Essential Questions for Lab Technicians: A Compendium

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This post was last edited by Majestic Ultraman. Edited on 2023-4-9 09:32 1. What is the method for greasing an acid burette? 　　Answer: Remove the piston, and use clean paper or cloth to dry the piston as well as the inner walls of the sleeve. Dip your fingers in a small amount of Vaseline and apply a thin layer of it on both ends of the piston; do not apply Vaseline right next to the piston holes, as this could block them. After applying the Vaseline, put the piston back into the sleeve and rotate it several times in the same direction to ensure that the Vaseline is distributed evenly and the area becomes transparent. Then wrap an rubber band around it to keep the piston in place within the sleeve and prevent it from slipping out. 　　2. How to test for leaks in an acid burette? 　　Answer: Close the piston, fill it with distilled water up to a certain mark, hold the burette upright for about 2 minutes, and carefully observe whether the liquid level on the mark drops, whether water droplets fall from the bottom of the burette, and whether water seeps out from the gaps in the piston. Then rotate the piston 180° and wait for 2 minutes before observing again; if there is any leakage, dry it thoroughly and reapply oil. 　　3. How to test for leaks in a burette? 　　Answer: Fill the burette with distilled water up to the marked line, hold it upright for about 2 minutes, and carefully observe whether the liquid level on the mark drops or whether water droplets appear at the tip of the burette. If there is leakage, the glass bead inside the rubber tube should be replaced; choose one that is of appropriate size and smooth in shape before trying again. A glass bead that is too small or not smooth enough can cause leakage, while one that is too large makes operation inconvenient. 　　4. How to fill a acid burette with solution? 　　Answer: Before filling, the standard solution in the bottle should be shaken well to mix any water that has condensed on the inner walls of the bottle into the solution. To remove any residual water from the burette and ensure that the concentration of the standard solution remains constant, the burette should first be rinsed 2–3 times with this standard solution, using about 10 mL each time. A small amount (about 1/3) of the solution should be poured out from the bottom of the burette to clean the tip portion. The piston should be closed while holding the burette, and it should be rotated slowly so that the solution comes into contact with every part of the inner wall of the tube. Finally, the solution should be poured out from the mouth of the burette and discarded; however, the piston must not be opened to prevent grease from the piston from entering the tube. Try to empty it as much as possible before rinsing it a second time; rinse the tip portion each time. After rinsing 2–3 times in this way, it can be filled with standard solution up to above the “0” mark. 　　5. How to remove bubbles from a burette? 　　Answer: For a burette of the basic type, the rubber tube should be bent upward, and the glass bulb should be squeezed firmly to force the solution to emerge from the tip, thereby removing bubbles. In an alkaline burette, bubbles are usually found near the glass beads; it is necessary to check under light to ensure that all bubbles in the tubing have been removed. After that, adjust the liquid level to 0.00 mL, or record the initial reading. 　　6. What is the correct method for titration? 　　Answer: During titration, the tip of the burette should be inserted 1–2 cm below the mouth of the conical flask (or beaker). The titration rate should not be too fast; 3–4 drops per second is an appropriate speed. The liquid must not flow down in a column, and the flask should be shaken while titrating. It should rotate in a circular motion in the same direction without vibrating back and forth, as that would cause the solution to splash out. Near the endpoint, it should be added in drops or half-drops, and a small amount should be blown into the inner wall of the conical flask using a washing bulb to ensure that all the adhering solution flows down; thereafter, the conical flask is shaken to check whether the endpoint has been reached. If the endpoint has not been reached, continue titrating until the endpoint is accurately attained. 　　7. What rules should be followed when reading a burette? 　　Answer: (1) After adding or removing the solution, wait for 30 seconds to 1 minute before taking a reading. (2) The burette should be held vertically on the titration stand for reading, or its upper end should be held with two fingers to keep it vertical while taking the reading. (3) For colorless or light-colored solutions, the actual lowest point below the meniscus should be read; for colored solutions, the line of sight should pass through the highest points on both sides of the liquid surface. The same standard should be used for the initial and final readings. 　　8. What are the precautions for using a burette? 　　Answer: (1) After using the burette, pour out the remaining solution in it, wash it with water, fill it with distilled water up to above the mark, and cover its mouth with a large test tube; this way, there is no need to clean it with cleaning solution before using it again. (2) When an acid burette is not in use for an extended period, paper should be placed under the piston; otherwise, over time it will become difficult to open the stopper. When a base burette is not in use, the rubber tube should be removed and stored with some talcum powder. 　　