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Contents of this article
- What are the methods and precautions for using pipettes
- DingTalk Online Course Process and Precautions
- Requirements for waste collection What to pay attention to
1. What are the methods and precautions for using pipettes
1. What is the method for oiling an acid burette?
Remove the piston, dry the inner wall of the piston and plug sleeve with clean paper or cloth, dip a small amount of Vaseline with your fingers and apply a thin layer of Vaseline on both ends of the piston Do not apply Vaseline on both sides of the piston hole to avoid blocking the piston hole. After coating, put the piston back into the sleeve, rotate the piston in the same direction several times to make the Vaseline evenly distributed and transparent, and then cover it with a rubber ring. , fix the piston in the plug sleeve to prevent it from sliding out.
Close the piston, fill in distilled water to a certain mark, and stand the burette upright for about 2 minutes. Carefully observe whether the liquid level on the mark drops and whether there are any water drops dripping from the lower end of the burette. , and whether there is water seeping out of the piston gap, then rotate the piston 180° and wait for 2 minutes before observing. If there is water leakage, dry it and re-oil it.
Fill distilled water to a certain mark, stand the burette upright for about 2 minutes, and carefully observe whether the liquid level on the mark drops, or whether there are water drops dripping from the lower end of the burette. , if there is water leakage, you should replace the glass beads in the hose, choose a suitable size and smooth one and try again. If the glass beads are too small or not smooth, water may leak, and if the glass beads are too large, it will be inconvenient to operate.
Before loading, the standard solution in the bottle should be shaken well so that the water condensed on the inner wall of the bottle is mixed into the solution. In order to remove the remaining moisture in the burette and ensure the concentration of the standard solution The burette should be rinsed with this standard solution 2 to 3 times, about 10mL each time, and a small amount (about 1/3) should be released from the lower mouth to wash the tip part. The piston should be closed, hold the buret horizontally, and turn it slowly. , causing the solution to contact the inner wall of the tubeContact everywhere, and finally pour out the solution from the mouth of the tube and discard it, but do not open the piston to prevent the grease on the piston from rushing into the tube. Try to empty it before washing it a second time, and rinse the tip part every time. After washing it 2 to 3 times, you can load the standard solution to above the \”0\” mark.
For an alkaline burette, the hose should be bent upward, and the glass beads should be squeezed hard to make the solution spray out from the tip to eliminate air bubbles. The bubbles in alkaline burettes are usually hidden near the glass beads. You must check with the light whether the bubbles in the tube are completely eliminated. After the bubbles are eliminated, adjust the liquid level to 0.00mL or record the initial reading.
During titration, the tip of the burette should be inserted 1 to 2cm below the mouth of the conical bottle (or beaker mouth). The titration speed should not be too fast. It is advisable to drop 3 to 4 drops per second. Do not let it flow down into a liquid column. Shake while dripping. Make a circular motion in the same direction and do not vibrate back and forth as this will cause the solution to splash out. When the end point is approaching, add 1 drop or half a drop and blow a small amount with a washing bottle to rinse the inner wall of the Erlenmeyer flask so that all the attached solution flows down. Then shake the Erlenmeyer flask and observe whether the end point has been reached. If the end point is not reached, continue titration until the end point is accurately reached.
(1) After injecting or releasing the solution, you need to wait 30s to 1min before reading;
(2) The burette should be clamped vertically on the titration table for reading or the upper end of the burette should be held vertically with two fingers before reading;
(3 ) For colorless or light-colored solutions, the actual lowest point of the lower edge of the meniscus should be read. For colored solutions, the line of sight should be tangent to the highest points on both sides of the liquid surface. The same standard should be used for the first and final readings.
(1) After using the buret, pour out the remaining solution in the tube, wash it with water, fill it with distilled water to above the mark, and put a large test tube on the mouth of the tube. In this way, there is no need to clean it with lotion before next use;
(2) When the acid burette is not used for a long time, the piston part should be padded with paper, otherwise, the time After a long time, the stopper becomes difficult to open. When the alkaline buret is not in use, the hose should be unplugged and dipped in talcum powder to preserve it.
Both pipettes and pipettes can be washed with tap water, and then washed with distilled water. When they are dirty (when there are water beads hanging on the inner wall), chromic acid cleaning solution can be used Wash.
