Shenzhen University Physical Chemistry Experiment Report

Shenzhen University Physical Chemistry Experiment Report

Experimenter: Lai Kaitao, Zhang Zhicheng Experimental time: 2000/4/3

Temperature: 21.6 °C Atmospheric pressure: 101.2 kPa

Experiment 1 assembly and performance test of constant temperature water bath

Objective To understand the structure and construction principle of constant temperature water bath, learn the assembly technology of constant temperature water bath, measure the sensitivity curve of constant temperature water bath, and master the adjustment technology and correct use method of Beckmann thermometer. Instruments and reagents

5 liter beaker Beckman thermometer precision thermometer heater

Mercury contact thermometer relay stirrer transformer

Experimental procedure

3.1 Experimental equipment, install the mercury switch, stirrer, etc. Wire and check according to the circuit diagram.

3.2 Inject distilled water into the large beaker. Adjust the mercury switch to about 30 °C and tighten the locking screw. Adjust the voltage transformer to 220V, start the agitator, turn on the relay power and heating power. At this time, the relay white light is on, indicating that the water temperature in the beaker has not reached the preset 30 °C. After a period of time, the white light goes out, indicating that the water temperature has reached 30 ° C, and the relay automatically cuts off the heating power.

The Beckmann thermometer was adjusted to read about 2 ° C in a 30 ° C water bath. Install the Beckman thermometer. Turn off the blender. The Beckman thermometer readings were recorded every 1 minute and a total of 12 were recorded. Start the stirrer and stabilize the reading of the Beckman thermometer every 1 minute after 2 minutes of stabilization. A total of 12 records were recorded. Adjust the voltage regulator to 150V, stabilize for 5 minutes, and then record the Beckman thermometer reading every 2 minutes, a total of 10 records. After the experiment is completed, put the Beckman thermometer back into the protection box and adjust the voltage transformer to 0V. Turn off the power to each instrument and unplug the power cord. Remove the wiring.

4 experimental data and its processing

Table 1 Temperature change of constant temperature water bath under different conditions, °C

Figure 1 Sensitivity curve of constant temperature water bath under different conditions

discuss

5.1 Factors affecting sensitivity are related to the working medium, temperature sensing element, stirring speed, heater power, and physical properties of the relay. If the heater power is too large or too low, it is difficult to control the temperature of the water bath so that its temperature fluctuates greatly above and below the set temperature, and its sensitivity is low; if the stirring speed is high or low, or is always too low, the constant temperature water bath The temperature fluctuates up and down at the set temperature, and the measured sensitivity is low. If the accuracy of the Beckman thermometer is low, the difference in temperature changes recorded at different times is large, that is, the temperature of the water bath fluctuates greatly at the set temperature, and the sensitivity is low; similarly, the temperature sensing effect of the contact thermometer is poor. When the temperature is higher than the set temperature, the heater does not stop heating, so that the bath temperature drops slowly, so that the temperature of the bath bath is fluctuated up and down at a set temperature in different time, and the measured sensitivity is low.

5.2 In order to improve the sensitivity of the constant temperature bath, a moderately-powered heater, a high-precision Beckman thermometer contact thermometer, and a stirrer used in the mercury thermometer should be fixed at a moderate value, and at the same time according to the constant temperature range. Select the appropriate working medium.