9. How to wash pipettes and volumetric pipettes? 　　Answer: Both pipettes and burettes can be washed with tap water and then rinsed with distilled water; when they are quite dirty (with water droplets remaining on their inner walls), they can be cleaned using chromic acid solution. 　　10. What is the method for cleaning pipettes or pipettes using a cleaning solution? 　　Answer: Hold the pipette or burette in the right hand, inserting the lower end of the tube into the washing solution. Hold the ear bulb in the left hand, first expelling the air from inside the bulb, then attaching the tip of the bulb to the upper end of the pipette or burette. Gently release the fingers of the left hand to allow the washing solution to be slowly drawn into the tube until it reaches above the marked level. After waiting for a moment, pour the washing solution back into its original container. 　　11. How to use a pipette to draw up the solution? 　　Answer: Use the thumb and middle finger of the right hand to hold the upper end of the pipette or syringe, and insert the lower end of the tube into the solution from which you want to draw liquid. Do not insert it too shallowly or too deeply; inserting it too shallowly can cause vacuum to be created, pulling the solution into the bulb and contaminating it, while inserting it too deeply can result in too much solution adhering to the outside of the tube. 　　12. What are the precautions when using pipettes and burettes? 　　Answer: (1) Pipettes and pipettes used in precision analysis are not allowed to be dried in an oven ； (2) Pipettes are often used in conjunction with volumetric flasks; therefore, their relative volumes are typically calibrated before use ； (3) To reduce measurement errors, the pipette should always start from the top scale mark each time and dispense the desired volume downward, rather than drawing up the same volume as was dispensed. 　　13. How to test for leaks in a volumetric flask? 　　Answer: Before use, it is necessary to check whether the stopper of the volumetric flask fits tightly. To do this, fill the flask with tap water up to near the mark, close the stopper, hold it in place with your hand, turn the flask upside down, and check if any water leaks from the mouth of the flask. If there is no leakage, turn the flask back upright, rotate the stopper about 180°, and then try turning it upside down again. To prevent the stopper from getting lost or mixed up, it is common to tie it to the neck of the flask using a plastic string. 　　14. What are the precautions when using a volumetric flask? 　　Answer: (1) In analytical work requiring high precision, volumetric flasks must not be placed in an oven for drying or heating ； (2) Do not store the prepared solution in a volumetric flask for an extended period of time ； (3) When the volumetric flask is not in use for an extended period, it should be cleaned, and the stopper should be padded with paper to prevent it from becoming difficult to open over time. 　　15. How are chemical reagents classified according to their uses? 　　Answer: They are classified into the following categories: general reagents, reference reagents, organic reagents for inorganic ion analysis, chromatography reagents and preparations, indicators and test strips, etc. 　　16. What conditions should a reference substance meet? 　　Answer: (1) High purity, over 99.9%. (2) Composition and chemical formula are exactly consistent. (3) Good stability; it does not absorb water easily nor get oxidized by air. (4) Higher molar mass allows for larger quantities to be weighed, thereby reducing weighing errors. 　　17. What are the various ways to express the concentration of a general solution? 　　Answer: mass percent concentration, volume percent concentration, mass-volume percent concentration. 　　18. Briefly describe the two changes that occur to a substance during the dissolution process 　　Answer: One is the diffusion of solute molecules (or ions) among water molecules, as they overcome the attractive forces between them – this is a physical change. The other is the attraction between solute molecules (or ions) and water molecules, resulting in the formation of hydrated molecules – this is a chemical change. 　　19. What changes occur to solutions that are stored in glass bottles over a long period of time? 　　Answer: It will cause sodium, calcium, and silicate impurities to be present in the solution, or it may cause certain ions in the solution to adsorb onto the glass surface, thereby reducing the concentration of those ions in the solution. 　　20. How should volatile reagent bottles be opened in summer, and what are the proper procedures? 　　Answer: First, do not point the bottle opening at your face. Next, immerse the bottle in cold water for a while to prevent danger caused by the impact of gas and liquid inside the bottle due to high room temperatures. After taking out the reagent, make sure to seal the cap tightly; bottles that contain toxic or odorous gases should also be sealed with wax. 　　21. What are the methods to improve analysis accuracy? 　　Answer: Choose an appropriate analysis method, increase the number of replicate measurements, and eliminate systematic errors in the measurements. 