Assessment Test Paper for pH Meter and Ion Meter Courses

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The assessment test papers for acidimeters and ion meters cover the JJG757-2007 Calibration Regulations for Ion Meters and the JJG119-2005 Calibration Regulations for Laboratory pH (Acidity) Meters, and are used to evaluate the professional skills of chemical calibration technicians. I. Fill-in-the-blank questions (2 points each, total 20 points) 1. In 100 mL of a 0.1 mol/L NaOH solution, the mass of NaOH present is (0.4) grams (the molecular weight of NaOH is 40). 2. A saturated potassium chloride solution is commonly used as a salt bridge in pH measurements; its function is to reduce the (junction) potential. When the solution being tested contains substances that can react chemically with chloride ions, a solution of (non-chloride salts) should be used as a salt bridge. 3. According to the calibration procedures for pH meters, in the calibration conditions for pH meters of class 0.1, the temperature stability of the standard solution and the electrode system is required to be (0.5)°C. 4. The calibration items for the meter reading specified in the pH meter calibration regulations are (meter reading error) and (repeatability of meter reading). 5. A 0.01 mol/L borax solution is (alkaline); the distilled water used to prepare this solution should have any (carbon dioxide) dissolved in it removed. 6. Sulfuric acid is a strong acid; in an H2SO4 solution with a concentration of 2 mol/L, the concentration of H+ ions is (4) mol/L. When phenolphthalein indicator is added to this solution, the solution has (no) color. 7. The main factors affecting the measurement by ion-selective electrodes are (interfering ions), (ion strength), and (potential drift). 8. The molecular weight of disodium hydrogen phosphate is (141.96), and its molar mass is (141.96 g/mol). (Known: Na=22.99, H=1.01, P=30.97, O=16.00) 9. The mass molar concentration of a solution refers to the amount of substance of the solute per (1) kilogram of solvent, and its unit is mol/kg. 10. A 0.05 mol/kg solution of potassium hydrogen phthalate is acidic; the distilled water used to prepare this solution does not need to have the (carbon dioxide) dissolved in it removed. Instrument test questions: yunrun.com.cn/tech/list_101.html II. True or False questions (2 points per question, 20 points in total.) Mark ✔ for correct and ✘ for incorrect) 1. The insulation resistance between the power phase and neutral wire of the ion meter, and ground (chassis), should be no less than 10 MΩ. ✘ 2. For specialized ion meters that use electrodes with low internal resistance for measurement, input impedance and input current may not be required. ✔ 3. When measuring the insulation resistance of the ion meter, the power plug must be connected to the power supply, and the power switch should be set to the on position. ✘ 4. For subsequent inspections, if there are any non-conformities in the key items, it is determined as non-conforming. ✘ 5. For instruments whose metrological performance may change after repair or long-term storage, subsequent verification shall be carried out in accordance with the requirements for initial verification. ✔ 6. A laboratory pH meter is an electrochemical analytical instrument. ✔ 7. The pH meter measuring electrodes include an indicator electrode and a calomel electrode. ✘ 8. For instruments of grade 0.01, first-grade pH reference materials should be used, while instruments of other grades can use second-grade reference materials. ✘ 9. Standard DC potential signal sources such as pH meter calibrators or DC potentiometers shall have an accuracy higher than that of the electrical measuring instrument being calibrated. ✔ 10. The instrument can be set to measure either pH or mV, depending on the user’s requirements. ✔ III. Multiple-choice questions (2 points per question, total 20 points) 1. The potential of the calomel electrode has the following property (c). a. It is related to the pH value of the solution in contact with it ； b、It is related to the type of salt bridge in contact with it ； c. Related to the concentration of chloride ions constituting the electrode ； d. It is independent of the operating temperature of the electrode. 2. The concentration of a saturated potassium hydrogen tartrate (KHC4H4O6) solution at 25°C is 0.034 mol/L. How many grams of potassium hydrogen tartrate are required at least to prepare 500 mL of this solution? (a) (Atomic weight K=39.1 ； C=12 ； H=1.01 ； O=16) a, 3.2g ； b. 0.32g ； c、6.4g ； d, 0.64 g. 3. The ion selectivity coefficient depends on (a, b, c). (Multiple choice) a. Types of ions being compared ； b. Ionic strength of the solution ； c. Solution temperature ； d. Solution pH value: 4. Arrange the solutions of H2SO4, KOH, KHCO3, KHSO4, and K2CO3 with the same molar concentration in order of decreasing pH value in the blank (d). a、KOH, KHCO3, K2CO3, KHSO4, H2SO4 b、KOH, K2CO3, KHSO4, KHCO3, H2SO4 c、H2SO4, KHSO4, KHCO3, K2CO3, KOH d、KOH, K2CO3, KHCO3, KHSO4, H2SO4 5、At 25°C, the sum of the pH value and the pOH value in an aqueous solution of pure water is equal to (c); the pOH of a 0.01 mol/L NaOH solution is 2, and its pH is equal to (c). a、14 ； 10 b, 0 ； 2 c, 14 ； 12 d, 0 ； 12 6. The maximum operating temperature for a calomel electrode is around (d)°C; above this temperature, (d) will decompose, resulting in unstable electrode potential. a. 70 ； Electrode b, 50 ； Calomel c, 50 ； Electrode d, 70 ； Mercuric chloride 7: According to the specifications for pH meter calibration, a pH meter of class 0.001 has a division value of (a)pH, and the total error in the instrument’s readings should not exceed (a)pH. a、0.001 ； ±0.01 ； b、0.001 ； ±0.005 ； c、0.002 ； ±0.01 ； d、0.002 ； ±0.005. 8. The pH standard solution shall possess the following properties (a). a. Larger buffer capacity ； b、Larger temperature coefficient ； c. Larger dilution values ； d. Higher density. 9. The indicated value error specified in the calibration regulations for ion meters is (b). a. Relative error ； b. Absolute error ； c、Citation error ； d. Basic error. 10. The function of the temperature compensator in a pH meter is (a). a. Compensation for the change in the slope of the glass electrode with temperature ； b. Compensation for the change in electromotive force of the pH measurement cell with temperature ； c. Change in the potential of the compensated calomel electrode with temperature ； d. The change in the resistance of the compensation electrode with temperature. IV. Short-answer questions (10 points per question, 20 points in total) 1. What properties should pH standard buffer solutions have? Answer: pH standard buffer solutions should have good reproducibility and stability. Therefore, it should have a large buffer capacity, small leakage current, and a small temperature coefficient. 2. Please briefly describe the method used to measure the pH value of a solution using a pH meter Answer: A comparative method should be used for measurement. First, a cell is formed using an indicator electrode, a reference electrode, and a pH standard buffer solution; the electromotive force generated by this cell is fed into the pH meter to “calibrate” the instrument” ； Then, a battery is formed using the test solution and the same pair of electrodes; the electromotive force of this battery is also input into the potentiometer ； Upon comparison, the value displayed on the meter is the pH value of the solution being measured. V. Calculation questions (20 points for each question, 20 points in total) 1. A technician is calibrating the input current of an ion meter and obtains a value of 6. What is the input current of this instrument? Answer: 10-13A. 2. A certifier conducted a test on the repeatability of the pH meter’s indicated value; by using a pH meter, a standard pH value of 10.0000 was input into the meter, and the indicated pH value was recorded as 10.01 ； 10.01 ； 10.00 ； 9.99 ； 10.01 ； 9.99. If repeatability is expressed as the standard deviation of a single measurement, what is the repeatability of the meter’s electrical indication? Answer: The repeatability is 0.01.