Wep distilled water. Specific electrical resistance of distilled water. pH - hydrogen indicator. Description of the PWT Hanna Instruments Conductometer. Concept and characteristics
Basic information. Conductivity measurement aqueous solutions has become widespread in laboratory practice, with automatic chemical control of the water regime of steam power plants, the efficiency of water purification plants and industrial heat exchange and other installations, as well as various quality indicators characterizing chemical technological processes.
Technical means designed to measure the specific electrical conductivity of aqueous solutions are commonly called conductometric liquid analyzers. The scale of secondary instruments of liquid conductometers (laboratory and industrial) for measuring electrical conductivity is graduated in units of siemens per centimeter or microsiemens per centimeter are called saline. The scale of secondary instruments of salt meters is graduated according to (for the conditional content of these salts in a solution) in the following units: milligram per kilogram microgram per kilogram or milligram per liter and microgram per liter Liquid conductometers used to measure the concentration of solutions of salts, acids, alkalis, etc. ., are often called concentrators. The scale of the secondary devices of the concentrators is calibrated as a percentage of the mass concentration value. Conductometric liquid analyzers are also used as signaling devices.
With increased requirements for the quality indicators of feed water, steam and condensate, it is necessary to measure small values of electrical conductivity, not exceeding 5-b
Measurement of the electrical conductivity of aqueous solutions is usually carried out using an electrode conductometric measuring transducer, consisting of two electrodes,
located in a vessel into which a controlled aqueous solution enters. The design of these transducers and the measuring circuits used for liquid conductometers are discussed below. To measure the electrical conductivity of solutions, electrodeless liquid conductometers are also widely used.
The electrical conductivity is the reciprocal of the resistivity:
Here, electrical conductivity, resistivity, Ohm-cm, determined by the expression
where is the electrical resistance of a fixed volume of solution with concentration C between metal electrodes, Ohm; effective cross-section of the solution through which the current flows, the distance between the electrodes, see
According to equation (22-2-2), expression (22-2-1) becomes:
where is the electrical conductivity of a fixed volume of solution, Ohm; constant of the electrode transducer,
From expression (22-2-3) we have:
For transducers with a simple electrode configuration, the constant can be determined by calculation. If the transducer has a complex design, then the constant is determined experimentally.
It should be noted that based on the study of the specific electrical conductivity, we are not able to compare the values of the electrical conductivity of solutions with each other depending on their concentration. This becomes possible with the introduction of the concept of equivalent electrical conductivity. Kohlrausch called the equivalent electrical conductivity the quantity
where is the equivalent electrical conductivity, Cm-eq; is the equivalent concentration of the solute, .
The value of the electrical conductivity of solutions depends not only on the equivalent concentration and equivalent electrical conductivity, but also on the degree of electrolytic dissociation of the solution.
Therefore, in the general case, when not all molecules have decayed into ions, for the electrical conductivity we obtain the following equation:
Here is the degree of electrolytic dissociation, i.e. the ratio of the number of dissociated electrolyte molecules to the total number of dissolved molecules. Electrolytes are substances whose aqueous solutions conduct electricity (salts, alkalis and acids). The degree of electrolytic dissociation a depends both on the nature of the solute and on the concentration of the solution. The numerical value of a increases with the dilution of the solution. Depending on the degree of electrolytic dissociation, electrolytes are divided into strong (hydrochloric, sulfuric, nitric acids, alkalis, almost all salts) and weak (for example, organic acids). For strong electrolytes, which in aqueous solutions at low concentrations almost completely decompose into ions, the value of a is taken equal to unity.
Rice. 22-2-1. The dependence of the electrical conductivity of aqueous solutions of certain substances on their concentration at 18 ° C.
Equation (22-2-6) can be represented as follows:
where the mobility of cations and anions, respectively,
Ion mobilities are the product of their absolute velocity and the Faraday number
The electrical conductivity of aqueous solutions is in a complex dependence on the concentration of the solution. On fig. 22-2-1 shows the dependences of the specific electrical conductivity of aqueous solutions of certain substances on their concentration. It can be seen from this graph that an unambiguous relationship between the electrical conductivity of the solution and the concentration takes place only if the electrical conductivity measurements are performed in the region of relatively low concentrations. The concentrations of dissolved substances, which have to be determined when monitoring the quality of steam, condensate, feed and boiler water, correspond to the initial sections shown in Fig. 22-2-1 curves, where the electrical conductivity increases continuously with increasing concentrations.
When measuring the electrical conductivity of steam condensate and feed water, which are aqueous solutions with a very low salt concentration, the degree of electrolytic dissociation can be
take equal to one. In this case, the simplified equation can be used to determine the electrical conductivity
Here, the equivalent electrical conductivity at infinite dilution, which is given by
where are the mobilities of cations and anions, respectively, at infinite dilution of the solution (for .
The values and temperature coefficients of ion mobilities corresponding to a temperature of 18 ° C are given in. When measuring the specific electrical conductivity of aqueous solutions, the temperature is usually taken as normal (initial), for which data on electrical conductivity are given.
When measuring electrical conductivity, it is necessary to take into account the effect of the temperature of the solution on the readings of the device, since with a change in the temperature of the solution by 1 ° C, its electrical conductivity changes by This determines the importance of maintaining a constant temperature of the analyzed solution when measuring electrical conductivity or using an effective automatic temperature compensation that reduces the effect of fluctuations in the temperature of the solution to the instrument readings.
The dependence of the electrical conductivity of aqueous solutions on temperature at small deviations from 18 ° C is expressed by the formula
At a temperature that differs from 18 ° C by 10-25 ° C or more, it is necessary to use the equation
where temperature coefficient conductivity according to the formula
Here, the temperature coefficients of mobility, respectively, of the cation and anion
The temperature coefficient of electrical conductivity, according to Kohlrausch, is related to the coefficient by the ratio
The dependence of the electrical resistance of a fixed volume of solution between the electrodes of the transducer on a temperature slightly different from 18 ° C is expressed by the formula
At a temperature that differs from 18 ° C by 10-25 ° C or more, you should use the equation
When monitoring the water regime of power plants, the salt concentration is usually expressed in milligrams per liter or micrograms per liter. The equivalent concentration is used in the above equations. These concentrations are recalculated according to the formula
where the equivalent concentration, C-concentration, is the equivalent mass of the ions of the solute, according to the formula
Here, the equivalent mass, respectively, of the cation and anion of the solute (for. The values of the equivalent masses of ions of substances encountered when measuring the electrical conductivity of aqueous solutions are given in.
It was noted above that the calibration of liquid conductometers (salt meters) is carried out according to, i.e., the conditional content of this salt in a solution. This is due to the fact that among the various salts contained in the steam condensate and feed water of steam generators, sodium chloride has an average electrical conductivity.