10. What is the method for washing pipettes or pipettes with washing solution?
Hold the pipette or pipette in your right hand, insert the lower opening of the pipe into the lotion solution, hold the ear cleaning ball in your left hand, first press out the air in the ball, and then connect the tip of the ball to the pipette or pipette Open the top of the tube, slowly release the fingers of your left hand, and slowly suck the lotion into the tube until it rises above the scale. After waiting for a while, put the lotion back into the original bottle.
Pinch the upper end of the pipette or pipette with the thumb and middle finger of your right hand, and insert the lower opening of the pipe into the solution to be taken. Do not insert it too shallowly or too deeply. Too shallow will cause aspiration. , suck the solution into the ear cleaning ball to make the solution dirty. If it is too deep, too much solution will stick to the outside of the tube
12. Use a pipette and. What are the precautions for burettes?
(1) Pipettes and pipettes used in precision analysis are not allowed to be dried in the oven;
(2) Pipettes and volumetric flasks are often used together, so the relative volumes of the two are often calibrated before use;
(3) In order to reduce measurement errors, the pipette should start from the top scale as the starting point every time and release the required volume downwards, instead of absorbing as much volume as it releases.
Before use, check whether the stopper of the volumetric flask is tight. To do this, you can put tap water in the bottle near the marking line, cover the stopper, and press the stopper with your hand. , turn the volumetric flask upside down and observe whether there is water seeping out of the mouth of the bottle. If there is no leakage, stand the bottle upright, turn the stopper about 180°, and then turn it upside down again. In order to prevent the stopper from being lost or messed up, plastic strings are often used to tie it up. Tie to the bottleneck
(1) In analytical work with high precision requirements, volumetric flasks are not allowed to be dried or heated in an oven;
(2) Do not use volumetric flasks to store prepared solutions for a long time;
(3) Volumetric flasks When it is not used for a long time, it should be washed and the stopper should be covered with paper to prevent the stopper from being opened after a long time.
15. Chemical reagents are divided according to their uses. Which ones?
It is divided into the following categories: general reagents, reference reagents, organic reagents for inorganic ion analysis, chromatographic reagents and preparations, indicators and test strips etc.
(3) Good stability, not easy to absorb water and not easily oxidized by air.etc.;
(4) The larger the molar mass, the more weighing, and the weighing error can be reduced.
17. What are the methods for expressing the concentration of general solutions?
Mass percent concentration, volume percent concentration, mass volume percent concentration.
18. Briefly describe what two changes occur during the dissolution process of substances?
One is that solute molecules (or ions) overcome their mutual attraction to diffuse between water molecules, that is, a physical change, and the other is that solute molecules (or ions) and water molecules attract each other and combine to form hydrated molecules, which is a chemical change.
19. How will solutions stored in glass bottles change over time?
It will cause the solution to contain sodium, calcium, and silicate impurities or cause certain ions in the solution to adsorb to the glass surface, reducing the concentration of the ions in the solution. .
20. How to open volatile reagent bottles in summer and how to operate them?
First of all, do not point the mouth of the bottle towards your face, and then soak the bottle in cold water for a period of time to avoid dangerous impact of gas and liquid in the bottle due to high room temperature. , the stopper should be tightly closed after taking the reagents, and bottles that release toxic and odorous gases should also be sealed with wax.
21. What are the methods to improve the accuracy of analysis?
Choose appropriate analysis methods, increase the number of parallel measurements, and eliminate systematic errors in measurement.
Features: Under certain conditions, the absolute value of the error in a finite number of measurements will not exceed a certain limit. Positive and negative accidental errors of the same size will almost never exceed a certain limit. There are equal chances of occurrence, small errors have more chances, and large errors have less chance.
Elimination method: increase the number of measurements, repeat multiple parallel tests, and take the average value. In this way, the positive and negative accidental errors can cancel each other out, and while eliminating the systematic errors Under the premise, the average value may be close to the true value.
Cause: A instrument error B method error C reagent error D operational error;
Elimination methods: do blank tests, calibrate instruments, control tests;
24. Both accuracy and precision relationship?
In order to achieve high accuracy, first of all, the precision must be high. However, high precision does not mean that the accuracy is also high, because it may There are systematic errors in the measurement. It can be said that precision is a prerequisite for ensuring accuracy.
