Manual for laboratory classes in biological physics. Коллектив авторов

and concentration of 80 g/l is prepared. The solution must stand after cooking for at least 8 hours. In another option for making «zero-solution 10±0,5 g of sodium sulfite (Na₂SO₃) is dissolved in 200 ml of tap water and add 20-50 mg of soluble salts of silver or cobalt (e.g. cobalt chloride – CoCl₂). Addition of salts of heavy metals is used as the catalyst for the oxidation of sodium sulfite. After 10 minutes, «Zero-solution» may be used for calibration.

      Place the sensor in an environment with zero oxygen content, and to calibrate the zero point of the device.

      Calibrating by the air.

      At this calibration atmospheric air, which is saturated with water vapor, can be used as a standard sample with known oxygen content.

      Place the sensor into a bottle with a small amount of water so that the sensor does not touch the water. Calibrate the top point of the device.

      The quality of the calibration and accuracy of the results of subsequent measurements is significantly affected by the temperature measurement accuracy. During measurement should not forget about another important factor – the pressure. Atmospheric pressure has a directly proportional effect on the solubility of oxygen in liquids, freely contacting with atmospheric air, so it must take into account the values during the calibration and measurement.

      Table 4.1

      The solubility of oxygen in distilled water, saturated with air at a pressure of 101.3 kPa (760 mm Hg).

      When working with the amperometric sensor it should be cautious, protecting the glass sleeve from impacts. It is not allowed to apply mechanical stress to the cable. For prolonged storage, when amperometric sensor is off (for more than 6 months) it is necessary to drain the electrolyte solution, wash the corps of the sensor with distilled water and put it on the amperometric sensor.

      When there are shorter work breaks, and between the series of analyzes, amperometric sensor is preferably stored in water vapor. In order to do this, select one flask, pour 10-15 ml of distilled water and set amperometric sensor without touching the sensitive part of the sensor to the surface of the flask. Storing the sensor in this position (in water vapor) between measurements and long periods of time can significantly increase the time of routine service of sensor.

      Laboratory work № 7

      Determination of the oxygen content dissolved in water

      Objective: Measurement of the oxygen content in the water.

      Tasks:

      1. To perform calibration of device on standard solutions.

      2. To measure the amount of oxygen in the water

      4. To build a graphic of values

      5. To make conclusions about the observed phenomena and to prepare a report.

      Equipment and materials: Laboratory amperometric analyzer, bottles of 300 ml, microcompressor, barometer, thermometer, 8 % solution of sodium sulfide, salt CoCl_2, electro-mechanical mixing device.

      Procedure:

      1. To perform the necessary training and the setting of the device (see. Chapter 4);

      2. To prepare the workplace, distilled and tap water. To rinse the sensor and detector with distilled water;

      3. To lower the detector and the sensor into the solution, stir it to accelerate the achievement of temperature regime. Turn on the device;

      4. To turn on the electromechanical mixing device and after 5-7 minutes remove the instrument readings;

      5. To measure the temperature of the test sample;

      6. To measure the atmospheric pressure;

      7. To turn off the electromechanical mixing device.

      Task:

      1. To measure the oxygen content in distilled water;

      2. To measure oxygen content in the distilled water saturated with oxygen in the air for 30 minutes – barbotage;

      3. To measure the oxygen content in tap water.

      Report design. To make all calculations by all measurements of the oxygen content of the samples taking into the factor of atmospheric pressure, using the formula 4.1 and Table. 4.1. Compare measurement results and make conclusions.

      Laboratory work № 8

      Amperometric method of determining the rate of respiration of aquatic plants and yeast cells

      Objective: To determine the intensity of respiration of aquatic plants, yeast suspension in normal conditions and in the action of various factors.