**Title: Basic Training for Laboratory Technicians

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Basic knowledge training for laboratory technicians 1. What is the method for oiling an acid buret? Answer: Remove the piston, dry the inner wall of the piston and plug sleeve with a clean paper or cloth, dip a small amount of Vaseline with your finger and apply a thin circle 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 and rotate the piston in the same direction several times to make the Vaseline evenly distributed and transparent. Then cover it with a rubber ring to fix the piston in the sleeve to prevent it from slipping out. 2. How to test for leakage in an acid burette? Answer: Close the piston, fill in distilled water to a certain score line, stand the burette upright for about 2 minutes, carefully observe whether the liquid level on the score line drops, whether there are 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, wipe it dry and re-oil it. 3. How to test for leaks in an alkaline burette? Answer: Fill the distilled water to a certain score line, stand the burette upright for about 2 minutes, carefully observe whether the liquid level on the score line drops, or whether there are water drops dripping from the lower end of the burette. If there is water leakage, 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, they may leak, and if they are too large, it will be inconvenient to operate. 4. How to fill an acid burette with a solution? Answer: 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 residual moisture in the burette and ensure that the concentration of the standard solution remains unchanged, the burette should be rinsed with this standard solution 2-3 times, each time using about 10mL, and a small amount (about 1/3) should be released from the lower opening. To wash the tip part, you should close the piston, hold the burette horizontally and rotate it slowly so that the solution is in contact with the inner wall of the tube. Finally, pour the solution out of the tube mouth and discard it, but do not open the piston to prevent the grease on the piston from rushing into the tube. Wash it a second time after emptying it as much as possible, and rinse the tip part every time. After washing 2-3 times, you can load the standard solution to above the "0" mark. 5. How to catch bubbles in an alkaline burette? Answer: For an alkaline burette, you should bend the hose upwards and squeeze the glass beads hard to make the solution spray out from the tip to eliminate air bubbles. The bubbles in an alkaline burette are usually hidden near the glass beads. You must check with the light whether the bubbles in the hose are completely gone. After they are gone, adjust the liquid level to 0.00mL, or write down the initial reading. 6. What is the correct method for titration? Answer: During titration, the tip of the burette should be inserted 1-2cm below the mouth of the conical flask (or the mouth of the beaker). The titration speed should not be too fast, 3-4 drops per second is appropriate. It must not flow down into a liquid column and shake while dropping. Make a circular rotation in the same direction and do not vibrate back and forth, because the solution will splash out. When approaching the end point, add 1 drop or half a drop, and blow a small amount with a washing bottle to rinse the inner wall of the conical flask. Let all the attached solution flow down, then shake the Erlenmeyer flask and observe whether the end point has been reached. If the end point has not been reached, continue the titration until the end point is accurately reached. 7. Buret readings should comply with the following rules? Answer: (1) After injecting or releasing the solution, you need to wait 30s-1min before reading (2) The burette should be clamped vertically on the titration table for reading or use two fingers to hold the upper end of the burette so that it is vertical and then read (3) For colorless solutions 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 aligned with the highest points on both sides of the liquid surface. The same standard should be used for the first and final readings. 8. Precautions for using burettes? Answer: (1) After using the burette, 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 the next use. (2) When the acid burette is not used for a long time, the piston part should be padded with paper. Otherwise, the stopper will not be easy to open over time. When the alkaline burette is not in use, the hose should be unplugged and dipped in some talcum powder to preserve it. 9. How to wash pipettes and pipettes? Answer: Both pipettes and pipettes can be washed with tap water, and then washed with distilled water. When they are dirty (when water beads are hanging on the inner wall), they can be washed with chromic acid washing solution. 10. What is the method for washing pipettes or pipettes with washing liquid? Answer: Hold the pipette or pipette in your right hand, insert the lower opening of the tube into the lotion, 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 top of the pipette or pipette. Slowly release the fingers of your left hand and slowly suck the lotion into the tube until it rises to the part above the mark. After waiting for a while, put the lotion back into the original bottle. 