Systematic error is also called measurable error. It is caused by some common reasons in the analysis process. In repeated measurements, it will appear repeatedly, which is harmful to The impact of the analysis results is relatively fixed.
26. Why do new glass electrodes need to be soaked for more than 24 hours?
Only when the glass membrane is soaked in water and the surface of the glass membrane swells to form a hydration layer can the sensitivity to H+ be maintained. In order to reduce the asymmetric potential small and stable.
27. During colorimetric analysis, how to control the absorbance values of the standard solution and the test solution to be between 0.05 and 1.0?
(1) Adjust the concentration of the solution. When the content of the component to be measured is high, the weighing amount can be smaller, or the solution can be diluted to control the absorbance of the solution. Between 0.05 and 1.0;
(2) Use cuvettes with different thicknesses. Since the absorbance A is directly proportional to the thickness of the cuvette, the ratio increases. The thickness of the color dish also increases the absorbance value.
(3) Select a blank solution. When the chromogen and other reagents are colorless and there are no other colored ions in the tested solution, distilled water can be used as the blank. Solution, if the chromogen itself is colored, distilled water with chromogen added should be used as the blank. If the chromogen itself is colorless, but there are other colored ions in the measured solution, the measured solution without chromogen should be used as a blank.
28. Why do new glass electrodes need to be soaked for more than 24 hours?
Only when the glass membrane is immersed in water and the surface of the glass membrane swells to form a hydration layer can the sensing sensitivity to H + stirring be maintained. The symmetric potential decreases and reaches stability.
29. During colorimetric analysis, how to controlAre the absorbance values of the prepared standard solution and test solution between 0.05 and 1.0?
(1) Adjust the concentration of the solution. When the content of the component to be measured is high, the weighing amount can be smaller, or the solution can be diluted to control the absorbance of the solution. Between 0.05~1.0.
(2) Use cuvettes with different thicknesses. Because the absorbance A is proportional to the thickness of the cuvette, therefore, increase the absorbance value of the thickness of the cuvette. also increased.
(3) Select a blank solution. When the chromogen and other reagents are colorless and there are no other colored ions in the tested solution, distilled water can be used as the blank. Solution, if the chromogen itself is colored, distilled water with chromogen added should be used as the blank. If the chromogen itself is colorless, but there are other colored ions in the measured solution, the measured solution without chromogen should be used as a blank.
The standard addition method is to add different amounts of standard solutions to several sample solutions, and then measure the absorbance and draw the absorbance according to the steps of drawing a standard curve. —Add the concentration curve and use extrapolation to find the concentration of the sample solution.
31. What are the following conditions that must be met to perform titration analysis?
(1) There must be an analytical balance for accurately weighing substances and vessels for measuring the volume of solutions;
(3) There must be an indicator to accurately determine the theoretical end point.
33. What are the following conditions that must be met to perform titration analysis?
(1) There must be an analytical balance for accurately weighing substances and vessels for measuring the volume of solutions;
(3) There must be indicators that accurately determine the theoretical endpoint.
It is divided into four categories, acid-base titration, complex titration, redox titration, and precipitation titration.
Answer: Routine analysis refers to the daily analysis performed by general laboratories to cooperate with production, also known as routine analysis. In order to control the normal progress of production, analysis results need to be reported quickly. This routine analysis is called quick analysis or in-process analysis.
When different units dispute the analysis results, the relevant units are required to conduct accurate analysis using specified methods.Analysis to determine the reliability of the original analysis results. This type of analysis is called arbitration analysis.
37. Briefly describe the main differences between photoelectric colorimetry and absorption photometry?
The main difference is the way to obtain monochromatic light. The photoelectric colorimeter uses a filter to split the light, while the spectrophotometer uses a prism or grating to split the light. , a prism or grating disperses the incident light into spectral bands, thereby obtaining monochromatic light in each band with higher purity and narrower wavelength range.
The basic principle of absorbance photometry is to pass mixed light through a grating or prism to obtain monochromatic light, let the monochromatic light pass through the colored solution being measured, and then project it onto A current signal is generated on the photodetector, and the absorbance and transmittance are displayed by the indicating instrument.
The method of using the photoelectric effect to measure the intensity of light transmitted through a colored solution to determine the content of the measured substance is called photoelectric colorimetry.