The electrical conductivity of an aqueous solution at low concentrations and at initial temperature C can be determined taking into account expressions (22-2-8), (22-2-9) and (22-2-16) according to the equation
Substituting values into this expression, we get:
Liquid conductometers (salt meters) are usually calibrated at normal temperature. To convert to the temperature value, you can use the formula (22-2-10)
Substituting the values into this equation, we get:
The electrical resistance of a fixed volume of the converter solution at its low concentration and at a temperature of C can be determined taking into account expressions (22-2-3) and (22-2-20) by the formula
In the steam condensate and feed water of steam generators, in addition to a small amount of salts, dissolved gases are usually present - ammonia and carbon dioxide and hydrazine. The presence of dissolved gases and hydrazine changes the electrical conductivity of the condensate and feed water, and the readings of the liquid conductometer (salt meter) do not unambiguously correspond to the conditional salt content, i.e., the value of the dry residue obtained by evaporation of condensate or feed water. This leads to the need to make corrections to the instrument readings or to use an additional device to remove dissolved gases and hydrazine from the sample.
An additional device in the form of a degasser for removing dissolved gases from the sample does not exclude the effect on the readings of the hydrazine conductometric analyzer. The currently used filter filled with brand cation exchanger makes it possible to eliminate the influence of ammonia and hydrazine on the readings of the device.
Electrode conductometric transducers. Electrode transducers used to measure the electrical conductivity of solutions are made for laboratory studies of various solutions and for technical measurements. Measurements in laboratory conditions are made on alternating current. At the same time, it should be noted that the conductometric method of measurement on alternating current remains generally accepted in everyday laboratory practice. Technical measurements of the electrical conductivity of solutions using electrode transducers are usually carried out on alternating current with a frequency of 50 Hz.
The device, dimensions, and, consequently, the constant of the electrode transducers largely depend on the measured value of the electrical conductivity of the solution. In technical measurements, transducers with cylindrical coaxial and, to a lesser extent, flat electrodes are most common. The device of converters with cylindrical coaxial electrodes is schematically shown in fig. 22-2-2. The converter shown in Fig. 22-2-2, a, the outer cylindrical electrode is also its body. The second transducer (Fig. 22-2-2, b) also has cylindrical coaxial electrodes, but they are located in its steel case, to which one electrode is welded. This converter
used in TsKTI salt meters with small-sized concentrators. A degassed and enriched sample, which has a constant temperature close to 100 ° C, enters the converter through the left fitting from the concentrator. The scheme of the transducer device with flat electrodes is shown in fig. 22-2-3. A feature of the converter shown in fig. 22-2-3 lies in the fact that the areas of its electrodes and the effective cross section of the solution through which the current flows are not the same.
Rice. 22-2-2. The device of converters with cylindrical coaxial electrodes. 1 - clamps for connecting wires; 2 - electrodes; 3 - steel case; 4 - insulators.
Rice. 22-2-3. Converter device with flat electrodes. 1 - converter case; 2 - clamps for connecting wires; 3 - electrodes.
In addition to the considered flow electrode transducers, they are also of the submersible type, directly immersed in a pipeline with a liquid, the electrical conductivity (or concentration) of which must be controlled. Transducer electrodes for technical measurements are made of stainless steel. Transducer electrodes for laboratory studies of electrolyte solutions are made of platinum. To reduce the polarization of the electrodes, they are coated with a layer of platinum black. The vessels of these converters are usually made of glass. The dimensions of the vessels are chosen depending on the expected value of the electrical conductivity of the test solution.
Complex electrochemical processes take place on the electrodes of the transducer in contact with the solution. The space between the electrodes is filled when measuring the electrical conductivity of aqueous solutions with a medium with a high value of the dielectric constant. For these reasons, the fixed volume of solution between the electrodes of the transducer, when measured on alternating current, represents a complex electrical resistance - a combination of active
and capacitive components. The equivalent electrical circuit of the electrode converter, taking into account the electrode processes, is shown in fig. 22-2-4. Electrode processes include the process of electrolysis of a solution when an electric current passes through it and the process of formation of a double electric layer at the interface between the media "metal of the electrode - solution". The formation of a double electric layer occurs due to the action of an external electric field, the inequality of the chemical potentials of the metal ions of the electrodes and ions in solution, and the specific adsorption of ions and polar molecules. In an alternating current circuit, the electrical double layer is equivalent to electrical capacitance. The electrical capacitance of the double layer does not depend on the frequency of the supply voltage and is a function of the concentration and size of the potential applied to the electrodes.
Rice. 22-2-4. Equivalent electrical circuit of the electrode transducer.
The equivalent electrical circuit of the polarization process is represented in the general case by a nonlinear active-capacitive resistance, which is called the Faraday impedance. One of the equivalent circuit models is defined by the expression
where constant, Ohm - angular velocity, rad / s When performing technical measurements, they strive to create such a design of the electrode transducer so that its impedance is determined by the active resistance of a fixed volume of solution between the electrodes, and the influence of electrochemical processes and the reactive components of electrical resistance due to these processes would be negligible . If these conditions are met with the required approximation, then the electrical resistance of a fixed volume of solution between the electrodes of the transducer is determined according to the expression (22-2-3) by the following formula:
Rice. 22-2-5. Simplified equivalent electrical circuit of an electrode transducer.
Consider a simplified equivalent wiring diagram electrode transducer, which does not take into account the effect of electrolysis. In this case, the impedance of the converter will be determined, as follows from the circuit shown in fig. 22-2-5, by double-layer capacitances on the electrodes by the active electrical resistance of the solution between the electrodes and the capacitance shunting this resistance. Capacity can be called "constructive". It should be noted that water has a large value of relative permittivity compared to other liquids (for condensate at which leads to the need to take into account the capacitance between the electrodes.
Using the known relation that determines the capacitance modulus, it is possible to conduct a qualitative analysis of the influence of capacitive components and frequency on the transducer impedance modulus.
Assuming that the active resistance does not depend on the frequency of the voltage on the electrodes, it is easy to see that with increasing relative influence of the double layer capacitance on the total resistance modulus decreases, and the “constructive” capacitance increases. It can be shown that the relative effect of capacitance is practically independent of the shape of the electrodes, their mutual
location and distance between them. Indeed, structural changes affect almost equally the active resistance of the converter and the capacitance value. The degree of influence of the double layer capacitance can be changed by constructive methods. With an increase in the area of the transducer electrodes, the capacitance of the double layer increases, and a decrease in the area of the effective cross section of the solution through which the current passes leads to an increase in the active resistance of the solution. The relative influence of the double layer capacitance is reduced compared to the converter, in which the area of the electrodes and the effective cross section of the solution are the same.