22. What are the characteristics of random errors and how can they be eliminated? 　　Answer: Characteristics: Under certain conditions, the absolute value of the errors in a finite number of measurements does not exceed a certain limit. Random errors of the same magnitude occur with almost equal probability; small errors are more likely to occur, while large errors are less likely to occur. 　　Remedial method: Increase the number of measurements by conducting multiple parallel tests and taking their average. This allows the random errors associated with positive and negative values to cancel each other out; by eliminating systematic errors, the average value can approach the true value. 　　23. What are the characteristics of systematic errors and how can they be eliminated? 　　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 systematic errors may exist in the measurements. It can be said that 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 does a new glass electrode need to be soaked for more than 24 hours? 　　Answer: The glass membrane can maintain its sensitivity to H+ ions only when it is immersed in water, allowing the surface of the membrane to swell and form a hydrated layer; this is necessary to reduce the asymmetric potential and achieve stability. 　　27. How to control the absorbance values of the standard solution and the sample solution to be between 0.05 and 1.0 during colorimetric analysis? 　　Answer: (1) Adjust the solution concentration; when the content of the component being measured is high, a smaller sample weight can be used, or the solution can be diluted to keep its absorbance between 0.05 and 1.0. 　　(2) Use cuvettes of different thicknesses. Since absorbance A is directly proportional to the thickness of the cuvette, increasing the thickness of the cuvette also increases the absorbance value. 　　(3) Choose a blank solution: when both the color-developing agent and other reagents are colorless, and there are no other colored ions in the solution to be analyzed, distilled water can be used as the blank solution. If the color-developing agent itself has color, then distilled water to which the color-developing agent has been added should be used as the blank. If the color developer itself is colorless but there are other colored ions in the solution to be tested, the solution to be tested without the color developer should be used as a blank. 　　28. Why must a new glass electrode be soaked for more than 24 hours? 　　Answer: The glass membrane can maintain its sensitivity to H+ ions only when it is immersed in water, allowing the surface of the membrane to swell and form a hydrated layer; this is necessary to reduce the asymmetric potential and achieve stability. 　　29. In colorimetric analysis, how can the absorbance values of the standard solution and the sample solution be kept between 0.05 and 1.0? 　　Answer: (1) Adjust the solution concentration; when the content of the component being measured is high, a smaller sample weight can be used, or the solution can be diluted to keep its absorbance between 0.05 and 1.0. 　　(2) Use cuvettes of different thicknesses. Since absorbance A is proportional to the thickness of the cuvette, increasing the thickness of the cuvette also increases the absorbance value. 　　(3) Choose a blank solution: when both the color-developing agent and other reagents are colorless, and there are no other colored ions in the solution to be analyzed, distilled water can be used as the blank solution. If the color-developing agent itself has color, then distilled water to which the color-developing agent has been added should be used as the blank. If the color developer itself is colorless but there are other colored ions in the solution to be tested, the solution to be tested without the color developer should be used as a blank. 　　30. Briefly describe what the standard addition method is 　　Answer: The standard addition method involves adding varying amounts of standard solution to several portions of the sample solution. Then, following the steps for constructing a standard curve, the absorbance is measured. An absorbance-versus-added-concentration curve is plotted, and the concentration of the sample solution is determined by extrapolation. 　　31. What are the necessary conditions for conducting titrimetric analysis? 　　Answer: There are three conditions in total: (1) an analytical balance for accurately weighing the substances and containers for measuring the volume of solutions; (2) a standard solution for carrying out titration; (3) an indicator that can accurately determine the theoretical endpoint. 　　32. What are the classifications of titrimetric analysis? 　　Answer: There are four categories in total: acid-base titration, complexometric titration, redox titration, and precipitation titration. 　　33. What are the necessary conditions for conducting titrimetric analysis? 　　Answer: There are three conditions in total: (1) an analytical balance for accurately weighing the substances and containers for measuring the volume of solutions; (2) a standard solution for carrying out titration; (3) an indicator that can accurately determine the theoretical endpoint. 　　34. What are the classifications of titrimetric analysis? 　　Answer: There are four categories in total: acid-base titration, complexometric titration, redox titration, and precipitation titration. 　　35. Routine analysis? 　　