40. What are the five main components of photoelectric colorimetry?
Light source, filter, cuvette, photocell, galvanometer.
41. How to obtain the standard curve for measuring substance content by absorbance photometry?
First prepare a series (5 to 10) of standard solutions of different concentrations, and measure their absorbance A (or light transmittance) one by one at the maximum absorption wavelength of the solution. (rate T%), then use grid paper to draw a graph with the solution concentration as the abscissa and the absorbance as the ordinate. If the absorption of light by the measured substance complies with the light absorption law, a straight line passing through the origin must be obtained, that is, standard curve line.
42. During colorimetric analysis, how to control the absorbance values of the standard solution and the test solution between 0.05 and 1.0?
(1) Adjust the concentration of the solution. When the content of the component to be measured is high, the weighing amount can be smaller or the solution can be diluted to control the absorbance of the solution at 0.05 -1.0;
(2) Use cuvettes with different thicknesses. Since the absorbance A is proportional to the thickness of the cuvette, the absorbance value will also increase as the thickness of the cuvette increases;
(3) Select the blank solution, when The chromogen and other reagents are colorless, and there are no other substances in the solution being tested.When using color ions, distilled water can be used as the blank solution. If the chromogen itself has color, distilled water with chromogen added should be used as the blank solution. If the chromogen itself is colorless, but there are other colored ions in the measured solution, the measured solution without chromogen should be used as a blank.
43. What are the properties of glass and what are its main chemical components?
It has high chemical stability, thermal stability, good transparency, certain mechanical strength and good insulation properties. Its chemical components are mainly SiO2, CaO, Na2O, and K2O.
(1) Before use, the new filter should be cleaned with hot hydrochloric acid or chromic acid washing liquid while suction filtration, and then washed with distilled water. It can be placed upright Or turn it upside down and wash it repeatedly with water. (2) Use appropriate detergents for different sediments to first dissolve the sediment or invert the sediment to wash it with water, then rinse it with distilled water, dry it at 110°C, and then store it in a dust-free cabinet or covered container. Otherwise, the accumulated dust and sediment will clog the filter holes and it will be difficult to clean them.
Before cleaning the volumetric flask or colorimetric tube, it is best to use a small string or a thin plastic sleeve to fasten the stopper and tube opening to avoid breaking the stopper. Or they may be confused with each other. For grinding instruments that need to be stored for a long time, a piece of paper should be placed between the plugs to prevent them from sticking over time. Burettes that have not been used for a long time should be covered with paper after removing the Vaseline, and tie the piston with a rubber band for storage. If there are grains of sand between the grinding plugs, do not turn it hard to avoid damaging its accuracy. For the same reason, do not scrub the grinding area with detergent.
Generally speaking, the sampling error is often greater than the analysis error. Therefore, it is very important to master some basic knowledge of sampling and sample preparation. If the sampling and sample preparation methods are not accurate, Correct, even if the analysis work is done very carefully and correctly, it is meaningless, and sometimes even brings very bad consequences to production and scientific research.
Maximum weighing, also known as maximum load, indicates the maximum value that the balance can weigh. The maximum weighing of the balance must be greater than the possible mass of the object being weighed.
For chemical products with relatively uniform composition, any part can be taken as an analysis sample. When the batch size is large, the sampling percentage should be determined, and a part of each part should be taken out and mixed as an analysis sample. Sample.
(1) The sample should be completely decomposed, and the treated solution should not retain fines or powder of the original sample;
(2) There should be no volatilization loss of components to be measured during the decomposition process of the sample;
(3) The component to be measured and interfering substances should not be introduced into the decomposition process.
According to their different volumes, they are divided into constant and semi- Micro and micro burettes can be divided into ordinary burettes and automatic burettes according to their different structures.
51. How to adjust pipettes or pipettes. Liquid level?
Lift the pipette or pipette up and away from the liquid level, with the end of the tube still leaning against the inner wall of the container holding the solution, and the tube body still Stand upright, slightly relax your index finger, and allow the solution in the tube to slowly flow out from the lower opening until the bottom of the meniscus of the solution is tangent to the marked line. Immediately press the opening of the tube with your index finger, remove the droplet at the tip against the wall, and remove the pipette. Pipe or pipette, insert into the container that holds the solution
52. How to release the solution from the pipette or pipette?
If the container for receiving the solution is an Erlenmeyer flask, the Erlenmeyer flask should be tilted, the pipette or pipette should be upright, and the lower end of the tube should be close to the inner wall of the Erlenmeyer flask. Release your index finger and let The solution flows down the wall of the bottle. After the flow is finished, the tip of the tube touches the inner wall of the bottle for about 15 seconds, and then the small amount of solution remaining at the end of the tube cannot be forced out because of the calibration pipetting. tube or pipette, the volume of solution retained at the end has been taken into account.