To reduce the effect on the accuracy of measuring the electrical conductivity of solutions of electrode polarization, four-electrode converters are used, for example, in conductometric analyzers for pure aqueous solutions, type converters with a measurement range are used. Two electrodes of this transducer are current, fed by alternating current voltage through a large limiting resistance, and the other two, located between them, are potential. In this case, the voltage measured at the potential electrodes uniquely determines the concentration of the controlled solution and does not depend on the partial polarization of the current electrodes.
Rice. 22-2-6. circuit diagram electrode transducer with temperature compensation.
Methods of temperature compensation and typical measuring circuits of conductometric analyzers. Temperature compensation is carried out using additional elements in the circuit of the electrode transducer or in the measuring circuit of the liquid conductometer, which reduce the influence of the deviation of the solution temperature from 20 ° C on the instrument readings. Automatic temperature compensation does not completely eliminate the influence of the solution temperature on the instrument readings, which presents great difficulties, but significantly reduces it.
Of the methods used for automatic temperature compensation in liquid conductometers, the most commonly used is an electrode transducer with temperature compensation, the circuit of which is shown in Fig. 22-2-6. The temperature compensation circuit of the electrode transducer is formed by resistors connected in parallel and in series with the resistance of the solution. The resistance of the solution with the resistor has a negative, and the resistor connected in series has a positive temperature coefficient of electrical resistance. The resistor is made of manganin wire, and the resistor is made of copper wire. Nickel or platinum wire is sometimes used to make a resistor. A resistor, performed similarly to the sensing element of a resistance thermometer, is placed in the internal
transducer electrode (Fig. 22-2-2, a). A resistor connected in parallel with the resistance of the solution linearizes the dependence and at the same time reduces the temperature coefficient of the reduced resistance. This creates more favorable conditions for using a compensating resistor.
Rice. 22-2-7. The dependence of the impedance of the converter circuit on the concentration C for temperatures of 18 and 35 ° C.
The calculation of the parameters of the temperature compensation scheme is usually carried out from the condition of full temperature compensation for two given concentrations and certain temperatures selected taking into account possible deviations of the solution temperature from this case, concentration (electrical conductivity) measurements must be made in the range from to, since the error when the temperature of the solution changes beyond the boundaries this interval may be larger than inside it (Fig. 22-2-7).
The impedance of the converter circuit relative to terminals A to B (see Fig. 22-2-6) at the concentration of the solution C and its temperature is determined by the expression
Here, as well as in the following equations, the indices indicate to which solution concentration and temperature the quantities under consideration relate (resistance electrical conductivity electrical conductivity). The condition for complete temperature compensation is reduced to the equalities
In the last two expressions, the temperature coefficient of resistance of copper, corresponding to 0 ° C. When calculating the parameters of the temperature compensation circuit, it is taken to measure the electrical conductivity (salinity) of aqueous solutions at low concentrations, the values \u200b\u200bof are the fourth arm of the bridge); asynchronous reversible motor; synchronous motor. Resistors are made of manganin wire. The resistor is used to establish the required range of resistance change when measuring the electrical conductivity of the solution from the initial to the final scale value, which allows using commercially available automatic balanced KSM2 bridges without changing the reochord and amplifier.
Rice. 22-2-8. Schematic diagram of a liquid conductometer using an electrode transducer (Fig. 22-2-2, 6).
The considered bridge measuring circuit of the secondary device of the liquid conductometer can also be used to measure the electrical conductivity of aqueous solutions with an electrode transducer with temperature compensation (see Fig. 22-2-6), if it is connected to the clamps instead of the transducer Liquid conductometers with such an electrode transducer, manufactured by Tulenergo , used at thermal power plants to measure the electrical conductivity of chemically demineralized water. These liquid conductometers use electrode transducers with temperature compensation from 15 to 35°C of flow and immersion types. The instruments have a specific electrical conductivity measurement range from 0.04 to 20°C.
Consider the method of temperature compensation using a thermistor included in the measuring circuit of the automatic
balanced bridge of the liquid conductometer (Fig. 22-2-9). Here, the ED electrode transducer is included in the measuring bridge circuit of the secondary device, as in Fig. 22-2-8. In this case, the reduced resistance of the converter and the thermistor with a shunt included in the adjacent arms of the bridge have a negative temperature coefficient of resistance. It should be noted that for the thermistor, the dependence, as well as for the non-linear
Rice. 22-2-9. Schematic diagram of a liquid conductometer using a thermistor for temperature compensation.
When measuring conductivity, the thermistor is at the same temperature as the sample solution, as it is usually mounted inside the transmitter housing. The accuracy of temperature compensation will be determined by the degree of consistency between the temperature coefficients of the thermistor with the shunt and the reduced resistance of the converter
The considered temperature compensation with the help of a thermistor included in the measuring bridge circuit is used in the applied conductometric liquid analyzers.
Temperature compensation can also be carried out using an additional electrode transducer, which is filled with an aqueous solution having a temperature coefficient of resistance close to the temperature coefficient of the analyzed solution . In this case, the working and compensating converters are included in the adjacent arms of the measuring circuit of the bridge. In this case, the compensating transducer is washed from the outside by the analyzed solution and has the same temperature with it. This method of temperature compensation is not widely used, since the properties of the solution in the compensation converter change over time.
Automatic balanced bridges, designed to work in conjunction with electrode transducers, can be equipped with an additional device for signaling (regulating) the limiting values of the electrical conductivity of aqueous electrolyte solutions.
In addition to the considered liquid analyzers with electrode transducers, a conductometric analyzer is also available.
Accuracy class 5 AK, developed by SKB AP, with a direct current output signal This conductometric analyzer, equipped with a filter filled with brand cation exchanger, is designed to measure the specific electrical conductivity of aqueous solutions at a temperature of 30-40 ° C and the presence of mineral impurities, ammonia and hydrazine. As a secondary device, an automatic milliammeter KSU2 with measurement ranges
Good afternoon!
Tell me, is there any theoretical method for determining the conductivity of water with compounds dissolved in it, if the initial conductivity of water and the exact quantitative content of compounds dissolved in water are known.
Thank you in advance!
An accurate calculation of the specific electrical conductivity is carried out according to special empirical formulas using calibrated solutions of potassium chloride with a known value of the electrical conductivity. The measured value is usually displayed using the Siemens unit of measurement, 1 cm inverse of 1 ohm. Moreover, for salt water, the results of studies are displayed in S/m, and for fresh water - in μS/meter, that is, in microsiemens. Measurement of the electrical conductivity of aqueous solutions gives for distilled water the SEC value from 2 to 5 μS/meter, for atmospheric precipitation the value is from 6 to 30 or more μS/meter, and for fresh river and lake waters in those areas where the air environment is heavily polluted, the SEC value can fluctuate in within 20-80 μS/cm.