11. How to draw the solution with a pipette? Answer: Use the thumb and middle finger of your right hand to hold the upper end of the pipette or pipette, and insert the lower opening of the pipe into the solution to be obtained. Do not insert it too shallowly or too deeply. Too shallow will cause a suction, and the solution will be sucked into the ear cleaning bulb and the solution will be dirty. If it is too deep, too much solution will stick to the outside of the tube. 12. What should I pay attention to when using pipettes and burettes? Answer: (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 uppermost surface of the scale as the starting point and release the required volume downwards each time, instead of absorbing the volume as much as the volume is released. 13. How to test volumetric flasks for leaks? Answer: Before use, you should first check whether the stopper of the volumetric flask is tight. To do this, you can fill the bottle with tap water close to the mark, cover the stopper, hold the stopper with your hand, and turn the volumetric flask upside down to see if there is water leaking from the mouth of the bottle. If there is no leakage, stand the bottle upright, turn the stopper about 180°, and then invert it again. In order to prevent the stopper from being lost and messy, plastic strings are often used to tie it to the neck of the bottle. 14. Precautions for using volumetric flasks? Answer: (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) When the volumetric flask is not used for a long time, it should be washed and the stopper should be padded with paper to prevent the stopper from being opened after a long time. 15. What types of chemical reagents are classified according to their uses? Answer: It is divided into the following categories, general reagents, reference reagents, organic reagents for inorganic ion analysis, chromatographic reagents and preparations, indicators and test papers, etc. 16. What conditions should be met as a reference material? Answer: (1) High purity, above 99.9% (2) Completely consistent composition and chemical formula (3) Good stability, It is not easy to absorb water and is 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 of expressing the concentration of general solutions? Answer: mass percentage concentration, volume percentage concentration, mass volume percentage concentration. 18. Briefly describe what two changes occur in a substance during the dissolution process? Answer: One is that solute molecules (or ions) overcome their mutual attraction to diffuse between water molecules, which is a physical change. 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. What will happen to solutions that are regularly stored in glass bottles? Answer: It will cause the solution to contain sodium, calcium, and silicate impurities or cause some ions in the solution to adsorb to the glass surface, reducing the concentration of the ions in the solution. 20. How to open a volatile reagent bottle in summer? Answer: First, do not point the bottle mouth towards your face, and then soak the bottle in cold water for a period of time to avoid the danger of gas-liquid impact in the bottle due to high room temperature. After taking out the reagent, close the stopper tightly, and bottles that release toxic or odorous gases should be sealed with wax. 21. What are the methods to improve the accuracy of analysis? Answer: Choose an appropriate analysis method, increase the number of parallel measurements, and eliminate systematic errors in the measurement. 22. What are the characteristics of accidental errors and how to eliminate them? Answer: Characteristics: Under certain conditions, the absolute value of the error in a limited number of measured values will not exceed a certain limit. Positive and negative accidental errors of the same size have almost 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. On the premise of eliminating systematic errors, the average value may be close to the true value. 23. What are the characteristics of systematic errors and how to eliminate them? Answer: Reasons: A. Instrument error; B. Method error; C. Reagent error; D. Operational error. Methods to eliminate these errors: Conduct blank tests, calibrate the instrument, and perform control tests. 24. What is the relationship between accuracy and precision? Answer: To achieve high accuracy, precision must also be high first. However, high precision does not necessarily mean high accuracy, as there may be systematic errors in the measurements. In other words, precision is a prerequisite for ensuring accuracy. 25. Systematic error? Answer: Systematic error, also known as measurable error, is caused by certain constant factors in the analysis process. It reappears in repeated measurements and has a relatively fixed impact on the analysis results. 26. Why must a new glass electrode be soaked for more than 24 hours? Answer: Only by soaking the glass membrane in water, allowing it to swell and form a hydrated layer on its surface, can it maintain sensitivity to H+ ions. This is done to reduce the asymmetrical potential and achieve stability. 27. How can the absorbance values of standard solutions and test solutions be kept between 0.05–1.0 during colorimetric analysis? Answer: (1) Adjust the solution concentration; when the concentration of the component being measured is high, less sample can be used, or the solution can be diluted to keep the absorbance within 0.05–1.0. (2) Use cuvettes of different thicknesses. Since absorbance A is proportional to the thickness of the cuvette, increasing the thickness will also increase the absorbance value. (3) Select a blank solution. If the reagents used for color development are colorless and there are no other colored ions in the test solution, distilled water can be used as the blank. If the reagent itself has color, then distilled water containing that reagent should be used as the blank. If the reagent is colorless but there are other colored ions in the test solution, then the test solution without the reagent should be used as the blank. 