Answer: Routine analysis refers to the daily analyses carried out in standard laboratories in conjunction with production processes; it is also known as conventional analysis. Analytical results need to be provided promptly in order to ensure the smooth progress of production, and this type of routine analysis is called rapid analysis or in-process control analysis. 　　36. Arbitration analysis (also known as adjudication analysis). 　　Answer: When there are disputes over analysis results among different units, the relevant units are required to conduct accurate analyses using specified methods in order to determine the reliability of the original analysis results; this type of analysis is known as an adjudicative analysis. 　　37. Briefly describe the main differences between photoelectric colorimetry and absorbance photometry? 　　Answer: The main difference lies in the method used to obtain monochromatic light. A photometric colorimeter uses filters to separate light, whereas a spectrophotometer uses prisms or gratings for this purpose. Prisms or gratings disperse the incident light into spectral bands, thereby producing monochromatic light of high purity and within a narrow wavelength range. 　　38. Briefly describe the working principle of absorbance spectrophotometry? 　　Answer: The basic principle of absorbance photometry is to use a grating or prism to convert mixed light into monochromatic light, pass this monochromatic light through the colored solution being tested, and then direct it toward a photoelectric detector, which generates an electrical signal; the absorbance and transmittance are then displayed by an indicating instrument. 　　39. What are complementary colors? 　　Answer: The method of using the photoelectric effect to measure the intensity of light that passes through a colored solution, in order to determine the concentration of the substance being analyzed, is called photoelectric colorimetry. 　　40. What are the five main components that make up photoelectric colorimetry? 　　Answer: Light source, filter, cuvette, photocell, galvanometer. 　　41. How to determine the standard curve for measuring the content of a substance by absorbance photometry? 　　Answer: First, prepare a series of (5–10) standard solutions with different concentrations. At the wavelength at which the solution exhibits maximum absorption, measure their absorbance A (or transmittance T%) one by one. Then, on graph paper with a grid, plot the data using the solution concentration as the abscissa and the absorbance as the ordinate. If the absorption of light by the substance being tested conforms to the law of light absorption, a straight line passing through the origin will inevitably be obtained; this is the standard curve. 　　42. How to control the absorbance values of the standard solution and the sample solution to be between 0.05 and 1.0 during colorimetric analysis? 　　Answer: (1) Adjust the solution concentration; when the content of the component being measured is high, a smaller sample weight can be used or the solution can be diluted to keep its absorbance between 0.05 and 1.0. 　　(2) Use cuvettes of different thicknesses. Since absorbance A is proportional to the thickness of the cuvette, increasing the thickness of the cuvette also increases the absorbance value. 　　(3) Choose a blank solution: when both the color-developing agent and other reagents are colorless, and there are no other colored ions in the solution to be analyzed, distilled water can be used as the blank solution. If the color-developing agent itself has color, then distilled water to which the color-developing agent has been added should be used as the blank. If the color developer itself is colorless but there are other colored ions in the solution to be tested, the solution to be tested without the color developer should be used as a blank. 　　43. What are the properties of glass, and what is its main chemical composition? 　　Answer: It has high chemical and thermal stability, excellent transparency, certain mechanical strength, and good insulating properties. Its chemical composition is mainly SiO2, CaO, Na2O, and K2O. 　　44. How to wash a sand-core glass filter? 　　Answer: (1) Before using the 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 in either an upright or inverted position. (2) For different precipitates, use an appropriate detergent to dissolve the precipitate first, or rinse it with water in reverse, then wash it thoroughly with distilled water. Dry it at 110°C, and store it in a dust-free cabinet or a covered container; otherwise, the accumulated dust and precipitates can clog the filter pores and be difficult to clean. 　　45. How should instruments with ground stoppers be stored? 　　Answer: It is best to secure the stoppers and openings of volumetric flasks or colorimetric tubes with small strings or plastic tubes before cleaning, in order to prevent the stoppers from breaking or the tubes from getting mixed up. For ground-glass instruments that are to be stored for a long time, a piece of paper should be placed between the stoppers to avoid sticking over time. For burettes that are not used for a long time, the vaseline should be removed, paper should be placed underneath it, and the piston should be secured with a rubber band for storage. If there are sand particles between the ground glass stoppers, do not turn them forcefully to avoid damaging their precision. Similarly, do not scrub the ground glass joint with cleaning powder. 　　