For an approximate assessment of the SEC, one can use the empirically found ratio of the dependence of the SEC on the salt content in water (mineralization):
UEP ( µS/cm ) = salt content (mg / l) / 0,65
That is, to determine the SEC (µS/cm), the salt content (water salinity) (mg/l) is divided by a correction factor of 0.65. The value of this coefficient varies depending on the type of water in the range of 0.55-0.75. Sodium chloride solutions conduct current better: the content of NaCl (mg/l) = 0.53 µS/cm or 1 mg/l NaCl provides an electrical conductivity of 1.9 µS/cm.
For an approximate calculation of the SEC by the content of salts in water (mineralization), you can use the following graph (Fig. 1):
Rice. 1. Graph of the dependence of the SEC on the content of salts in the water (mineralization).
UEC is also measured using a special device - a conductometer, consisting of platinum or steel electrodes immersed in water, through which an alternating current with a frequency of 50 Hz (in low-mineralized water) to 2000 Hz or more (in salt water) is passed, by measuring the electrical resistance .
The principle of operation of the conductometer is based on the direct dependence of the electrical conductivity of water (current strength in a constant electric field created by the electrodes of the device) on the number of compounds dissolved in water. A wide range of suitable equipment now allows you to measure the conductivity of almost any water, from ultrapure (very low conductivity) to saturated chemical compounds(high conductivity).
A conductometer can even be purchased at pet stores, and combinations of such a device with a pH meter are possible. In addition, such a device can be purchased at offices and companies selling equipment for environmental research www.tdsmeter.ru/com100.html.
Craftsmen who are good at using a soldering iron can themselves make a device for measuring electrical conductivity designed by I.I. Vanyushin. (Journal "Fishery", 1990, No. 5, pp. 66-67. In addition, this device and methods for its calibration are described in all details in a very useful book "Modern Aquarium and Chemistry", authors I.G. Khomchenko , A.V. Trifonov, B.N. Razuvaev, Moscow, 1997). The device is made on a common K157UD2 chip, which consists of two operational amplifiers. On the first one, an alternating current generator is assembled, on the second, an amplifier according to a standard scheme, from which readings are taken with a digital or analog voltmeter (Fig. 2).
Rice. 2. Homemade conductometer.
To eliminate the influence of temperature, electrical conductivity measurements are made at a constant temperature of 20 0 C, since the electrical conductivity value and the measurement result depend on temperature, as soon as the temperature rises by at least 1 0 C, the measured electrical conductivity also increases by approximately 2%. Most often, it is recalculated in relation to 20 0 С according to the correction table, or brought to it using empirical formulas.
Correction table for calculating UEP.
Temperature, °C | Correction factor | Temperature, °C | Correction factor | Temperature, °C | Correction factor |
The calculation of the specific electrical conductivity of water in this case is carried out according to the formula :
SEC \u003d C p / R
where C p is the capacitance of the sensor of the device, depending on the material and dimensions of the electrodes and having the dimension cm-1, is determined when the device is calibrated for solutions of potassium chloride with a known value of electrical conductivity; K - temperature coefficient for bringing the measured value at any temperature to its accepted constant value; R - measured electrical resistance of water by the device, in ohms.
The device must be calibrated in resistance values. The following resistances can be recommended for calibration: 1 kOhm (conductivity 1000 µS), 4 kOhm (250 µS), 10 kOhm (100 µS).
In order to more accurately determine the electrical conductivity, you need to know the constant of the vessel for measuring CX. To do this, prepare a 0.01 M solution of potassium chloride (KCl) and measure its electrical resistance R KCl , (in kOhm) in the prepared cell. The capacity of the vessel is determined by the formula:
C p \u003d R KC UEP KCl
where SEC KC is the electrical conductivity of a 0.01M KCl solution at a given temperature in µS/cm, found from the correction table.
After that, the UEP is calculated according to the formula:
UEP = C P (K T ) / R
where C p is the capacitance of the sensor of the device, depending on the material and size of the electrodes and having the dimension of cm -1, is determined by calibrating the device for solutions of potassium chloride with a known value of the SEC; K t - temperature coefficient to bring the measured value at any temperature to its accepted constant value; R - measured electrical resistance of water by the device, in ohms.
The SEC of salt water is usually expressed in Sm/m (Sm is Siemens, the reciprocal of Ohm), fresh water is expressed in microsiemens (µS/cm). SEC of distilled water is 2-5 µS/cm, atmospheric precipitation - from 6 to 30 µS/cm and more, in areas with heavily polluted air, river and fresh lake waters 20-800 µS/cm.
The normalized mineralization values approximately correspond to the specific electrical conductivity of 2 mS / cm (1000 mg / dm 3) and 3 mS / cm (1500 mg / dm 3) in the case of both chloride (in terms of NaCl) and carbonate (in terms of CaCO 3 ). mineralization.
Pure water, as a result of its own dissociation, has an electrical conductivity at 25 C equal to 5.483 µS/m.
For more information about the methods of calculating the UEP, see the relevant sections of our website.
Ph.D. O.V. Mosin
Below are methodical methods for calculating the total mineralization, ionic strength, hardness and determining the content of sulfate ions in natural and Wastewater ax in terms of specific electrical conductivity as a generalized indicator of their quality.
Determining the electrical conductivity (L) of water is reduced to measuring its reciprocal value - the resistance (R), which water renders to the current flowing through it. Thus, L \u003d 1: R, and therefore the electrical conductivity value is expressed in reciprocal Ohms, and according to the modern SI classification - in Siemens (Sm).
The electrical conductivity value remains unchanged within the permissible error (10%) in the presence of organic compounds of various nature (up to 150 mg/dm3) and suspended solids (up to 500 mg/dm3) in natural and waste waters.
To measure specific electrical conductivity (xi), any conductometer with a range from 1*10(-6) S/cm to 10*10(-2) S/cm can be used.
1. OBTAINING AND QUALITY CONTROL OF DISTILLED WATER
1.1. QUALITY STANDARDS
In laboratories for quality control of natural and waste water, distilled water is the main solvent for the preparation of reagents, a diluent for test samples, an extractant, and is also used for rinsing laboratory glassware. Therefore, for the successful operation of any chemical analytical laboratory, along with the fulfillment of such conditions as high qualification of specialists, the availability of accurate verified instruments, the use of reagents of the required degree of purity, standard samples and standard measuring utensils, much attention should be paid to the quality of distilled water, which, in terms of its physico-chemical parameters, must comply with the requirements of GOST 670972 (see table).
REGULATIONS
QUALITY OF DISTILLED WATER BY
pH ¦ 5.4-6.6 ¦
Substances that reduce KMnO4 ¦ 0.08 ¦
Residue after evaporation ¦ 5.0 ¦
Residue after calcination ¦ 1.0 ¦
Ammonia and ammonium salts ¦ 0.02 ¦
Nitrates ¦ 0.20 ¦
Sulphates ¦ 0.50 ¦
Chlorides ¦ 0.02 ¦
Aluminum ¦ 0.05 ¦
Iron ¦ 0.05 ¦
Calcium ¦ 0.80 ¦
Copper ¦ 0.02 ¦
Lead ¦ 0.05 ¦
Zinc ¦ 0.20 ¦
Specific electrical conductivity at 20 deg. C no more than 5*10(-6)cm/cm
If all indicators comply with the established standards, then distilled water is suitable for use in laboratory research, and its quality will not affect the metrological characteristics of analyzes performed in the laboratory. Standards for the frequency of distilled water quality control have not been established.