28. Why must a new glass electrode be soaked for more than 24 hours? Answer: Only by soaking the glass membrane in water, allowing it to swell and form a hydrated layer on its surface, can it maintain sensitivity to H+ ions. This is done to reduce the asymmetrical potential and achieve stability. 29. How can the absorbance values of standard solutions and test solutions be kept between 0.05–1.0 during colorimetric analysis? Answer: (1) Adjust the solution concentration; when the concentration of the component being measured is high, less sample can be used, or the solution can be diluted to keep the absorbance within 0.05–1.0. (2) Use cuvettes of different thicknesses. Since absorbance A is proportional to the thickness of the cuvette, increasing the thickness will also increase the absorbance value. (3) Select a blank solution. If the reagents used for color development are colorless and there are no other colored ions in the test solution, distilled water can be used as the blank. If the reagent itself has color, then distilled water containing that reagent should be used as the blank. If the reagent is colorless but there are other colored ions in the test solution, then the test solution without the reagent should be used as the blank. 30. What is the standard addition method? Answer: The standard addition method involves adding varying amounts of standard solution to several sample solutions, then measuring the absorbance following the steps used to create a standard curve. An absorbance-concentration curve is drawn, and the concentration of the sample solution is determined through extrapolation. 31. What conditions are necessary for titrimetric analysis? Answer: There are three main conditions: (1) An analytical balance for accurately weighing substances and containers for measuring solution volumes; (2) A standard solution suitable for titration; (3) An indicator that can accurately determine the theoretical endpoint. 32. What are the categories of titrimetric analysis? Answer: There are four categories: acid-base titration, complexometric titration, redox titration, and precipitation titration. 33. What conditions are necessary for titrimetric analysis? Answer: There are three main conditions: (1) An analytical balance for accurately weighing substances and containers for measuring solution volumes; (2) A standard solution suitable for titration; (3) An indicator that can accurately determine the theoretical endpoint. 34. What are the categories of titrimetric analysis? Answer: There are four categories: acid-base titration, complexometric titration, redox titration, and precipitation titration. 35. What is routine analysis? Answer: Routine analysis refers to the daily analyses carried out in laboratories to support production processes. It is also known as conventional analysis. To ensure smooth production, it’s necessary to obtain analysis results quickly. Such routine analysis is also called rapid analysis or in-process analysis. 36. What is arbitration analysis? Answer: When there are disputes over analysis results among different units, those units are required to conduct accurate analyses using specified methods in order to determine the reliability of the original results. This type of analysis is called arbitration analysis. 37. What are the main differences between photoelectric colorimetry and spectrophotometry? Answer: The main difference lies in the way monochromatic light is obtained. A photoelectric colorimeter uses filters to separate light, while a spectrophotometer uses prisms or gratings. Prisms or gratings disperse the incident light into spectral bands, thereby producing monochromatic light with higher purity and a narrower wavelength range. 38. What is the working principle of spectrophotometry? Answer: The basic principle of spectrophotometry is to use a prism or grating to convert mixed light into monochromatic light. This monochromatic light is then passed through the colored solution being analyzed, and the resulting electrical signal is detected by a photodetector. The absorbance and transmittance are then displayed on a measuring instrument. 39. What are complementary colors? Answer: The method of measuring the intensity of light that passes through a colored solution using the photoelectric effect to determine the concentration of the substance being analyzed is called photoelectric colorimetry. 40. What are the five main components of photoelectric colorimetry? Answer: Light source, filter, cuvette, photodiode, and galvanometer. 41. How is a standard curve for determining the concentration of a substance using spectrophotometry created? Answer: First, prepare a series of standard solutions with different concentrations (5–10 solutions). Measure their absorbance A (or transmittance T%) at the wavelength at which maximum absorption occurs. Then, plot these values on graph paper, with solution concentration on the x-axis and absorbance on the y-axis. If the absorption of light by the substance follows the law of light absorption, a straight line passing through the origin will be obtained, which constitutes the standard curve. 