such as concentrated nitric acid, concentrated hydrochloric acid, ammonia, halogen solution, liquid bromine and so on. In particular, liquid bromine is to be sealed after being “sealed”.

(2) The easily weatherable substances and the water-absorbable substances should be sealed and stored. Such as CaCl2, concentrated H2SO4, discoloration silica gel, CaO, Na2CO3·l0H2O, solid NaOH and so on. Substances that are easily hydrolyzed, such as magnesium nitride, require strict sealing.

(3) Substances that easily absorb CO2 in the air must be sealed and preserved, such as NaOH solution, Na2O2, lime water, Ca(C1O)2 (bleach powder), water glass (Na2SiO3 solution), and the like.

(4) Substances that are easily oxidized by O2 in the air must be kept sealed, such as ferrous salts, sulfites and the like. Among them, white phosphorus is easily oxidized to cause spontaneous combustion, so a large amount of white phosphorus is tightly sealed. A small amount of white phosphorus can be immersed in cold water. Cutting of white phosphorus should also be carried out under the surface of the water (to prevent the white phosphorus from burning with a knife when burning in the air). However, Na and K react with water and cannot be stored in water. Instead, they are stored in kerosene. Metal lithium is less dense than kerosene and is sealed in paraffin.

　　 2. Substances that need to be protected from light The substances that deteriorate due to light or heat need to be kept in brown bottles and sealed, such as HNO3, nitrate, H2O2, bromine water, chlorine water, etc.; AgCl, AgBr, and certain organic substances (such as aniline). Extremely sensitive materials are wrapped in black paper (cloth) and stored in a dark room.

3. Alkaline substances such as NaOH, which can easily interact with ordinary glass instruments, cannot be used with glass stoppers (caused by the formation of Na2SiO3); strong acids, chlorine water, bromine water, KMnO4, organic solvents, etc. can corrode the rubber, so you cannot use the eraser. Plug; hydrofluoric acid (HF) can not be filled with glass bottles.

4. When preparing or storing certain solutions, it is necessary to add appropriate substances to prevent oxidation and hydrolysis. Such as: FeSO4 solution, need to add iron nails (anti-oxidation) and dilute sulfuric acid (hydrolysis solution); SnCl2 solution needs to add tin particles (anti-oxidation) and dilute hydrochloric acid (hydrolysis solution).

5. Some solutions are prone to long-term preservation because they are easily oxidized. Such as hydrogen sulfate (H2S solution) and so on. It is worth noting that some substances have multiple properties and need to be considered in many ways. Such as nitric acid, both volatile (sealed), but also unstable (see light easy to decompose, placed in brown bottles), as well as strong oxidizing (can not use rubber stopper).

Dangers and prevention during the experiment

1. Experimental safety ● Fire prevention Chemicals contain many flammable substances that can cause fire if they are not used during use. Therefore, for flammables: 1 must be properly kept, placed in a counter, away from the source of fire. Combustibles, strong oxidants, potassium, sodium, calcium and other strong reducing agents should be properly kept; 2 the use of volatile combustibles, such as ethanol, ether, gasoline, etc. should prevent the escape of steam, add flammable products must stay away from fire; (3) Strict operating procedures and instrument selection should be used for heating or burning experiments. For example, condensers are used for distillation; 4 If flammable substances are left over after use, they must not be discarded at will. If residual metal sodium is used for ethanol treatment, white phosphorus should be used. Soak in cold water and so on. When using alcohol lights, we must pay attention to: 1 can not use a burning alcohol lamp to light another alcohol lamp; 2 can not blow out the alcohol lamp with the mouth; 3 can not add alcohol to the burning alcohol lamp; 4 lamp pot The alcohol inside cannot exceed 2/3 of the volume.

● Extinguishing If you accidentally cause a fire in your laboratory, you should immediately take the following measures: 1 Prevent the spread of fire: Remove flammables, cut off the power, and stop ventilation. 2 Fire extinguishing sources: Organic solvents such as alcohol spilled on the table to catch fire, and were covered with damp cloth, asbestos or sand. The fire could be extinguished with a fire extinguisher. Small areas of organic matter, potassium, sodium, white phosphorus, and other chemicals can be extinguished by sand.

Chemical fire precautions:

1 Chemicals that react violently with water cannot be saved by water, such as potassium, sodium, calcium, magnesium, aluminum, calcium carbide, PCl3, PCl5, sodium peroxide, strontium peroxide, calcium phosphide, etc. They react with water. Release hydrogen, oxygen, etc. will cause more fire.

2 Organic solvents with less water density, such as hydrocarbons such as benzene and petroleum, alcohols, ethers, ketones, esters, etc., can catch fire and cannot be extinguished with water, otherwise they will expand the burning area; organic solvents that are more dense than water and insoluble in water, If carbon disulfide and other fires can be extinguished with water, they can also be extinguished by foam fire extinguishers and carbon dioxide extinguishers.

3 The combustion in the reactor, if the open vessel can be covered with asbestos cloth. During distillation and heating, if the condensing effect is not good, the flammable vapor is ignited at the top of the condenser, and plugs or other objects must not be used to block the condensing nozzle. The heating should be stopped first, and then saved to prevent explosion.