1.2. RECEIVING AND QUALITY CONTROL
Distilled water is obtained in distillers of various brands. The distiller is installed in a separate room, the air of which should not contain substances that are easily absorbed by water (ammonia vapor, of hydrochloric acid and etc.). At the initial start-up or when the distiller is started after a long-term conservation, the use of distilled water is allowed only after 40 hours of distiller operation and after checking the quality of the resulting water in accordance with the requirements of GOST.
Depending on the composition of the source water, distilled water of various qualities can be obtained.
With a high content of calcium and magnesium salts in water, scale forms on the surface of the heating elements, the inner walls of the steam generator and the refrigeration chamber, as a result of which the heat exchange conditions worsen, leading to a decrease in productivity and a reduction in the life of the distiller. In order to soften the source water and reduce the formation of scale, it is advisable to operate the device in combination with an anti-scale magnetic device or a chemical water conditioner (based on ion-exchange resins in sodium form), for example, grade KU-2-8chs.
The issue of the timing of periodic preventive washing of the distiller and descaling is decided empirically, guided by the data on the quality of distilled water during periodic monitoring. After cleaning and washing the distiller, distilled water is again analyzed for all indicators in accordance with GOST.
All results of water analyzes should be recorded in a log, where at the same time it is necessary to reflect the operating mode of the distiller. The analysis of the obtained results will allow to establish for each source water its own mode of operation of the apparatus: the period of operation, the period of its shutdown for preventive cleaning, washing, rinsing, etc.
If water with a high content of organic matter, then some of them can pass with distillation into distillate and increase the control value of oxidizability. Therefore, GOST provides for the determination of the content of organic substances that reduce potassium permanganate.
To free the distilled water from organic impurities and improve the quality of the distillate, it is recommended to use chemical water conditioners with a granular sorbent from birch activated carbon or with a macroporous granular anion exchanger brand AV-17-10P.
If substances are found in distilled water that reduce potassium permanganate at a concentration of more than 0.08 mg / dm3, it is necessary to carry out a secondary distillation of the distillate with the addition of a solution of 1% KMnO4 to it before distillation, at the rate of 2.5 cm3 per 1 dm3 of water. The total time spent on monitoring the quality of distilled water for all 14 indicators indicated in the table is 11 hours of the analyst's working time (65 laboratory units). Determination of the specific electrical conductivity of water compares favorably in terms of time costs with traditional chemical analysis in determining individual indicators, because the time spent on its determination is no more than 1 laboratory unit (10 minutes) and is recommended as an express method for quality control of distilled water.
By the value of the specific electrical conductivity, it is possible to characterize in general the entire sum of the components of the residual amount minerals(including nitrates, sulfates, chlorides, aluminum, iron, copper, ammonia, calcium, zinc, lead).
If it is necessary to obtain express information about the content of sulfate ions in water, the latter can be calculated from the value of the specific electrical conductivity and the content of hydrocarbonate and chloride ions (see Section 2).
According to GOST, the result of the intention of the value of distilled water is expressed at 20 degrees. FROM
1.3. STORAGE CONDITIONS
Distilled water for laboratory research should be freshly distilled. If necessary, water can be stored in hermetically sealed polyethylene or fluoroplastic bottles. To prevent the absorption of carbon dioxide from the air, bottles with distilled water should be closed with stoppers with calcium chloride tubes. Ammonia-free water is stored in a bottle, closed with a cork with a "goose" containing a solution of sulfuric acid.
3. SETTING THE VALUE OF TOTAL WATER MINERALIZATION
3.1. NATURAL WATERS
One of the most important indicators of water quality is the value of total mineralization, usually determined gravimetrically from the dry residue. Using the data of chemical analysis on the content of chloride, hydrocarbonate and sulfate ions, using conversion factors, you can calculate the value of the total mineralization (M, mg / dm3) of the water under study according to the formula (2):
M=[HCO(3-)*80+[Cl-]-55+*67
where [НСО(3-)], [Сl], are the concentrations of bicarbonate, chloride, sulfate ions in mg-eq / dm.cub. respectively. The numerical factors approximately correspond to the arithmetic mean of the molar mass equivalents of the salts of the corresponding anion with calcium, magnesium, sodium, and potassium.
3. METHOD FOR ASSESSING THE IONIC STRENGTH OF AQUEOUS SOLUTION
In the practice of hydrochemical studies, the value of the ionic strength of water is used to control the ionic composition of water using ion-selective electrodes, as well as in the express calculation of the total hardness.
Calculation of the ionic strength (mu) of natural and waste water is carried out on the basis of the results of a double measurement of the specific electrical conductivity of water: undiluted (xi1) and diluted in a ratio of 1:1 (xi2).
Ionic strength is calculated using formula (4):
(mu)=K*Sm10 (4)
Where Cm is the total mineralization of water, calculated from the value of the specific electrical conductivity as a * 10 (4) and expressed in mg-eq / dm3;
K - ionic indicator, set using a correction table for the values of Cm and xi2 / xi1.
The values (mu) calculated by this method of natural and waste waters (even containing a large number of suspended particles) are consistent with the values (mu) determined from the data of chemical analysis of the content of the main ions; the discrepancy between the results of the two methods does not exceed 10%, which is consistent with the permissible reproducibility standards.
This express method for determining the ionic strength of natural and waste waters is more economical and has an advantage in the control of turbid and colored waters.
4. METHOD FOR ASSESSING TOTAL WATER HARDNESS
Displacement hardness is one of the most important group indicators of water quality for all types of water use. The generally accepted complex-metric determination of hardness has a significant limitation and cannot be used in the analysis of turbid and colored waters, as well as with a significant content of a number of metals. When determining the general hardness, such waters must be subjected to special treatment, which is associated with an increase in the consumption of chemical reagents and additional costs of working time for analysis.
An accelerated method for estimating the approximate value of the total hardness (W total) is based on the data obtained from the results of measuring the electrical conductivity. The calculation is made according to the formula (5)%
W total = 2(mu) * 10(3) - (2cm + SO4(2-)]) (5)
where (mu) is the ionic strength of water (calculated from electrical conductivity data, see Section 4); Cm - total mineralization, mg-eq / dm.cub. (calculated from conductivity data, see section 4); - concentration of sulfate ions, mg-eq / dm.cub. (calculated from conductivity data, see section 2, or another method). The error in determining the stiffness in this way is within acceptable limits (5% ). The method is recommended as an accelerated method for assessing the overall hardness in the conditions of mass analysis of samples in the environmental monitoring system, especially in the case of turbid, colored waters and waters heavily contaminated with ions of a number of heavy metals.
