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First, the specifications and use of commonly used glassware
The glassware commonly used in chemical testing laboratories is divided into two categories, one is glassware for containers such as test tubes, beakers, reagent bottles, etc.; the other is metering glass measuring devices for measuring liquid volume such as measuring cylinders, measuring cups, and pipetting Tube and so on. The volume measurement unit is millimeter; since the measurement condition of the measurement is based on 20 ° C, the words of mL and 20 ° C are marked on the gauge.
(a) graduated straw
The graduated pipette is a type of glass measuring device that uses a large amount of quantitative removal solution in the chemical testing laboratory. The specifications are 0.1, 0.2, 0.5, 1, 2, 5, l0mL and the like. According to whether it is necessary to blow out the liquid that the pipe tip cannot naturally flow out, the scale pipette is divided into two types: a complete outflow type and an incomplete outflow type. The so-called complete outflow is measured by the total volume of the solution injecting the straw. When using such a straw, the liquid remaining in the tip of the straw cannot be naturally blown out. Usually, the upper wall of the straw is marked with "blowing" and "TC'"; the measurement of the volume of the incompletely flowing straw does not include the liquid that the tip of the tube cannot naturally flow out at the end. When using such a straw, the liquid remaining at the tip of the tube cannot be blown out. The upper wall of the straw is often marked with The letter "TD" is the word.
When using the graduated pipette, insert the tip of the pipe into the liquid surface about 1cm. The scale on the pipette faces the operator. Use the earball to suck the liquid to the required amount of the mark. Slightly use the index finger to block the nozzle. Move to the liquid surface, vertical pipette, gently loosen the index finger, and slowly put the excess solution back into the reagent bottle. The lowest point of the liquid meniscus in the pipette is just tangent to the required amount of the mark, and is pressed with the index finger. Pipe, let the tip of the pipe touch gently on the bottle wall and stop slightly. The liquid adhering to the outer wall of the pipette flows into the bottle, then the pipette is moved into the container, and the index finger is released, so that the liquid in the straw can naturally flow out.
The specifications of the straw are many. According to different pipetting volumes, it is very important to select the correct size of the straw. If you use a 10mL pipette to draw 0.1mL solution or take 1.0mL and use a 0.5mL pipette to suck twice, etc., this incorrect pipetting method will cause artificially increased analytical error, resulting in inaccurate experimental results.
In addition, the accuracy of the different sections of the straw is also different. Generally, the lower measurement accuracy of the straw is worse than that of the upper part, so the lower part of the straw should be avoided as much as possible. For example, if a 0.6 mL solution is taken, a 1.0 mL pipette can be used, and the solution is aspirated to 1.0 mL, and the solution is placed at 0.4 mL. The solution is taken as the desired solution, and the remaining 0.4 mL of the solution is discarded.
(2) Measuring cylinder, measuring cup
The measuring cylinder has a cylindrical shape and is divided into two types: a mouth and a mouthless plug. The measuring cup is conical with a pouring nozzle. Measuring cylinders and measuring cups are often used to measure liquids that require less precise volume. Its capacity tolerance is roughly equivalent to its minimum division value. The cylinder is more accurate than the measuring cup. Specifications are 5, 10, 25, 50, 100, 250, 500, 1000, 2000mL and so on.
When the volume of the solution is measured by the measuring cylinder or the measuring cup, the reagent bottle is placed on the measuring cylinder mouth, and the reagent is slowly poured down to the required scale along the wall of the tube, and then the bottle is gradually erected to prevent the liquid droplets from flowing down the outer wall of the bottle, and vice versa from the measuring cylinder or the measuring cup. The same operation is also performed when pouring out the liquid.
(three) volumetric bottle
The volumetric bottle is referred to as a measuring bottle, which is a flat-bottomed round-shaped long-necked bottle. The bottle neck is engraved with a circular line scale to indicate the capacity. It has a grinding bottle stopper, which is a more accurate capacity measuring device. It is often used to prepare a certain volume of standard solution and set. For experimental use. The color of the measuring bottle is divided into brown and colorless and transparent. The former is used to prepare a solution to be protected from light, and the specifications are 5, 10, 25, 50, 100, 200, 250, 500, 1000, 2000 mL and the like.
When using a measuring bottle to prepare a solution, the solid (liquid) material is usually dissolved in a small beaker with a small amount of solvent, and then the solution is transferred to the measuring bottle along the glass rod, and the beaker is rinsed with a small amount of solvent for 2 to 3 times. Pour into the measuring flask, and then add the solvent and shake the measuring bottle to dilute the solution evenly. This avoids changes in volume after mixing. When diluting to the liquid level close to the marking line, wait for 30 seconds to 1 minute. After the liquid flow adheres to the inner wall of the upper part of the bottle neck, after the liquid surface bubble disappears, carefully add the solvent dropwise to the lowest point of the meniscus of the liquid surface. Just tangent to the marking. Rotate the measuring bottle repeatedly and shake it until the solution is fully mixed.
Note that the measuring bottle and its grinding port plug are sealed and the plug can not be mixed to prevent the liquid from flowing out when the measuring bottle is inverted and mixed. Glass measuring bottles cannot be used to store strong alkaline solutions (strong alkaline solutions can severely corrode glass). The cleaned measuring bottle cannot be dried by high temperature baking, otherwise the glass will be changed in volume due to high heat.