During the transfer process, insert a glass rod into the volumetric flask and tighten the beaker mouth. Use the glass rod to slowly let the solution flow in along the glass rod. The lower end of the glass rod should be close to the inner wall of the bottle neck, but not too close to the bottle mouth to avoid overflow of the solution. After the solution flows out, lift the beaker up slightly along the glass rod and stand upright. , let a drop of solution attached to the mouth of the beaker flow back into the beaker, and wash it with a small amount of distilled water 3-4 times. The washing liquid is transferred and merged into the volumetric flask according to the above method.
After the solution is transferred into the volumetric flask, add distilled water. When it is diluted to about 3/4 of the volume, shake the volumetric flask flat several times for preliminary mixing. This can avoid volume changes after mixing. Then continue to add distilled water. When approaching the marking line, add it drop by drop carefully until the meniscus of the solution is tangent to the marking line.
Press the stopper with your left index finger. , hold the tip of your right finger against the bottom edge of the bottle, turn the volumetric flask upside down and shake it, then turn it over again to still make the bubbles rise to the top. Repeat this 15-20 times to mix well.
Weigh a certain volume of water, and then convert the mass of water into volume based on the density of water at that temperature.
57. The burette is clogged with grease. How to deal with it?
If there is old grease clogged in the piston hole, you can use a thin metal wire to gently remove it. If the tip of the pipe is clogged with grease, you can first fill the whole pipe with water, and then Place the tip of the tube in hot water to melt it and suddenly open the plunger to flush it away.
(3) To ensure that the reagents are not contaminated, a clean horn spoon should be used to take out the reagents from the reagent bottles. Do not pour the reagents back into the original bottles;
(4) Do not point your nose at the mouth of the reagent bottle and inhale sharply, and never use your tongue to taste the reagent.
(1) The solution used in the analysis experiment should be prepared with pure water, and the container should be washed with pure water more than three times;
(2) The solution must be contained in a reagent bottle with a stopper;
(3) Each bottle of reagent must be labeled with the name, specification, concentration and Label with preparation date;
(4) When storing the solution, care should be taken not to cause the solution to deteriorate;
\”>(5) When preparing sulfuric acid, phosphoric acid, nitric acid, hydrochloric acid and other solutions, the acid should be poured into the water;
(6) Do not touch corrosive substances with your hands And highly toxic solutions, highly toxic waste liquids should be detoxified and cannot be poured directly into the sewer;
(7) You should be familiar with the preparation methods of some commonly used solutions .
The \”0\” between the numbers and the \”0\” at the end are all valid numbers, while all the \”0\”s in front of the numbers only serve as positioning. A positive integer ending in \”0\” with an undefined number of significant digits.
First, measure the composition of the substance. The method for completing this task is called qualitative analysis;
Then, the relative percentages of these components are determined. The method for completing this task is called quantitative analysis;
From this, it can be seen that analytical chemistry is composed of It consists of two parts: qualitative analysis and quantitative analysis.
In general analysis, qualitative analysis must precede quantitative analysis.
62. What are the categories of chemical analysis methods according to different operating methods?
Gravimetric analysis, titration analysis, gas analysis
Optical analysis, electrolysis. There are four types of chemical analysis, chromatography and mass spectrometry
64. The reaction of complex titration must meet the following conditions?
(1) The generated complex must have a definite composition, that is, the central ion and the complexing agent must be combined strictly in a certain proportion;
(2) The generated complex must have sufficient stability;
(4) There should be an appropriate indicator for reaching the theoretical end point of the reaction Or other methods.