LITERATURE
GOST 6709-72 "Distilled water".
Instructions on the organization and structure of laboratory control in the system of the Ministry of Housing and Communal Services of the RSFSR. M. 1986.
Vorobyov I.I. Application of conductivity measurement for characterization chemical composition natural waters. M., Publishing House of the Academy of Sciences of the USSR, 1963-141 p.
Pochkin Yu.N. Determination of the electrical conductivity of water in the study of the salt regime of open reservoirs // Hygiene and Sanitation. 1967, No. 5.
GOST 17403-72. Hydrochemistry. Basic concepts. Terms and Definitions.
Lurie Yu.Yu. Analytical chemistry of industrial wastewater. M., Chemistry, 1984.-447 p.
RD 52.24.58-88. Method for measuring the content of sulfate ions by the titrimetric method with a barium salt.
RD 52.24.53-88. Method for measuring the content of sulfate ions with a lead salt.
GOST 27384-87. Water. Measurement error rates are indicative of the composition and properties.
GOST 26449.1-85. Stationary distillation desalination plants. Methods of chemical analysis of salt waters.
Information leaflet N 29-83. Determination of boiler water content. TsNTI, Arkhangelsk. 1983.
Guide chemical analysis land surface waters. L., Gidrometeoizdat. 1977. - 537 p.
Accelerated determination of total mineralization, total hardness, ionic strength, sulfate ion content and free CO2 by electrical conductivity. Kazan. GIDUV. 1989. - 20 p.
MINISTRY OF EDUCATION AND SCIENCE
RUSSIAN FEDERATION
FEDERAL AGENCY FOR EDUCATION
State educational institution
"KAZAN STATE
ENERGY UNIVERSITY»
DETERMINATION OF THE SPECIFIC CONDUCTIVITY OF WATER USING THE PWT CONDUCTOMETER Hanna Instruments
Laboratory work on the course
(4 hours)
"Environmental audit in the energy sector
and industry"
Kazan
2010
Determination of the electrical conductivity of water using a PWT conductivity meter Hanna Instruments
Objective
1. Get acquainted with the device and principle of operation of the PWT Hanna Instruments conductometer.
2. Learn to determine the electrical conductivity of water by conductometry, using a PWT Hanna Instruments conductometer.
3. Get acquainted with the device and principle of operation of the distiller and bidistillator, study the change in the electrical conductivity of water before and after distillation.
Work task
1. Get to know the working principle of PWT Hanna Instruments Conductivity Meter;
2. Get acquainted with the device and the principle of operation of the distiller;
3. See the measurement of the electrical conductivity of water before and after distillation;
4. Describe the progress of the work;
5. Issue a protocol of measurement results;
6. Answer security questions.
Equipment and reagents
1. Conductometer PWT Hanna Instruments;
2. distiller;
3. bidistillator;
4. beakers with a capacity of 150-200 ml.
Theoretical part
General information
Electrical conductivity- is the ability of an aqueous solution to conduct an electric current, expressed in numerical form. Electrical conductivity natural water depends on the degree of mineralization (concentration of dissolved mineral salts) and temperature. Therefore, the magnitude of the electrical conductivity of water can be used to judge the degree of mineralization of water. Natural water is a solution of mixtures of strong and weak electrolytes. The mineral part of the water consists of sodium (Na+), potassium (K+), calcium (Ca2+), chlorine (Cl-), sulfate (SO42-), hydrocarbonate (HCO3-) ions. It is these ions that determine the electrical conductivity of natural waters. The electrical conductivity depends on: the concentration of ions, the nature of the ions, the temperature of the solution, the viscosity of the solution.
Pure water, as a result of its own dissociation, has an electrical conductivity at 25 C equal to 5.483 µS/m.
Methods for measuring the electrical conductivity of water
To determine the electrical conductivity of water, the conductometric method is usually used.
Conductometry- (from English conductivity - electrical conductivity and Greek metreo - I measure), an electrochemical method for analyzing solutions of chemicals and natural waters, based on measuring their electrical conductivity. The principle of conductometric analysis is a change in the chemical composition of the medium or the concentration of a certain substance in the interelectronic space. The advantages of conductometry include: high sensitivity, sufficiently high accuracy, simplicity of methods, availability of equipment, the possibility of studying colored and turbid solutions, as well as automating the analysis. To measure the electrical conductivity of aqueous solutions, melts, colloidal systems, a special device is used - conductometer.
Fields of application for conductometry
Conductometers are used to control the SEC of liquid media in technological processes chemical, petrochemical industries, energy facilities (thermal power plants, nuclear power plants), where the electrical properties of liquids characterize product quality.
Evaluation of the quality of distilled water by specific electrical conductivity is a textbook operation. Distilled water should have an electrical conductivity of no more than 10-6 Sim (om-1).
Description of PWT Conductometer Hanna Instruments
Conductometer PWT Hanna Instruments - a device designed for rapid determination of the electrical conductivity of water. It can be used both in laboratories and in the field. The main features of the device: manual one-point calibration, automatic thermal compensation. Electrical conductivity measurements are carried out using an OK-102 conductometer, which allows you to immediately determine the values of electrical conductivity in Siemens.
Drinking water "href="/text/category/voda_pitmzevaya/" rel="bookmark"> purified water from mineral salts, organic substances, ammonia, carbon dioxide and other impurities dissolved in it. It is obtained by distillation in special apparatus - distillers.
In this laboratory work, a DE-4 distiller and a PURATOR-MONO bidistiller are used to obtain distilled water.
Progress
Pour tap water into a 150-200 ml beaker. Turn on the conductometer and place it in the test volume, record the measurement result in the protocol.
Pour the water obtained with the DE-4 distiller into a 150-200 ml beaker. Turn on the conductometer and place it in the test volume, record the measurement result in the protocol. Repeat the operation with water obtained with a bidistillator.
Measurement protocol
test questions
1. What determines the electrical conductivity of water?
2. What methods for determining the specific electrical conductivity of water do you know?
3. What instrument is used to determine the electrical conductivity of water?
5. Name the scope of conductometry.
6. How is distilled water obtained?
Specific electrical conductivity (specific electrical conductivity)
- a quantitative characteristic of the ability of water to conduct electric current.
This ability is directly related to the concentration of ions in water. Conductive ions come from dissolved salts and inorganic materials such as alkalis, chlorides, sulfides and carbonate compounds, etc. The more ions present, the higher the conductivity of water.
Ions conduct electricity due to their positive and negative charges. When substances dissolve in water, they split into positively charged (cationic) and negatively charged (anionic) particles. When solutes are broken down in water, the concentrations of each positive and negative charge remain equal. This means that although the conductivity of water increases with the added ions, it remains electrically neutral.