46. What is the importance of sampling? 　　Answer: Generally speaking, sampling error is often greater than analysis error; therefore, it is important to have a basic understanding of sampling and sample preparation. If the sampling and sample preparation methods are incorrect, even the most careful and accurate analysis will be meaningless, and in some cases it can even lead to serious 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 value that a balance can measure. The maximum weighing capacity of a balance 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 selected as the analysis sample. When the batch size is large, a sampling percentage is determined, and portions taken from different areas are 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 powder from the original sample. (2) During the decomposition of the sample, there should be no loss of the components to be analyzed due to volatilization. (3) The decomposition process should not introduce any components that could interfere with the analysis or other unwanted substances. 　　50. What are the types of burettes? 　　Answer: Based on their volume, they are classified into constant-volume, semi-micro, and micro volumetric flasks; whereas based on their structural differences, they can be divided into ordinary volumetric flasks and automatic volumetric flasks, among others. 　　51. How to adjust the liquid level in a pipette or burette? 　　Answer: Lift the pipette or dropper upward away from the liquid surface, keeping the tip against the inner wall of the container holding the solution; maintain a straight position for the tube. Slightly relax your index finger to allow the solution inside 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 dropper away, and insert it into the container designed to hold the solution. 　　52. How to release the solution from a pipette or burette? 　　Answer: If the container for receiving the solution is a conical flask, the flask should be tilted, while the pipette or burette is kept upright with its lower end touching the inner wall of the flask. Then, 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; press the mouth of the beaker tightly against 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’s 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 homogeneity. 　　56. What is the method for calibrating a volumetric flask? 　　Answer: Weigh a certain volume of water, and then convert the mass of the water into a volume based on the density of water at that temperature. 　　57. How to deal with an oil blockage in a burette? 　　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 a clean horn spoon. Do not pour the reagent back into its original bottle. (4) Do not inhale forcefully by putting your nose near the mouth of the reagent bottle, and under no circumstances should you taste the reagent with your tongue. 　　59. What are the precautions when preparing solutions? 　　Answer: (1) The solution used in the analysis experiment should be prepared with pure water, and the containers should be washed with pure water at least three times. (2) The solution should be stored in reagent bottles with caps. (3) Each reagent bottle must have a label indicating its name, specifications, concentration, and date of preparation. (4) When storing the solution, care should be taken to prevent it from deteriorating. (5) When preparing solutions of sulfuric acid, phosphoric acid, nitric acid, hydrochloric acid, etc., the acid should be poured into water. (6) Do not touch corrosive and highly toxic solutions with your hands; highly toxic waste liquids must be detoxified before being discharged directly into the sewer system. (7) One should be familiar with the preparation methods of some common solutions. 　　60. What is the meaning of the “0” in significant figures? 　　Answer: The “0”s between digits and the “0” at the end are all significant figures, while all the “0”s before a digit serve only as placeholders. For positive integers ending in \"0\", the number of significant digits is uncertain. 　　61. Into which two steps is the analysis work divided? 　　Answer: First, the composition of the substance is determined; the method used to accomplish this is called qualitative analysis. Then, the relative percentage content of these components is determined; the method used for this is called quantitative analysis. It can be seen from this that analytical chemistry consists of two main parts: qualitative analysis and quantitative analysis. In general analysis, qualitative analysis must precede quantitative analysis. 　　62. According to different methods of operation, into which categories are chemical analysis methods divided? 　　Answer: There are three methods: gravimetric analysis, titrimetric analysis, and gas analysis. 　　63. Into which categories are instrumental analysis methods divided? 　　Answer: There are four types: optical analysis, electrochemical analysis, chromatographic analysis, and mass spectrometric analysis. 　　64. What conditions must the reaction in complexometric titration meet? 　　Answer: (1) The resulting complex must have a definite composition, that is, the central ion and the ligand combine in a strict ratio; (2) The resulting complex must be sufficiently stable; (3) The rate of the complexation reaction must be fast enough; (4) There must be indicators or other methods to indicate the arrival of an appropriate theoretical endpoint for the reaction. 　　