42. How can the absorbance values of standard solutions and test solutions be kept between 0.05–1.0 during colorimetric analysis? Answer: (1) Adjust the solution concentration; when the concentration of the component being measured is high, less sample can be used, or the solution can be diluted to keep the absorbance within 0.05–1.0. (2) Use cuvettes of different thicknesses. Since absorbance A is proportional to the thickness of the cuvette, increasing the thickness will also increase the absorbance value. (3) Select a blank solution. If the reagents used for color development are colorless and there are no other colored ions in the test solution, distilled water can be used as the blank. If the reagent itself has color, then distilled water containing that reagent should be used as the blank. If the reagent is colorless but there are other colored ions in the test solution, then the test solution without the reagent should be used as the blank. 43. What properties does glass have, and what are its main chemical components? Answer: Glass has high chemical and thermal stability, good transparency, certain mechanical strength, and excellent insulating properties. Its chemical composition mainly consists of SiO2, CaO, Na2O, K2O. 44. What is the method for cleaning glass filter elements with sand cores? Answer: (1) Before using a new filter, it should be cleaned by suction filtration using hot hydrochloric acid or chromic acid solution, followed by rinsing with distilled water. It can be washed repeatedly with water either in an upright or inverted position. (2) Appropriate detergents should be used to dissolve any precipitates present, or the precipitates can be washed with water in an inverted position before being rinsed thoroughly with distilled water. They should then be dried at 110°C and stored in a dust-free cabinet or covered container; otherwise, accumulated dust and precipitates can clog the filter pores and make them difficult to clean. 45. How should instruments with ground glass stoppers be stored? Answer: For volumetric flasks or colorimetric tubes, it’s best to secure the stopper and the opening of the tube using small ropes or plastic tubes before cleaning, to prevent the stopper from breaking or getting mixed up with other items. For instruments with ground glass stoppers that need to be stored for a long time, a piece of paper should be placed between the stoppers to prevent them from sticking together over time. Titration tubes that will not be used for a long time should have the vaseline removed, a piece of paper placed inside them, and the piston secured with a rubber band. If there are sand particles between the ground glass stoppers, do not turn them forcefully to avoid damaging their precision. Similarly, do not use cleaning powder to scrub the ground glass surfaces. 46. Why is sampling important? Answer: Generally speaking, sampling errors are often greater than analysis errors. Therefore, it’s important to understand some basic principles of sampling and sample preparation. If the sampling and sample preparation methods are incorrect, even if the analysis is carried out very carefully and accurately, it will be pointless. In some cases, this can even lead to negative consequences for production and research. 47. What is the maximum weighing capacity of a balance? Answer: The maximum weighing capacity, also known as the maximum load, refers to the highest weight that a balance can measure. This capacity must be greater than the possible mass of the object being weighed. 48. What are the precautions for sampling chemical products? Answer: For chemical products with a relatively uniform composition, any portion of them can be taken as a sample for analysis. When dealing with large quantities, a sampling percentage should be determined, and portions of the material should be taken and mixed together to form the analysis sample. 49. What are the general requirements for decomposing samples? Answer: (1) The sample should be completely decomposed, and the resulting solution should not contain any fine particles or powders from the original sample. (2) During the decomposition process, no loss of the components being analyzed should occur due to volatilization. (3) The decomposition process should not introduce any components that could interfere with the analysis. 50. What are the types of titration tubes? Answer: Based on their volume, they can be classified as constant-volume, semi-micro, and micro titration tubes. Based on their structure, they can also be divided into ordinary titration tubes and automatic titration tubes. 51. How do pipettes or suction pipets adjust the liquid level? Answer: Lift the pipette or burette upward away from the liquid surface, keeping the tip against the inner wall of the container holding the solution; keep the tube upright. Slightly relax your index finger to allow the solution in the tube to flow out slowly from the bottom, until the bottom of the meniscus is in contact with the marking. Then press the tip of the tube tightly with your index finger to remove any droplets on it, take the pipette or burette away, and insert it into the container designed to hold the solution. 52. How to release the solution from a pipette or syringe? Answer: If the container for holding the solution is a conical flask, the flask should be tilted while the pipette or burette remains upright, with its lower end pressed against the inner wall of the flask. Release the index finger to allow the solution to flow down along the wall of the flask. After the flow has stopped, wait about 15 seconds with the tip of the tube in contact with the inner wall of the bottle, and then remove the pipette or syringe. The small amount of solution remaining at the tip of the tube should not be forced out using external force, as the volume of solution retained at the tip has already been taken into account when calibrating the pipette or pipettor. 