In most cases, the specific electrical conductivity of land surface waters is an approximate characteristic of the concentration of inorganic electrolytes in water - Na cations+ , K + , Ca 2+ , Mg 2+ and anions Сlˉ, SO 4 2- , HCO 3 - . The presence of other ions, for example Fe (II), Fe (III), Mn (II), NO 3 - , HPO 4 2- usually has little effect on the electrical conductivity, since these ions are rarely found in water in significant quantities. Hydrogen and hydroxide ions in the range of their usual concentrations in land surface waters practically do not affect the electrical conductivity. The effect of dissolved gases is just as small.
Conductivity can be measured by applying an alternating electrical current (I) to two electrodes immersed in a solution and measuring the resulting voltage (V). During this process, cations migrate to the negative electrode, anions to the positive electrode, and the solution acts as an electrical conductor. The voltage is used to measure the resistance of the water, which is then converted to conductance. Conductivity is the reciprocal of resistance and is measured as the amount of conduction at a given distance.
The unit of electrical conductivity is Siemens per 1 m (S/m).For water, the unit of measurement is derived values - milliSimmens per 1 m (mS/m) or microSiemens per 1 cm (µS/cm). For very pure water It is inconvenient to operate with the conductivity value, therefore, the term resistivity, measured in Ohm / m (KOhm / cm or MΩ / cm), is more often used. So, for example, pThe conductivity of rivers can range from 50 to 1500 µS/cm, ddistilled water has a conductivity in the range of 0.5 to 5 μS/cm, ultrapure deionized water 10-18 MΩ/cm.
Conductivity in streams and rivers is primarily dependent on the geology of the area through which the water flows. Streams flowing through areas with granite rock tend to decrease in conductivity because granite is composed of more inert materials that do not ionize (dissolve in ionic components) when washed in water. On the other hand, streams flowing through areas with clay soils tend to be more conductive due to the presence of materials that are ionized when washed in water. Groundwater inflows can have the same effects depending on which they flow through. Discharges into rivers can change conductivity depending on their composition. Faulty sewer system will increase conductivity due to the presence of chloride, phosphate and nitrate; oil spill will reduce conductivity.
The conductivity of water must be accurately measured using a calibrated instrument - a conductometer. The conductivity is directly affected by the geometric properties of the electrodes; that is, the conductivity is inversely proportional to the distance between the electrodes and proportional to the area of the electrodes. This geometric relationship is known as the cell constant. Cell constant and resistance measurement to be checked and adjusted if necessary.
In addition to the geometric properties of the electrode in the device, and conductivity is also affected by temperature: the warmer the water, the higher the conductivity. For this reason, electrical conductivity is reported as conductivity at 25 degrees Celsius (25 °C).An increase in the temperature of the solution will lead to a decrease in its viscosity and an increase in the mobility of ions in the solution. An increase in temperature can also lead to an increase in the number of ions in solution due to the dissociation of molecules. Since the conductivity of a solution depends on these factors, an increase in the temperature of the solution will lead to an increase in its conductivity. Knowing this dependencymany instruments automatically correct the actual reading to display the value that would theoretically be observed at a nominal temperature of 25°. This is usually done using a temperature sensor built into the conductivity probe and a software algorithm built into the conductivity meter. However, forlinear temperature compensation assumes that the temperature coefficient of variation has the same value for all measurement temperatures. This assumption is wrong; but for many measurements this does not contribute significantly to the total measurement uncertainty of the reported result.
http://www.iwinst.org/wp-content/uploads/2012/04/Conductivity-what-is-it.pdfhttps://hmc.usp.org/sites/default/files/documents/HMC/GCs-Pdfs/c645.pdf
https://www.google.ru/urlsa=t&rct=j&q=&esrc=s&source=web&cd=3&ved=0ahUKEwjR9Kautv_WAhVFP5oKHRb4D3MQFgg7MAI&url=http%3A%2F%2Fwww.fondriest.com%2Fenvironmental-measurements%2Fparameters%2Fwater-quality%2Fconductivity- salinity-tds%2F&usg=AOvVaw31-HAReIg1Tn1CDOmaAVim
The Clean Water Team Guidance Compendium for Watershed Monitoring and Assessment State Water Resources Control Board FS-3.1.3.0(EC)V2e 4/27/2004
https://www.reagecon.com/pdf/technicalpapers/Effect_of_Temperature_TSP-07_Issue3.pdf
RD 52.24.495-2005 Hydrogen index and electrical conductivity of water. Method for performing measurements by the electrometric method
Who knows the formula of water since school days? Of course, everything. It is likely that from the entire course of chemistry, for many who then do not study it specializedly, only the knowledge of what the formula H 2 O stands for is left. But now we will try to figure out in as much detail and depth as possible what are its main properties and why life without it on planet Earth is not possible.
Water as a substance
The water molecule, as we know, consists of one oxygen atom and two hydrogen atoms. Its formula is written as follows: H 2 O. This substance can have three states: solid - in the form of ice, gaseous - in the form of steam, and liquid - as a substance without color, taste and smell. By the way, this is the only substance on the planet that can exist in all three states simultaneously in natural conditions. For example: at the poles of the Earth - ice, in the oceans - water, and evaporation under the sun's rays is steam. In this sense, water is anomalous.
Water is also the most common substance on our planet. It covers the surface of planet Earth by almost seventy percent - these are oceans, and numerous rivers with lakes, and glaciers. Most of the water on the planet is salty. It is unsuitable for drinking and for doing Agriculture. Fresh water makes up only two and a half percent of the total amount of water on the planet.
Water is a very strong and high-quality solvent. Due to this, chemical reactions in water take place at a tremendous speed. This same property affects the metabolism in the human body. that the body of an adult is seventy percent water. In a child, this percentage is even higher. By old age, this figure drops from seventy to sixty percent. By the way, this feature of water clearly demonstrates that it is the basis of human life. The more water in the body - the healthier, more active and younger it is. Therefore, scientists and doctors of all countries tirelessly repeat that you need to drink a lot. It is water in its pure form, and not substitutes in the form of tea, coffee or other drinks.
Water forms the climate on the planet, and this is not an exaggeration. Warm currents in the ocean heat entire continents. This is due to the fact that water absorbs a lot of solar heat, and then gives it away when it starts to cool. So it regulates the temperature on the planet. Many scientists say that the Earth would have cooled down and turned into stone long ago if it weren’t for the presence of so much water on the green planet.
Water properties
Water has many very interesting properties.
For example, water is the most mobile substance after air. From the school course, many, for sure, remember such a thing as the water cycle in nature. For example: a stream evaporates under the influence of direct sunlight, turns into water vapor. Further, this steam is carried somewhere by the wind, collects in clouds, and even falls in the mountains in the form of snow, hail or rain. Further, from the mountains, the brook again runs down, partially evaporating. And so - in a circle - the cycle is repeated millions of times.
