Automatic potentiometric titrator JH-T7 titration method calibration low concentration silver nitrat

1. Project background
Silver nitrate solution is widely used in chloride ion detection and other fields. In practice, it is very important to accurately calibrate the low concentration silver nitrate solution if the concentration is unknown. This scheme uses the automatic potentiometric titrator of Shanghai Jiahang Instrument Co., Ltd. to provide an accurate and reliable method for calibration of low concentration silver nitrate by optimizing the experimental conditions.

2. Instruments and reagents
(1) Instruments
Selected Shanghai Jiahang [JH-T7] automatic potentiometric titrator, with composite silver electrode, equipped with 10mL burette. The instrument has the functions of high-precision titration control, real-time potential monitoring and data processing, which can meet the needs of experiments.

(2) Reagents
1. Acetone (AR) : analysis pure grade, used to adjust the reaction environment, enhance the potential jump.

2. Glacial acetic acid (AR) : analysis of pure, to help create suitable reaction conditions.

3. Silver nitrate titrator: to be calibrated, the concentration is about 0.002mol/L.

4. First-level water: Ensure the purity of the experimental water and avoid interference from impurities.

5. Reference sodium chloride reagent: After drying treatment, used to prepare standard sodium chloride solution.

3. Experimental methods
(1) Experimental preparation
1. Accurately weigh 575.36mg dried standard sodium chloride reagent, place it in a 1L volumetric bottle, fill it with primary water to the scale line, and shake it well for use. This standard sodium chloride solution concentration is a specific value, which is the key basis for the calibration of silver nitrate solution.

2. Check the automatic potentiometric titrator and supporting electrodes to ensure the normal operation of the instrument and good electrode performance. Perform parameter setting and initialization calibration according to the instrument operating manual.

(2) titration operation
1. Accurately remove 1mL of the prepared sodium chloride solution and put it into the titration cup. Add 50mL acetone and 2mL glacial acetic acid and stir gently until the solution is well mixed. The environment created by acetone and glacial acetic acid can improve the obvious degree of potential jump and facilitate the accurate determination of titration end point.

2. Insert the composite silver electrode into the solution, start the automatic potentiometric titrator, and perform reverse titration with the unknown concentration of silver nitrate solution. Set the titration type as dynamic titration, and set reasonable instrument parameters according to instrument performance and experimental requirements. If the titration rate is selected very slowly, ensure that the reaction is fully carried out; The electrode balance time is set to 4s to ensure the electrode potential is stable. The pre-stirring time is 10s to make the solution evenly mixed.

3. During the titration process, the instrument monitors the potential change in real time. When the potential jumps, the instrument automatically determines the titration end point and records the titration volume. At the same time, the blank test is carried out to eliminate the possible systematic errors in the experiment.

4. Result calculation
(1) Calculation formula
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I. Program overview
In the field of chemical analysis, silver nitrate solution is often used to detect chloride ion content, and the accurate calibration of its concentration is very important. The automatic potentiometric titrator JH-T7 from Shanghai Jiahang Instrument Co., Ltd. can accurately measure the concentration of low concentration silver nitrate solution. The method of using the instrument to calibrate low concentration silver nitrate is introduced in detail in this scheme, aiming to provide accurate and efficient operation guidance for related experiments.

2. Instruments and reagents
(1) Instruments
1. Automatic potentiometric titrator JH-T7: With high-precision titration system, can precisely control the amount of titration liquid added; It has a high-sensitivity potential detection module, which can monitor the change of solution potential in real time. Equipped with intelligent data processing system, it can automatically record titration data, draw titration curve and calculate the result.

2. Composite silver electrode: as a key component of potential measurement, its stability and accuracy directly affect the experimental results. Before use, check the appearance of the electrode to ensure that there is no damage and pollution, and activate it according to the instructions to ensure the measurement accuracy.

3.10mL burette: used with titrator to accurately measure silver nitrate titrant. Before use, it is necessary to calibrate the burette to ensure that its calibration is accurate.

(2) Reagents
1. Acetone (AR) : analysis pure grade, used in the experiment to improve the reaction environment, increase the obvious degree of potential jump. Its purity should be ensured to avoid interference of impurities with the experimental results.

2. Glacial acetic acid (AR) : analysis pure, synergistic with acetone, optimize the reaction conditions. When storing, pay attention to sealing to prevent volatilization.

3. Silver nitrate titrator: to be calibrated, the concentration is about 0.002mol/L. The solution should be kept in brown reagent bottles to avoid decomposition by light.

4. Primary water: used to prepare standard sodium chloride solution and clean experimental equipment to ensure the high purity of experimental water and reduce the influence of impurities in water on the experiment.

5. Reference sodium chloride reagent: before use, it should be dried to constant weight at a specific temperature, and a certain mass should be accurately weighed for preparing standard sodium chloride solution, and the accuracy of its quality is directly related to the reliability of the calibration results.

3. Experimental steps
(1) Preparation of standard sodium chloride solution
Accurately weigh 575.36mg of dried reference sodium chloride reagent and place it in a 1L volumetric bottle. Slowly add the primary water, stirring as you go, until the sodium chloride is completely dissolved. Then fill with primary water to the scale line, shake well, prepare a standard sodium chloride solution for use. The concentration of this solution is an important basis for calculating the concentration of silver nitrate solution.

(2) Instrument parameter setting
1. Turn on the power supply of automatic potentiometric titrator JH-T7, start the instrument, and wait for the instrument self-test to be completed.