53. How to transfer a solution into a volumetric flask? Answer: During the transfer process, insert a glass rod into the volumetric flask; position the spout of the beaker close to the glass rod so that the solution flows in slowly along it. The lower end of the glass rod should be close to the inner wall of the flask neck, but not too close to the opening, to prevent the solution from spilling over. Once the solution has stopped flowing, lift the beaker slightly upward using a glass rod while keeping it upright, so that the drop of solution remaining on the mouth of the beaker flows back into it. It can be washed 3–4 times with a small amount of distilled water; the washings should be transferred to the volumetric flask in the same manner as described above. 54. How to dilute a solution using a volumetric flask? Answer: After transferring the solution into the volumetric flask, add distilled water to dilute it to about 3/4 of its volume. Then shake the volumetric flask gently several times to achieve a preliminary mixing; this also helps to prevent any change in volume after mixing. Then continue adding distilled water, adding it drop by drop carefully as you approach the mark, until the meniscus of the solution is tangent to the mark, after which seal the stopper tightly. 55. How to mix a volumetric flask thoroughly? Answer: Press the stopper with the index finger of the left hand, and use the tip of the right finger to press against the edge of the bottom of the bottle. Invert the volumetric flask and shake it, then invert it again to allow the bubbles to rise to the top. Repeat this process 15–20 times to achieve mixing. 56. What is the method for calibrating a volumetric flask? Answer: Weigh a certain volume of water, and then convert the mass of water into a volume based on the density of water at that temperature. 57. The burette is clogged with grease; how to deal with it? Answer: If the piston hole is blocked by old oil residue, it can be gently removed using a thin metal wire. If the tip of the tube is clogged with grease, fill the entire tube with water first, then place the tip in hot water to melt the grease, and finally open the piston suddenly to flush it away. 58. What are the precautions for using chemical reagents? (1) One should be familiar with the properties of the most commonly used reagents. (2) Care should be taken to protect the labels on the reagent bottles. (3) To prevent the reagents from getting contaminated, they should be removed from the bottles using clean hornspoons; the reagents taken out must not be poured back into the original bottles. (4) It is not allowed to inhale deeply through the nose near the mouth of the reagent bottle, and it is absolutely forbidden to taste the reagents with the tongue. 59. What are the precautions for preparing solutions? Answer: (1) The solutions used in analytical experiments should be prepared using pure water, and the containers used should be washed with pure water at least three times. (2) Solutions should be stored in reagent bottles with lids. (3) Each reagent bottle must have a label indicating its name, specifications, concentration, and date of preparation. (4) When storing solutions, care should be taken to prevent the solutions from deteriorating. (5) When preparing solutions of sulfuric acid, phosphoric acid, nitric acid, hydrochloric acid, etc., the acid should be poured into water. (6) Corrosive and highly toxic solutions should not be touched with bare hands; highly toxic waste liquids must be detoxified before being discharged directly into the sewer system. (7) One should be familiar with the methods for preparing common solutions. 60. What is the meaning of “0” in significant figures? Answer: The “0”s between digits as well as the “0” at the end are all significant figures, while all “0”s before a digit serve only to indicate position. For positive integers ending in “0”, the number of significant figures is uncertain. 61. Into which two steps is analytical work divided? Answer: First, the composition of a substance is determined; the method used for this purpose is called qualitative analysis. Then, the relative percentage content of these components is determined; the method used for this purpose is called quantitative analysis. Thus, analytical chemistry consists of qualitative analysis and quantitative analysis. In general analyses, qualitative analysis precedes quantitative analysis. 62. Into which categories are chemical analysis methods classified based on their operational methods? Answer: They are divided into gravimetric analysis, titrimetric analysis, and gas analysis. 63. Into which categories are instrumental analysis methods divided? Answer: They are divided into optical analysis, electrochemical analysis, chromatographic analysis, and mass spectrometric analysis. 64. What conditions must be met for a complexation titration reaction to take place? Answer: (1) The resulting complex must have a definite composition, that is, the central ion and the ligand must combine in a precise ratio; (2) The resulting complex must be sufficiently stable; (3) The rate of the complexation reaction must be fast enough; (4) There must be an indicator or other method to determine the theoretical endpoint of the reaction. 65. What requirements must a precipitation reaction suitable for use in titrations meet? Answer: (1) The reaction must be fast, and the precipitate formed must have low solubility; (2) The reaction must proceed quantitatively according to a specific chemical formula; (3) There must be a reliable method to determine the theoretical endpoint. 