(4) Micro dosing device (pipette)
Micro-adhesives are also called micropipettes. They are divided into fixed and adjustable types. Fixed type refers to a liquidizer that can only remove a liquid of a specified capacity. Because of its variable factors, it is often used in standards. The solution is removed; the adjustable liquid applicator means that the volume of a pipette can be adjusted according to needs, and can be used in one device. Due to its convenient use and accurate volume, the micro-adjuster has been widely used in chemical testing laboratories. The specifications of the micro-adjuster range from 1mL to 10uL, which can be selected according to different needs. There are now 5mL~1mL liquid dispensers, which can replace glass straws to improve accuracy.
1. Principle When pressing the handle of the dosing device, the piston inside the dosing device moves in the piston cavity to discharge a certain volume of air in the piston cavity, and after releasing the pressing force, the piston is generated by the spring compression force. Negative pressure, inhaling a certain volume of liquid.
2. Use method: Put the plastic suction nozzle on the lower end of the liquid applicator and gently rotate it to ensure the seal. If it is an adjustable liquid applicator, it should be adjusted to the required suction volume mark. Before the formal aspiration, the dispenser should be vented and aired several times to ensure that the pressure inside and outside the piston chamber is consistent. Press the dosing handle to the first stop point, and immerse the nozzle in the liquid surface 2mm~3mm, then slowly release the pressure to reset it. After 1~2 seconds, remove the dosing device and add Move the liquid to the bottom of the container, slowly press the handle to the first stop point, wait 1~2 seconds; then press the handle to the second stop point to drain all the liquid in the suction nozzle, take out the liquid dispenser, and loosen the handle. To reset it, this is the whole process of one operation.
Second, the cleaning method of common glassware
(1) Commonly used washing liquids and their use methods
Synthetic detergent
Commercially available synthetic detergents such as laundry detergents, dishwashing detergents, and the like can be used to clean glassware. Its characteristics are low price, easy to use, and strong oil removal. When used, it is made into a 1%~2% aqueous solution, and the glassware to be cleaned is immersed in the detergent solution for brushing. It is worth noting that because the residual detergent often has a great influence on the experimental results, such detergent-washed utensils must be repeatedly rinsed with tap water.
2. Potassium dichromate lotion
The strong oxidative properties of potassium dichromate in a strong acid solution are used to remove dirt. The preparation method comprises the following steps: weigh 50 g of potassium dichromate and 50 mL of distilled water, and then dissolve 500 mL of concentrated sulfuric acid into the upper liquid slowly (do not pour the potassium dichromate solution into concentrated sulfuric acid), and add a glass rod while adding Stir carefully, let cool, bottling and plugging (to prevent concentrated sulfuric acid from absorbing water to reduce decontamination ability). The newly prepared lotion is reddish-brown and has strong detergency. When it is used repeatedly, it turns dark green, which means that the lotion has no oxidative washing ability. The chromic acid washing solution has a good decontamination effect, but the disadvantage is that the hexavalent chromium contaminates the water. Avoid chromic acid washes as much as possible, except for utensils where other detergents are not easily cleaned. It should be emphasized that the glassware should be dried before being placed in the lotion. Because the watering device puts the human lotion to make the solution green.
3.30% nitric acid solution
Suitable for the removal of oxidizable dirt, such as the washing of micropipettes and cuvettes.
4.45% urea solution
Suitable for washing utensils with protein stains.
5. Ethylenediaminetetraacetic acid disodium (EDTANa2) lotion
When used, it is formulated into a solution with a concentration of 5%~10%. By utilizing its ability to complex metal ions, heating and boiling can clean some heavy metal ions and calcium-magnesium salts attached to the glassware.
(two) washing method
Washing is the use of physical and chemical methods to remove the dirt attached to the glassware to achieve the purpose of cleaning the utensils.
1. Newly purchased glassware cleaning
The newly purchased glassware is accompanied by a free base, which should be immersed in a 2% hydrochloric acid solution for 2 to 6 hours to remove the free base. After taking out and washing with tap water, it was washed with a 2% synthetic detergent solution to remove oil stains. Take out and rinse with tap water repeatedly, then rinse with distilled water for 2~3 times.
2. Cleaning of used glassware
Rinse with tap water first, then brush with 2% synthetic detergent solution, rinse with tap water, and finally rinse with distilled water for 3 times.
3. Can not be brushed with a brush
Such as volumetric flasks, graduated straws, etc., can be rinsed with tap water first, then soaked in potassium dichromate wash solution overnight, taken out with tap water, and finally rinsed with distilled water 3 times, for the straw with a small diameter, must pay attention to Clean and rinse the inner wall of the straw.
(3) Drying method
Natural drying
It is a simple and practical drying method. Invert the washed utensils in a cabinet with clean gauze, or hang it upside down on a special rack and let it drain naturally. The method is suitable for vessels that are not urgently used or can not be baked at a high temperature, such as a measuring cylinder, a measuring cup, a volumetric flask, a straw, and the like.
2. Baking and drying
In addition to glass vessels that are deformed by high temperature, change volume, and affect the experimental results, other glassware such as test tubes, beakers, and flasks can be baked and dried in an oven at 120 ° C ~ 150 ° C for the glass for quantitative purposes. Measuring devices such as straws, measuring cylinders, etc., if urgently needed, can be dried in a medium-low temperature oven, the temperature should be less than 60 °C.
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The specifications, use and cleaning methods of glassware commonly used in physical and chemical testing are summarized!
The specifications, use and cleaning methods of glassware commonly used in physical and chemical testing are summarized!