● Preventing explosions Various combustible gases and air are mixed with certain explosion limits. Before igniting a gas, the purity of the gas must be checked first. In particular, hydrogen must be tested for purity prior to igniting hydrogen or heating a substance that reacts with hydrogen.

● The experiment of preventing the suction and burst heating of the preparation gas and passing the gas into the solution shall prevent the liquid from falling into the hot reaction vessel due to the sharp drop in the pressure in the reaction vessel. The coefficient of expansion of the glass is relatively small, uneven cooling and heating can cause the glass container to burst, and even injure the experimenter. To this end, pay attention to the following points: 1 heat as evenly as possible; 2 add a safety bottle after the reaction vessel; 3 use an undercut funnel to absorb gases that are easily soluble in water; 4 withdraw from the solution before the end of the experiment The catheter stopped heating again.

●Prevent harmful gases from contaminating air. Toxic gases such as Cl2, HCl, H2S, SO2, NO2 and other acid gases are absorbed by strong alkali solution (usually concentrated NaOH solution); CO, H2, gaseous hydrocarbons and other flammable gases, and ignited. NO is mixed with sufficient air before passing into alkali solution; NH3 is absorbed with sulfuric acid; experiments for preparing toxic gases should be conducted in a fume hood.

● To prevent bumps from heating organic substances, because their boiling points are generally low, once the temperature is too high, local overheating of the liquid will cause bumping. The reaction solution will even burst open the rubber plug to injure the experimenter. Therefore, in the reaction vessel, Put some broken tiles or zeolite.

● Operate in strict accordance with the experimental procedures The amount of the drug to be used should be as small as possible. For example, potassium metal reacts with water, and the amount of potassium is controlled to be mung bean-like. If the amount is too large, the reaction will be very intense and cause burning and even explosion. The volume of the reaction solution in the flask should generally not exceed half the volume of the bottle to prevent flushing out of the bottle. The heating should be controlled within the specified temperature range, especially organic reactions, such as the preparation of esters to use a small fire to heat and so on. Flammable reagents should be kept away from the heat source during the experiment; stoppers should be stoppered after taking reagents; dilute concentrated sulfuric acid must be slowly poured into the water along the wall and continuously stirred. When you smell the gas, you need to fan it by hand to let a tiny amount of gas float into the nostrils.

2. Accident handling methods ● Trauma First aid cotton wool or gauze to clean up the wound, if there is a piece of glass to be carefully removed, scrubbed with hydrogen peroxide or coated with red mercury, can also be coated with iodine (mercury and iodine can not be simultaneously Use), then apply external bandage.

● First-aid burns and burns can be used for cotton soaked 75% to 95% of alcohol lightly painted wounds, can also be used 3% to 5% of the KMnO4 solution light bruises to the skin becomes brown, and then smear ointment.

● Chemical burns to the eyes should be immediately flushed with plenty of running water while washing. For alkali burns, rinse with 20% boric acid solution; if acid burn, rinse with 3% NaHCO3 solution.

● When using strong corrosive chemicals such as concentrated acid and concentrated alkali, special care should be taken to prevent skin or clothing from being corroded. If the acid (or base) is on the test table, immediately neutralize with NaHCO3 solution (or dilute acetic acid), then rinse with water and dry with a rag. If there is only a small amount of acid or alkali droplets on the table, wipe it off with a damp cloth and rinse the cloth with water. If you inadvertently stick acid to your skin or clothing, rinse with more water immediately and rinse with 3% to 5% NaHCO3 solution. If it is alkaline solution on the skin, rinse with more water, and then coated with boric acid solution.

● Emergency bromine for other chemical burns: Mix with 1 volume of ammonia + 1 volume of turpentine + 10 volumes of ethanol. Phosphorus: First wash with 5% CuSO4 solution and wet with 1 g/L KMnO4 solution. Phenol: Wash with plenty of water, scrub with ethanol, and wash with soap and water.

3. Proper handling of waste liquids and waste residues after experimentation Most of the wastes from chemical experiments are harmful or toxic. They cannot be directly discharged into sewers. They can first be collected and stored in waste liquid tanks, and then can be centrally processed later. However, some waste liquids that can react with each other to produce toxic substances cannot be arbitrarily mixed, such as strong oxidants and hydrochloric acid, sulfides, combustibles, nitrates and sulfuric acids, organic substances and peroxides, phosphorus and strong bases (producing PH3), and nitrous acid. Salts and strong acids (producing HNO2), MnO2, KMnO4, KClO3, etc. cannot be mixed with concentrated hydrochloric acid; volatile acids and non-volatile acids.

Solid residues often have heavy metal salts, which can cause pollution to water bodies and soil. They must be disposed (usually converted into insoluble oxides or hydroxides) and then buried. When mercury is accidentally spilled on the ground, it must be covered with sulphur, cleaned up to mercury sulfide and properly buried. With the remaining inflammables such as sodium, potassium, and white phosphorus, oxidants KMnO4, KClO3, Na2O2, etc., volatile organics, etc., should not be discarded at will to prevent the occurrence of a fire. Toxic substances cannot be thrown at random after they are used.