66. How should suspicious values in analytical results be handled? Answer: (1) If it is known during the analysis that a certain measurement value is due to an error in the procedure, that data should be discarded immediately. (2) If the cause of the suspicious value cannot be identified, it should not be discarded or retained arbitrarily; instead, the “4-fold mean deviation method” or the Q-test method should be used to decide whether to keep or discard it. 67. What principles should be considered when selecting a buffer solution? Answer: (1) The buffer solution should not interfere with the analytical process; (2) The buffer solution should have sufficient buffering capacity; (3) The pK value of the acid or base that makes up the buffer solution should be close to the pH value that needs to be controlled. 68. Into which categories are standards in China divided? Answer: They are divided into national standards, industry standards, local standards, and enterprise standards. 69. Are standard methods the most advanced ones? Answer: Standard methods are not necessarily the technically most advanced or most accurate ones; rather, they are mature methods that are simple to use under certain conditions, and possess a certain level of reliability as well as being cost-effective. The development of standard methods always lags behind actual needs, and standardization organizations revise existing standards every few years and issue new ones. 70. Requirements for original records? Answer: (1) Use a ballpoint pen or fountain pen to record notes in the notebook during the experiment; do not write them down later. (2) Record in detail, clearly, and accurately the measurement conditions, instruments, reagents, data, and the operator. (3) When using legal units of measurement, record data according to the number of significant digits indicated by the measuring instrument. Any observational errors should be noted. (4) To correct incorrect data, draw a horizontal line through the original data to indicate it has been erased, then write the corrected value beside it.
71. What are the symptoms and treatment methods for third-degree burns?
Answer: The entire layer of skin is damaged, including subcutaneous tissue, muscles, and bones. The wound appears grayish-white or charred yellow; there are no blisters, little pain, and loss of sensation. Treatment: Gently bandage the wound with sterile gauze to prevent infection and shock. Keep the patient warm and provide oxygen; promptly send them to the hospital for emergency treatment.
72. What are the rules for rounding numbers?
Answer: This is commonly known as the “round down if ≤4, round up if ≥6; for 5, round to the nearest even number” rule. That is, if the last digit is ≤4, round down; if it’s 6, round up. When the last digit is exactly 5, check whether the preceding digit is odd or even: if it’s even, round down; if it’s odd, round up.
73. What precautions should be taken when using an electric furnace?
Answer: (1) The supply voltage must match the voltage specified for the electric furnace. (2) If heating a metal container, place an asbestos mat underneath to prevent the metal from touching the heating wires, which could cause short circuits or electric shocks. (3) Keep the grooves in the refractory brick furnace tray clean; remove any burnt residues promptly (be sure to turn off power before doing so) to ensure good electrical conductivity of the heating wires. (4) Do not operate the furnace continuously for too long, as this will shorten the lifespan of the heating wires.
74. How many methods exist for drying glassware? What are they?
Answer: There are three: air-drying, oven-drying, and drying with hot or cold air.
75. Why are quartz cuvettes used in TBC measurements?
Answer: TBC measurements are conducted at 485 nm, within the near-ultraviolet range; quartz glass transmits ultraviolet light, hence it is chosen for use as a cuvette material.
76. How many methods exist for dissolving samples? What are they?
Answer: Two: dissolution method and fusion method.
77. What is the sensitivity (division value) of a balance?
Answer: Sensitivity refers to the mass required to produce one divisional change on the scale indicator; its unit is milligrams per division.
78. For which types of substances is the subtraction weighing method suitable?
Answer: This method reduces the exposure of the substance to air, so it is ideal for hygroscopic, easily oxidized, or CO₂-reactive substances; it is also useful when weighing multiple portions of the same sample.
79. What effects do temperature, humidity, and vibration have on balances?
Answer: The temperature in the balance room should be maintained between 18–26°C, with fluctuations no greater than 0.5°C/hour. Too low a temperature makes body heat and lamp warmth affect the balance, causing zero-point drift. Relative humidity should stay at 55–75%, ideally 65–75%. Excessively high humidity (>80%) causes adsorption on parts, especially agate components, making the balance sluggish; it also promotes corrosion of metal parts and mold growth on optical surfaces. Low humidity (<45%) induces static charge on materials, leading to inaccurate weighing. Balances must be protected from vibration, as it can alter their equilibrium point and damage knife edges and knife pads.
80. If there is a problem with measured mass, from how many aspects should one look for causes?
Answer: Causes should be examined from four main aspects: the sample itself, the balance and weights, and the weighing procedure.