65. A precipitation reaction suitable for titration must meet the following requirements?
(1) The reaction speed is fast and the solubility of the precipitate formed is small;
(2) The reaction is carried out quantitatively according to a certain chemical formula;
66. The analysis results should make the following judgments on suspicious values
(1) During the analysis and experiment process, have If you know that a certain measurement value is caused by errors in operation, you should discard the data immediately;
(2) If you cannot find the reason for the suspicious value , should not be discarded or retained at will, but should be selected according to the \”4 times average deviation method\” or Q test method
67. The selection of buffer solutions should be considered. The following principles?
(1) The buffer solution does not interfere with the analytical experimental process;
( 3) The pK acid value or pK base value of the buffer solution should be close to the pH value that needs to be controlled.
It is divided into national standards, industry standards, and local standards. and four major categories of enterprise standards.
69. Is the standard method the state-of-the-art method?
The standard method is not necessarily the most technically advanced and accurate method, but it is simple and easy to implement under certain conditions, and has a certain degree of reliability and reliability. The development of economical and practical mature methods and standard methods always lags behind actual needs. Standardization organizations revise existing standards and promulgate some new standards every few years.
(1) Use a ballpoint pen or pen to record in the notebook during the experiment, and should not copy it into the notebook afterwards; (Pharmaceutical Research Corrigendum: Pharmaceutical Research and Development Field A signature pen or pen should be used)
(2) The measurement conditions, instruments, reagents, data and operators must be recorded in detail, clearly and truly;
(3) Data using legal measurement units should be recorded according to the effective reading digits of the measuring instrument, and any observation errors should be noted;
(4) To change the incorrectly remembered data, draw a horizontal line on the original data to indicate erasure, and write corrected data next to it.
The entire thickness of the skin is lost, including: subcutaneous tissue, muscles, and bones. The wound surface is gray-white or burnt yellow, without blisters and pain, and the sensation disappears.
It can be gently bandaged with sterile gauze to prevent infection and shock, keep the injured warm and supply oxygen, and send the injured to the hospital for emergency treatment in time.
Usually called the \”rounding to five to make even\” rule, rounding to five is considered, that is, when the mantissa is ≤ 4, it is rounded, and the mantissa is Carry at 6. When the mantissa is exactly 5, it should be considered whether the remaining digits are odd or even. If the number before 5 is an even number, the 5 should be discarded. If the number before 5 is an odd number, the 5 should be carried.
(1) The power supply voltage should be consistent with the voltage specified by the electric furnace itself;
(2 ) If the heating container is made of metal, an asbestos mesh should be placed on it to prevent the metal container from touching the electric furnace wire, causing short circuit and electric shock accidents;
(3) Refractory bricks The grooves of the stove plate should be kept clean at all times, and burnt residue should be removed promptly (the power must be turned off during removal) to keep the furnace wire conductive well;
(4) The continuous use time of the electric furnace should not be too long. If it is too long, the use of the furnace wire will be shortened.life.
74. How many methods are there for drying glass instruments? What are each?
Answer: There are three types, air drying, tumble drying, and hot or cold air drying.
75. Why are quartz cuvettes used in TBC measurements?
Because TBC is measured at 485nm, near ultraviolet light region, and quartz glass can transmit ultraviolet light, so a quartz cuvette is used.
76. How many methods are there for sample dissolution? What are each?
Sense refers to the mass value required for the balance position of the balance to produce a division change on the signboard, in milligrams/division.
The reduction method reduces the chance of the substance being weighed coming into contact with air, so it is suitable for weighing substances that easily absorb water, oxidize or react with carbon dioxide. Several copies of the same sample.
79. What are the effects of temperature, humidity and vibration on the balance?
The temperature of the balance room should be maintained between 18 and 26°C, and the temperature fluctuation should not be greater than 0.5°C/h. If the temperature is too low, the operator\’s body temperature and light source lamp Heat has a great influence on the balance, causing zero point drift. The relative humidity in the balance room should be maintained at 55 to 75%, preferably 65 to 75%. If the humidity is too high, for example, above 80%, the adsorption phenomenon of balance parts, especially agate parts, will be obvious, causing the balance to swing slowly, perishable metal parts, and optical mirrors prone to mildew. When the humidity is lower than 45%, the material is easily charged with static electricity, making the weighing inaccurate. The balance cannot be subject to vibration. Vibration can cause the balance\’s stopping point to change, and it is easy to damage the balance\’s knife and blade pad.