65. What requirements must a precipitation reaction suitable for titration meet? 　　Answer: (1) The reaction proceeds rapidly, and the solubility of the precipitate formed is low; (2) The reaction occurs in a quantitative manner according to specific chemical equations; (3) There are methods to accurately determine the theoretical endpoint. 　　66. How should suspicious values be judged based on the analysis results? 　　Answer: (1) During the analysis of experiments, if it is known that a certain measurement value is caused by an error in the operation, that data should be discarded immediately. (2) If the cause of a suspicious value cannot be identified, it should not be discarded or retained arbitrarily; instead, the \"4-times the mean deviation method\" or the Q-test method should be used to decide whether to keep it or not. 　　67. What principles should be considered when selecting a buffer solution? 　　Answer: (1) The buffer solution does not interfere with the analysis process. (2) The buffer solution has sufficient buffering capacity. (3) The pK acid value or pK base value of the components forming the buffer solution should be close to the pH value that needs to be controlled. 　　68. Into which categories are China’s standards divided? 　　Answer: They are divided into **four categories: standards, industry standards, local standards, and enterprise standards.** 　　69. Is the standard method the most advanced one? 　　Answer: Standard methods are not necessarily the most technologically advanced or accurate ones; rather, they are mature methods that are simple to apply 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 to issue new ones. 　　70. Requirements for original records? 　　Answer: (1) Record in a notebook using a ballpoint pen or pen while conducting the experiment; do not copy the records later. (2) Record the measurement conditions, instruments, reagents, data, and the person performing the operation in a detailed, clear, and accurate manner. (3) Data should be recorded using the legal units of measurement, based on the effective number of digits displayed by the measuring instrument; any observation errors should be indicated. (4) To correct incorrect data, draw a line through the original data to indicate its deletion, and write the corrected data beside it. 　　71. What are the symptoms of third-degree burns and what are the treatment methods? 　　Answer: The entire layer of skin is lost, including the subcutaneous tissue, muscles, and bones; the wound appears grayish-white or burnt yellow, there are no blisters or pain, and sensation is absent. 　　Treatment method: The wound should be gently covered with disinfected gauze to prevent infection and shock; keep the injured person warm and supply them with oxygen, while rushing them to the hospital for emergency treatment. 　　72. What are the rules for digit rounding? 　　Answer: It is commonly referred to as the \"round half to even\" rule. When rounding, if the trailing digit is ≤4, it is dropped; if it is 6, it is rounded up. When the trailing digit is exactly 5, it depends on whether the number of digits remaining is odd or even – if it is even, the 5 is dropped; if it is odd, the 5 is rounded up. 　　73. What are the precautions for using an electric furnace? 　　Answer: (1) The supply voltage should match the voltage specified by the electric furnace itself. (2) If the container being heated is made of metal, an asbestos mesh should be placed under it to prevent the metal container from coming into contact with the furnace wires, thereby avoiding short circuits and electric shock accidents. (3) The grooves in the refractory brick furnace base should be kept clean at all times; burned and charred residues must be removed promptly (power must be turned off during removal) to ensure good electrical conductivity of the furnace filaments. (4) The electric furnace should not be used for extended periods of time, as this will shorten the lifespan of the furnace filaments. 　　74. How many ways are there to dry glass instruments? What are they each? 　　Answer: There are three methods: air drying, drying with heat, and drying with hot or cold air. 　　75. Why are quartz cuvettes used in TBC measurements? 　　Answer: Since TBC measurement is carried out at 485 nm, which is in the near-UV range, and quartz glass can transmit ultraviolet light, quartz cuvettes are used. 　　76. How many methods are there for dissolving samples? What are they each? 　　Answer: There are two methods, the dissolution method and the melting method. 　　77. What is the sensitivity (division value) of a balance? 　　Answer: Sensitivity refers to the mass value required to cause a division change in the balance’s equilibrium position on the scale, measured in milligrams per division. 　　78. Which items are suitable for weighing using the reduction method? 　　Answer: The reduction method reduces the opportunities for the substance being weighed to come into contact with air; therefore, it is suitable for weighing substances that are prone to absorbing moisture, oxidizing, or reacting with carbon dioxide, as well as for weighing multiple samples of the same material. 　　