81. What are the general steps in analyzing substances?
Answer: Typically include sampling, weighing, sample decomposition, selection of analytical method, separation of interfering impurities, analysis and determination, and calculation of results.
82. Which three instruments are used to accurately measure solution volumes in titrimetric analysis?
Answer: Burettes, pipettes, and volumetric flasks.
83. How is oil applied to an acid burette?
Answer: Remove the stopcock; dry both the stopcock and inner wall of the sleeve using clean paper or cloth. Dip a finger in a small amount of vaseline and apply a thin layer around both ends of the stopcock; avoid applying vaseline directly next to the aperture to prevent blockage. After application, reinsert the stopcock and rotate it several times in the same direction so that the vaseline spreads evenly and becomes transparent. Finally, secure it with a rubber band to prevent slipping out.
84. Gravimetric analysis?
Answer: A quantitative analytical method wherein the content of a component is determined based on the weight of a reaction product.
85. Buffer solution?
Answer: A solution containing a weak acid and its salt or a weak base and its salt; it maintains a relatively constant pH despite addition of small amounts of acid or base.
86. True value?
Answer: The actual numerical value existing objectively.
87. Acid-base titration?
Answer: A method for determining substance content via acid-base reactions; also called neutralization titration.
88. Indicator?
Answer: A reagent used in volumetric analysis to signal the endpoint of a titration.
89. Weight?
Answer: An embodiment of a unit of mass; it possesses a defined mass and shape, used for measuring other objects’ masses and calibrating balances.
90. Theoretical endpoint?
Answer: In titration, the point at which the added standard solution reacts quantitatively with the analyte according to the chemical equation, resulting in complete reaction; this is termed the theoretical endpoint.
91. Titration endpoint?
Answer: In titration, after adding an indicator, the point at which a visible change occurs indicating complete reaction; this is termed the titration endpoint.
92. What is a solution?
Answer: A homogeneous and stable system formed when molecules, atoms, or ions disperse uniformly within another substance; composed of solute and solvent.
93. Solubility?
Answer: At a given temperature, the maximum amount of a substance that can dissolve in 100 g of solvent while maintaining equilibrium.
94. Systematic error? Answer: Systematic error, also known as measurable error, is caused by certain constant factors in the analysis process. It reappears in repeated measurements and has a relatively fixed impact on the analysis results. 95. Random error? Answer: Random error, also known as unmeasurable error or stochastic error, is caused by unpredictable (random) factors during the analysis process. 96. Precision? Answer: Precision refers to the degree to which the results of multiple repeated measurements agree with each other under the same conditions. 97. Relative standard deviation? Answer: The percentage or thousandth expressed as a proportion of the mean value is called the relative standard deviation. 98. Briefly describe what the standard addition method is. Answer: In the standard addition method, unequal amounts of standard solution are added to several sample solutions. Then, the absorbance is measured following the steps for preparing a standard curve, and an absorbance-addition concentration curve is drawn. The concentration of the sample solution is determined by extrapolation. 99. Air is a (A) A. gaseous solution, B. dispersed phase, C. gaseous solvent. 100. According to the standards set by China’s Ministry of Chemical Industry, the color code for reference reagents is (D) A. red, B. blue, C. green, D. light green. 101. In analytical chemistry, the symbol Mr, which is commonly used as a unit of measurement, represents (C) A. mass, B. molar mass, C. relative molecular mass, D. relative atomic mass. 102. 1 mole of H and 1 mole of H2 have (A) A. the same amount of substance, B. the same mass, C. the same basic units. 103. For chemical reagents used in complexometric titration, it is preferable to use reagents with a purity of (B) or higher. A. chemically pure, B. analytically pure, C. laboratory-grade reagents. 104. SI is the abbreviation for (B) A. the basic units of the International System of Units, B. the International System of Units, C. legal units of measurement. 105. When preparing standard solutions directly, it is necessary to use (C) A. analytically pure reagents, B. high-purity or ultra-pure reagents, C. reference substances. 106. The number of basic units in 1 mole of any substance is equal to (A) A. the number of 12C atoms in 0.012 kg, B. 0.012 kg of 12C, C. 12 kg of 12C. 107. The reason why the concentration of Na2S2O3 decreases over time is (C) A. absorption of CO2 from the air, B. oxidation of the substance, C. microbial action. This post was last edited by chengjingbao on 2009-4-4 at 16:32