Water also has a very high heat capacity. It is because of this that water bodies, especially oceans, cool very slowly during the transition from a warm season or time of day to a cold one. Conversely, when the air temperature rises, the water heats up very slowly. Due to this, as mentioned above, water stabilizes the air temperature throughout our planet.
After mercury, water has the highest surface tension. It is impossible not to notice that a drop accidentally spilled on a flat surface sometimes becomes an impressive speck. This shows the ductility of water. Another property manifests itself when the temperature drops to four degrees. As soon as the water cools to this mark, it becomes lighter. Therefore, ice always floats on the surface of the water and freezes in a crust, covering rivers and lakes. Thanks to this, in ponds that freeze in winter, fish do not freeze out.
Water as a conductor of electricity
First, you should learn about what electrical conductivity is (including water). Electrical conductivity is the ability of a substance to conduct an electric current through itself. Accordingly, the electrical conductivity of water is the ability of water to conduct current. This ability directly depends on the amount of salts and other impurities in the liquid. For example, the electrical conductivity of distilled water is almost minimized due to the fact that such water is purified from various additives that are so necessary for good electrical conductivity. An excellent current conductor is sea water, where the concentration of salts is very high. The electrical conductivity also depends on the temperature of the water. The higher the temperature, the greater the electrical conductivity of water. This regularity was revealed thanks to multiple experiments of physicists.
Water conductivity measurement
There is such a term - conductometry. This is the name of one of the methods of electrochemical analysis based on the electrical conductivity of solutions. This method is used to determine the concentration in solutions of salts or acids, as well as to control the composition of some industrial solutions. Water has amphoteric properties. That is, depending on the conditions, it is able to exhibit both acidic and basic properties - to act both as an acid and as a base.
The instrument used for this analysis has a very similar name - a conductometer. Using a conductometer, the electrical conductivity of electrolytes in a solution is measured, the analysis of which is being carried out. Perhaps it is worth explaining another term - electrolyte. This is a substance that, when dissolved or melted, decomposes into ions, due to which an electric current is subsequently conducted. An ion is an electrically charged particle. Actually, the conductometer, taking as a basis certain units of electrical conductivity of water, determines its electrical conductivity. That is, it determines the electrical conductivity of a specific volume of water, taken as the initial unit.
Even before the beginning of the seventies of the last century, the unit of measure "mo" was used to indicate the conductivity of electricity, it was a derivative of another quantity - Ohm, which is the main unit of resistance. Electrical conductivity is a quantity that is inversely proportional to resistance. Now it is measured in Siemens. This value got its name in honor of the physicist from Germany - Werner von Siemens.
Siemens
Siemens (it can be denoted by both Cm and S) is the reciprocal of Ohm, which is a unit of measurement of electrical conductivity. One cm is equal to any conductor whose resistance is 1 ohm. Siemens is expressed through the formula:
- 1 Sm \u003d 1: Ohm \u003d A: B \u003d kg −1 m −2 s³A², where
A - ampere,
V - volt.
Thermal conductivity of water
Now let's talk about - this is the ability of a substance to transfer thermal energy. The essence of the phenomenon lies in the fact that the kinetic energy of atoms and molecules, which determine the temperature of a given body or substance, is transferred to another body or substance during their interaction. In other words, thermal conductivity is heat exchange between bodies, substances, as well as between a body and a substance.
The thermal conductivity of water is also very high. People daily use this property of water without noticing it. For example, pouring cold water into a container and cooling drinks or foods in it. Cold water takes heat from the bottle, container, instead of giving cold, the reverse reaction is also possible.
Now the same phenomenon can be easily imagined on a planetary scale. The ocean heats up during the summer, and then - with the onset of cold weather, it slowly cools down and gives up its heat to the air, thereby heating the continents. Having cooled down during the winter, the ocean begins to warm up very slowly compared to the land and gives up its coolness to the continents languishing from the summer sun.
Density of water
It was said above that fish live in a reservoir in winter due to the fact that water freezes with a crust over their entire surface. We know that water begins to turn into ice at a temperature of zero degrees. Due to the fact that the density of water is greater than the density floats and freezes on the surface.
water properties
Also, water under different conditions can be both an oxidizing agent and a reducing agent. That is, water, giving up its electrons, is positively charged and oxidized. Or it acquires electrons and is charged negatively, which means it is restored. In the first case, the water oxidizes and is called dead. It has very powerful bactericidal properties, but you don’t need to drink it. In the second case, the water is alive. It invigorates, stimulates the body to recover, brings energy to the cells. The difference between these two properties of water is expressed in the term "redox potential".
What can water react with?
Water is able to react with almost all substances that exist on Earth. The only thing is that for the occurrence of these reactions, it is necessary to provide a suitable temperature and microclimate.
For example, at room temperature, water reacts well with metals such as sodium, potassium, barium - they are called active. Halogens are fluorine and chlorine. When heated, water reacts well with iron, magnesium, coal, methane.
With the help of various catalysts, water reacts with amides, esters of carboxylic acids. A catalyst is a substance that seems to push the components to a mutual reaction, accelerating it.
Is there water anywhere else but Earth?
So far, water has not been found on any planet in the solar system, except for the Earth. Yes, they assume its presence on the satellites of such giant planets as Jupiter, Saturn, Neptune and Uranus, but so far scientists do not have exact data. There is another hypothesis, not yet fully verified, about groundwater on the planet Mars and on the Earth's satellite - the Moon. Regarding Mars, a number of theories have been put forward that once there was an ocean on this planet, and its possible model was even designed by scientists.
Outside the solar system, there are many large and small planets, where, according to scientists, there may be water. But so far there is not the slightest way to be sure of this for sure.
How to use the thermal and electrical conductivity of water for practical purposes
Due to the fact that water has a high heat capacity, it is used in heating mains as a heat carrier. It provides heat transfer from the producer to the consumer. Many nuclear power plants also use water as an excellent coolant.
In medicine, ice is used for cooling, and steam for disinfection. Ice is also used in the catering system.
In many nuclear reactors, water is used as a moderator for the success of a nuclear chain reaction.
Pressurized water is used to split, break through and even cut rocks. This is actively used in the construction of tunnels, underground facilities, warehouses, subways.
Conclusion
It follows from the article that water, in terms of its properties and functions, is the most irreplaceable and amazing substance on Earth. Does the life of a person or any other living being on Earth depend on water? Certainly yes. Does this substance contribute to human scientific activity? Yes. Does water have electrical conductivity, thermal conductivity and other useful properties? The answer is also yes. Another thing is that there is less and less water on Earth, and even more so clean water. And our task is to preserve and protect it (and, therefore, all of us) from extinction.