Analyze technical test questions

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I. True or False Questions 1. Acids that can be almost completely dissociated in solution are called strong acids. Therefore, hydrochloric acid, sulfuric acid, and hydrofluoric acid are all strong acids. (x) 2. Phosphoric acid is a triprotic acid, and three hydrogen ions can be dissociated in an aqueous solution. (v) 3. The acidity of a solution refers to the concentration of hydrogen ions in that solution, and it is commonly expressed using the pH value, where pH = log. (x) 4. The molecular formula of acetic acid is CH2CH2OH. (x) 5. Hydrogen is a flammable gas. (v) 6. Fe(OH)3 is an amorphous precipitate; slow-filter paper should be used during filtration. (x) 7. In gas analysis, KOH is commonly used as an absorbent to absorb O2. (x) 8. Chloride ions in water can react with silver ions to form a deep red precipitate with very low solubility. (x) 9. When analyzing impurities and ash in oil samples, the gravimetric method is used. (v) 10. Silica gel is placed in the dryer to keep moist materials dry. (x) 11. White light is composed of a mixture of seven monochromatic lights. Among these monochromatic lights, red light has the shortest wavelength, while purple light has the longest wavelength. (x) 12. When titrating a base with an acid standard solution, the methyl orange indicator changes from red to yellow. (x) 13. The chemical name of EDTA is disodium ethylenediaminetetraacetate. (v) 14. In redox reactions, the substance that loses electrons is called an oxidizing agent, while the substance that gains electrons is called a reducing agent. (x) 15. Significant figures refer to the digits that can actually be measured during a measurement. Rounding 0.88745 to four digits according to the rules gives 0.8875. (x) 16. The concentration of an acid refers to the total concentration of acids in a solution, including both the undissociated and dissociated acids. (v) 17. According to the ionization theory, aqueous solutions of salts formed from strong acids and weak bases are acidic. (v) 18. The density of concentrated hydrochloric acid is 1.198 g/mL, its purity is 36–38%, and its molar concentration is 18 mol/L. (x) 19. A 0.001 mol/L HCl solution, with a pH of 3. (v) 20. Aqueous solutions of sodium chloride, sodium sulfate, and sodium carbonate, with pH=7. (x) 21. Color complementarity in visible light: green light and purple light are complementary to each other. (v) 22. When dissolving the sample in aqua regia, platinum utensils can be used. (x) 23. The weighing of an analytical balance relies on the principle of levers. (v) 24. When preparing a dilute sulfuric acid solution from concentrated sulfuric acid, water should be slowly poured into a hard glass beaker containing the concentrated sulfuric acid, while stirring continuously. (x) 25. Error refers to the degree of difference between the measured value and the true value. The smaller the error, the higher the accuracy of the measured value. (v) II. Multiple-choice questions 1. Domestic reagents have unified standards and are generally divided into four grades; the first grade corresponds to high-purity reagents, denoted by GR, and the label color is green. 2. Light waves that can stimulate the retina of the human eye to produce colored vision are called visible light, with a wavelength range of approximately (400–700 nm). 3. The color of the acetylene gas cylinder is (white). 4. Any compound that contains an acid group and can have hydrogen displaced by a metal is called an (acid). 5. Acidity refers to the (H+ concentration) in a solution. 6. The solution with acid-base buffering capacity is (0.5M NaAC—0.5M HAC). 7. As the acidity of the solution increases, the chelating ability of EDTA for metal ions decreases. 8. To dilute 100 mL of 10% HCl solution to 200 mL of 5% HCl solution, (100 mL) of water needs to be added. 9. Compounds that contain complex ions are called (complexes). 10. An acid with a density of 1.42 g/mL, a percentage content of 65–68%, and a molar concentration of 15 mL is (nitric acid). 11. After electrolyzing the zinc alloy solution, the black substance on the platinum wire mesh is (PbO2). 12. When titrating free fatty acids in oil, the pH range of the phenolphthalein indicator used is (pH=8.0–9.6). 13. To determine Zn2+ in a solution by complexometric titration, (xylene orange) is used as an indicator. 14. Among the following oxides, (Al2O3) is an amphoteric oxide. 15. The approximate formula for converting the measurement results using a standard sample in photometric analysis is: C_test = C_standard / (C_standard × A_test). Here, C_test represents the concentration of the element being measured in the test solution; C_standard represents the concentration of the same element in the standard solution; A_test represents the absorbance of the test solution; and A_standard represents the absorbance of the standard solution. III. Fill-in-the-blanks: 1. In chemical analysis methods, chemical reactions can be divided into four types: acid-base neutralization reactions, redox reactions, (precipitation reactions), and complexation reactions. 2. Solid substances that are insoluble in water are called (suspended solids) and can be determined by the weight concentration method. 3. The saponification value refers to the number of milligrams of potassium hydroxide required to saponify 1 gram of the sample, expressed as (mgKOH/g). 4. To determine water hardness, (EDTA) is commonly used as a standard solution. 5. Under pH values of 9–11, Fe3+ forms (yellow) complexes with sulfosalicylic acid. 6. When determining O2 in gases using the gas absorption method, an alkaline solution of pyrogallic acid is used as the absorbent. 7. Atomic absorption spectroscopy is a method for determination based on the absorption by ground-state atoms of their (resonance emission lines). 8. The line that reflects the variation of detector noise over time, when no components to be analyzed enter the gas chromatograph detector, is called the (baseline). 9. A solution is composed of (solvent and solute). 10. An acid-base buffer solution is a type of solution that can stabilize the (acidity or alkalinity) of a solution. IV. Essay Questions 1. What is an acid-base buffer solution, and what is its function? Answer: A so-called acid-base buffer solution is a solution that can stabilize the acidity of a solution. If a small amount of acid or base is added to this solution, or if a small amount of acid or base is generated as a result of a chemical reaction, or if the solution is slightly diluted, etc., the acidity of the solution can remain essentially unchanged. 2. Explain the conditions of the titration reaction in titrimetric analysis. Answer: In titrimetric analysis, the conditions for the titration reaction are: (1) The reaction must proceed quantitatively, with no side reactions occurring ； (2) The reaction should be completed rapidly; if the rate is slow, methods such as heating or adding a catalyst can be used to speed up the reaction ； (3) There are relatively simple and reliable methods to indicate the equivalence point ； (4) The co-existing substances do not cause interference or can be masked. V. Calculation Problems 1. A sample of iron ore weighing 0.2000 g was taken, and the total iron content was determined using the K2Cr2O7 method. 42.35 mL of a standard K2Cr2O7 solution with a concentration of 0.008333 mol/L was used. Determine the iron content in the ore (Fe%). (Fe=55.85) 2. To determine the percentage content of silicon in pig iron by gravimetric analysis, 1.000 g of the sample is weighed, and 0.0208 g of SiO2 is obtained; calculate the percentage content of silicon (Si%). (Si=28.086, O=16)