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 temperature fluctuations not exceeding 0.5°C/h. If the temperature is too low, the operator’s body heat as well as the heat from the light source can have a significant impact on the balance, leading to zero-point drift. The relative humidity in the balance room should be maintained at 55–75%, with 65–75% being ideal. When the humidity is too high, above 80%, adsorption occurs significantly on the components of the balance, especially those made of agate, which causes the balance to swing more slowly. Metal components are prone to corrosion, and optical surfaces can develop mold spots. When the humidity is below 45%, the material tends to accumulate static electricity, resulting in inaccurate weighing. The balance must not be exposed to vibrations, as such vibrations can cause changes in the balance’s reading and may also damage the balance’s blades and pads. 　　80. If a problem is found with the measured mass, from which aspects should the causes be sought? 　　Answer: The reasons should be sought from 4 aspects, which are the things being referred to. Look for the causes in aspects such as balances and weights, as well as weighing operations. 　　81. What are the general steps for the analysis of substances? 　　Answer: It usually includes several steps such as sampling, sample weighing, sample decomposition, selection of analysis methods, separation of interfering impurities, analysis and measurement, and result calculation. 　　82. What are the three instruments used to accurately measure the volume of solutions in titrimetric analysis? 　　Answer: buret, pipette, and volumetric flask. 　　83. What is the method for lubricating an acid burette? 　　Answer: Remove the piston, and use clean paper or cloth to dry the piston as well as the inner walls of the sleeve. Dip your fingers in a small amount of Vaseline and apply a thin layer of it on both ends of the piston; do not apply Vaseline right next to the piston holes, as this could block them. After applying the Vaseline, put the piston back into the sleeve and rotate it several times in the same direction to ensure that the Vaseline is distributed evenly and the area becomes transparent. Then wrap an rubber band around it to keep the piston in place within the sleeve and prevent it from slipping out. 　　84. Gravimetric analysis? 　　Answer: It is a quantitative analysis method that determines the content of the component to be measured based on the weight of the reaction products. 　　85. Buffer solution? 　　Answer: It is a solution composed of weak acids and their salts, or weak bases and their salts, with a certain pH value; adding more of the acid or base does not cause a significant change in the solution’s pH value. 　　86. True value? 　　Answer: The actual value that exists objectively. 　　87. Acid-base titration? 　　Answer: It is a method that uses the reaction between acids and bases to determine the content of a substance, also known as the neutralization method. 　　88. Indicator? 　　Answer: It refers to the reagent used in volumetric analysis to indicate the end point of titration. 　　89. Weights? 　　Answer: It represents a unit of mass; it has a definite mass and a specific shape, and is used to measure the mass of other objects as well as to calibrate balances. 　　90. Theoretical endpoint? 　　Answer: During the titration process, the point at which the standard solution added reacts quantitatively with the substance to be analyzed according to the reaction equation, and when the reaction is complete, this point is called the theoretical endpoint. 　　91. Titration endpoint? 　　Answer: During the titration process, after adding the indicator, it is the turning point at which an external change is observed when the reaction is complete. 　　92. What is a solution? 　　Answer: A homogeneous and stable system in which molecules, atoms, or ions are dispersed within another substance is called a solution; a solution consists of a solute and a solvent. 　　93. Solubility? 　　Answer: It refers to the number of grams of a substance that can be dissolved in 100 grams of solvent at a certain temperature when a state of dissolution equilibrium is reached. 　　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 unfixed (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 part of the standard deviation relative to the mean is called the relative standard deviation. 　　98. Briefly describe what the standard addition method is 　　Answer: The standard addition method involves adding varying amounts of standard solution to several portions of the sample solution. Then, following the steps for constructing a standard curve, the absorbance is measured. An absorbance-versus-added-concentration curve is plotted, and 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. The symbol Mr, which is commonly used as a unit of measurement in analytical chemistry, 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: (A) A. The same amount of substance, B. The same mass, C. The same basic units. 　　103. For complexometric titration, it is preferable to use chemical reagents with a purity of (B) or higher. 　　A. Chemical grade, B. Analytical grade, C. Laboratory reagent. 　　104. SI is the abbreviation for (B). A. Basic units of the International System of Units, B. International System of Units, C. Legal measurement units. 　　105. When preparing standard solutions directly, it is necessary to use (C) 　　A. analytically pure reagents, B. high-purity or ultra-high-purity reagents, C. reference materials. 　　106. The number of basic units in 1 mole of any substance is equal to (A). 　　A. 0.012 Kg of 12C atoms, 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, C. Microbial action.