80. If there is a problem with the weighing quality, how many aspects should we look for?
The reasons should be found from four aspects, including the object to be weighed, the balance and weights, and the weighing operation.
Usually includes several links such as sampling, weighing samples, sample decomposition, selection of analysis methods, separation of interfering impurities, analysis and measurement, and calculation of results.
82. What are the three instruments used in titration analysis to accurately measure the volume of a solution?
83. What is the method for oiling an acid buret?
Remove the piston, dry the inner wall of the piston and plug sleeve with clean paper or cloth, dip a small amount of Vaseline with your fingers and apply a thin layer of Vaseline on both ends of the piston Do not apply Vaseline on both sides of the piston hole to avoid blocking the piston hole. After coating, put the piston back into the sleeve, rotate the piston in the same direction several times to make the Vaseline evenly distributed and transparent, and then cover it with a rubber ring. , fix the piston in the plug sleeve to prevent it from sliding out.
It is a quantitative analysis method that determines the content of the component to be determined based on the weight of the reaction product.
It is a solution with a certain pH value composed of a weak acid and its salts or a weak base and its salts. When the amount of acid or alkali is added, the pH value of the solution No significant changes occur.
Answer: It is a method that uses the reaction between acids and bases to determine the content of substances, also called the neutralization method.
Answer: It refers to the reagent that indicates the end point of titration in volumetric analysis.
It is the embodiment of a mass unit. It has a certain mass and a certain shape. It is used to measure the mass of other objects and to calibrate balances.
During the titration process, when the dropped standard solution reacts quantitatively with the substance to be measured according to the instructor relationship shown in the chemical reaction formula, this happens when the reaction is complete. One point is called the theoretical end point.
In the titration process, after adding the indicator, the observed transition point when the reaction is complete and produces external effects.
A uniform and stable system composed of molecules, atoms or ions dispersed in another substance is called a solution. The solution is composed of solute and solvent .
That is, at a certain temperature, the number of grams of a certain substance dissolved when it reaches a dissolution equilibrium state in 100g of solvent.
Systematic error is also called measurable error. It is caused by some common reasons in the analysis process. When measurements are repeated, it will show up repeatedly. The impact of the analysis results is relatively fixed.
Accidental error is also called unmeasured error, or random error. It is caused by unfixed (accidental) reasons during the analysis process.
Precision refers to the degree to which the results of several repeated measurements are consistent with each other under the same conditions.
The percentage or thousandth of the standard deviation in the average value is called the relative standard deviation.
The standard addition method is to add different amounts of standard solutions to several sample solutions, then measure the absorbance according to the steps of drawing a standard curve, and draw the absorbance – Add the concentration curve and use extrapolation to find the concentration of the sample solution.
There are a few questions below for everyone to practice.
100. According to the standards of the Ministry of Chemical Industry of my country, the color of the reference reagent is marked (D)
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2. DingTalk online course process and precautions
DingTalk Dingwang classes are a form of online education. Especially during the epidemic prevention and control period, they have become a common distance learning method. The process mainly includes the following steps: First, the teacher opens the DingTalk application and creates a live meeting or ordinary meeting in the \”Conference\” module. Next, send the invitation code to the student or student\’s parent to allow them to join the meeting. Before the meeting begins, teachers can conduct equipment and network tests to ensure the smoothness and stability of the live broadcast. With further development, teachers can share documents or screens and use tools such as DingTalk Business School to support teaching. Teachers can review after the meeting to examine student progress.
1. Teachers should keep confidentiality when creating meetings and not disclose the invitation code to unauthorized persons.
2. It is recommended that teachers consider students’ network conditions and choose the most appropriate live broadcast resolution to avoid lagging.
3. During the live broadcast, teachers should maintain communication and interaction with students and guide students to actively participate in the course.
4. Before ending the meeting, teachers should reconfirm students’ participation, especially important criticism and guidance for absent students.
3. What should you pay attention to when collecting waste?
When collecting waste, you should pay attention to the classification of waste. You can also classify it according to reusable waste and non-reusable waste. Separate environmental waste and non-environmental waste, place all kinds of waste in an orderly manner, and send them to the waste collection station. At the same time, pay attention to the reasonable price of the waste and the accurate weight to avoid unnecessary trouble. You must have a good attitude. Keep in mind that harmony brings wealth!
Okay, this is the end of the article, I hope it can help everyone.