2. Enter the parameter setting interface and make the following Settings according to the experimental requirements:

* Titration type: Select the dynamic titration mode, which can automatically adjust the titration speed according to the potential change, to ensure that the titration process is more accurate and efficient.

* Burette volume: Set to 10mL, consistent with the actual burette specifications.

Working electrode: Choose composite silver electrode.

* Reference electrode: Set it correctly according to the instrument instructions and experimental requirements (if no additional reference electrode is required in this experiment, set it as none according to the document).

* Sample unit of measurement: set as the appropriate unit (consistent with the experimental document in this experiment, without special instructions can not change the default setting).

* Titration display unit: set to mv to monitor potential changes.

* Liquid replenishment speed: set to 7 (can be fine-tuned according to the actual situation to ensure the timeliness and stability of titrant replenishment).

* Stirring speed: set to 8 to ensure that the solution is evenly mixed and the reaction is fully carried out, but care should be taken to avoid bubbles resulting from too fast stirring speed affecting the experimental results.

* Electrode balance time: set to 4s, so that the electrode reaches a stable state before measurement, to ensure the accuracy of potential measurement.

* Electrode balance potential: set to 1 (the specific value is determined according to the instrument instructions and experimental conditions to ensure that the electrode is in the best working condition).

* Pre-mixing time: set to 10s, so that the added reagents are fully mixed to ensure the uniform reaction system.

* Minimum addition volume: Set to 0.02mL to ensure the accuracy of titration solution addition during titration.

* End volume: Set to 20mL (can be adjusted according to the expected titration volume and experimental requirements).

* Titration speed: The selection is very slow, so that the reaction is fully carried out, easy to accurately capture potential jumps.

* Equilibrium potential before titration: set to 10mv to ensure that the potential is stable before titration begins.

* Pre-titration add volume: set to 0mL.

* Potential jump: Set to 200 (this value is determined according to experimental experience and instrument performance, used to judge the titration end point).

* Pre-controlled mv value: set to 3.545 (related to instrument detection accuracy and experimental conditions to ensure the stability of the titration process).

* Correlation coefficient Result unit: Set according to experimental requirements and data processing requirements (CV1/ma in this experiment according to the document).

* Calculation formula: used to automatically calculate the concentration of silver nitrate solution,

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Where: C is the molar concentration of silver nitrate standard solution (mol/L),

V is the volume (mL) of silver nitrate standard solution consumed during titration.

m is the mass of sodium chloride used (mg),

Vo is the volume (mL) of blank silver nitrate consumed.

(3) titration operation
1. Accurately remove 1mL of the prepared sodium chloride solution and place it in a clean and dry titration cup.

2. Add 50mL acetone and 2mL glacial acetic acid to the titration cup and gently shake the titration cup to mix the solution evenly.

3. Carefully insert the composite silver electrode into the titration cup, ensuring that the electrode head is completely immersed in the solution to avoid contact with the cup wall or the formation of bubbles.

4. Start the titrator and start back titration with an unknown concentration of silver nitrate solution. During the titration process, the change of potential and the trend of titration curve were closely observed. When the potential jump is obvious and the pre-set potential jump is reached, the titrator automatically determines the titration end point and records the titration volume.

5. Carry out blank test at the same time, that is, without adding sodium chloride solution, add acetone and glacial acetic acid according to the same operating steps, titrate with silver nitrate solution, and record the volume of silver nitrate consumed in blank.

Iv. Data processing and result analysis
(1) Data recording
After each titration is completed, the experimental data such as titration volume and blank volume are recorded in time. Repeated titration experiments (usually 3-5 parallel experiments) to improve the reliability of experimental results.

(2) Concentration calculation
According to the set calculation formula, the solution concentration of silver nitrate obtained by each titration is calculated automatically by titrator. The average of the results of multiple parallel experiments was calculated as the final calibration silver nitrate solution concentration. At the same time, the relative deviation between each measurement value and the average value was calculated to evaluate the repeatability of the experimental data.

(3) Evaluation of results
1. Repeatability evaluation: If the relative deviation of multiple parallel experiments is within the allowable range (generally determined according to the experimental requirements and relevant standards, such as the relative deviation does not exceed ±2%), it indicates that the experimental data is good in repeatability and the experimental results are reliable.

2. Accuracy evaluation: Compare the calibration results with the known accurate concentration of silver nitrate solution (if any), or with the theoretical calculation value to evaluate the accuracy of the calibration results. If the deviation is within a reasonable range, it indicates that the experimental method and instrument operation are accurate and reliable. If the deviation is large, it is necessary to check the experimental process, instrument parameter setting and other links, find the cause and re-perform the experiment.

5. Precautions
1. Before the experiment, ensure that all instruments and equipment are clean and dry, and the electrode performance is good. Calibrate and maintain the titrator regularly to ensure the accuracy and stability of the instrument.

2. The drying temperature and time of the benchmark sodium chloride reagent should be carried out in strict accordance with the standard method to ensure the accuracy of its quality. In the weighing process, use a balance with appropriate precision and follow the correct weighing operation specifications.

3. Acetone and glacial acetic acid are volatile and irritating, and the experiment should be carried out in a well-ventilated environment. Wear protective equipment, such as gloves and goggles, to avoid contact with skin and eyes.

4. During the titration process, avoid solution splashing or electrode collision. If the solution has abnormal conditions (such as discoloration, precipitation, etc.), the titration should be stopped in time, the reason should be analyzed and the corresponding measures should be taken.

5. After the end of the experiment, clean the titration cup, electrode and other experimental equipment in time, and properly store the equipment and reagents. The waste liquid generated from the experiment should be treated in accordance with environmental protection requirements to avoid polluting the environment.