CN106645268B - Freezing point measuring device - Google Patents
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- CN106645268B CN106645268B CN201710089983.4A CN201710089983A CN106645268B CN 106645268 B CN106645268 B CN 106645268B CN 201710089983 A CN201710089983 A CN 201710089983A CN 106645268 B CN106645268 B CN 106645268B
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- G01N25/00—Investigating or analyzing materials by the use of thermal means
- G01N25/02—Investigating or analyzing materials by the use of thermal means by investigating changes of state or changes of phase; by investigating sintering
- G01N25/04—Investigating or analyzing materials by the use of thermal means by investigating changes of state or changes of phase; by investigating sintering of melting point; of freezing point; of softening point
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Abstract
The freezing point measuring device comprises an ice bath device, a refrigerating device and a cold trap for placing the ice bath, wherein the ice bath device comprises an ice bath, a measuring pipe stirring rod inserted into the measuring pipe and an ice bath stirring rod inserted into the ice bath, the measuring pipe is outwards communicated with a feeding branch pipe which is inclined upwards, the feeding branch pipe is arranged between an air sleeve plug and an upper cover of the measuring pipe, and the top end of the feeding branch pipe is provided with a branch pipe plug for sealing the feeding branch pipe; the refrigerating device comprises a compressor, a condenser, a capillary tube and a coiled evaporator, wherein the compressor, the condenser, the capillary tube and the coiled evaporator are connected in turn through a refrigerant pipeline in a circulating manner; the invention also discloses a method for measuring the freezing point by using the freezing point measuring device, which can conveniently control the experiment temperature and the stirring speed and avoid the serious supercooling phenomenon.
Description
Technical Field
The invention belongs to the technical field of thermal analysis, and relates to a freezing point measuring device.
Background
The freezing point is an important physicochemical parameter of the substance, and the determination of the freezing point of the substance has important significance. The molecular weight, i.e., molar mass, of the solute can also be calculated using the freezing point measurements of the solvent and solution.
The freezing point depression method for measuring the molecular weight of a substance is one of the classical methods for measuring the molecular weight of a substance. The principle is based on the colligative property of the dilute solution, namely, the use range of the freezing point depression method for measuring the molar mass of the solution formed by solute which is non-volatile, non-dissociative, non-polymeric and does not form solid-liquid with the solvent is the dilute solution formed by non-volatile non-electrolyte substances.
For dilute solution containing non-volatile non-electrolyte, and solute molecules are not associated, the freezing point depression value Δ T of the solution is proportional to the molarity of the solution for a certain solvent:
namely:
（1）
in the formula:K f the freezing point depression constant, the value of which varies from solvent to solvent, of waterK f =1.86K ∙kg∙mol -1 ；
b B Mol ∙ kg for molal concentrations -1 。
Wherein
（2）
Substituting (2) into (1) can obtain:
in the formula: m is B -weight of solute (g);
M B molecular weight of solute (g ∙ mol) -1 ）；
m A -weight of solvent (g).
Therefore, a certain weight of solvent and solute are taken to prepare a solution, and the molecular weight can be calculated according to the formula (3) by measuring the freezing point depression value of the solution.
The freezing point determination experiment needs to use a freezing point determination device, the traditional freezing point determination device is to put an ice-salt water mixture into an ice bath, the temperature is basically controlled within the range of-2 to-3 ℃, the temperature control is realized by adjusting the proportion of adding ice salt, during measurement, a large test tube is put into the ice-salt bath, a determination tube filled with a solution to be determined is put into the large test tube, and a manual stirring rod is used for stirring when stirring is needed. The key for influencing the success or failure of the freezing point determination experiment is to control the supercooling degree and the stirring rate, so the traditional experiment method has the following defects: (1) The experiment temperature cannot be conveniently controlled, and the phenomenon that the measured solution is seriously supercooled or is insufficiently refrigerated can be caused, so that the experiment fails and the experiment efficiency is influenced; (2) The manual stirring is not only inconvenient to control the stirring speed, but also can touch the inner wall of the measuring tube and the thermometer in the stirring process, so that the risk of collision and damage is caused.
Disclosure of Invention
The invention provides a freezing point measuring device for overcoming the defects in the prior art, which can conveniently control the experiment temperature and the stirring speed and avoid the serious supercooling phenomenon.
In order to solve the technical problem, the invention adopts the following technical scheme: the freezing point determination device comprises an ice bath device, a refrigeration device and a cold trap for placing the ice bath device, wherein the ice bath device comprises an ice bath tank, a determination pipe stirring rod inserted into the determination pipe and an ice bath tank stirring rod inserted into the ice bath tank,
an ice bath upper cover is arranged at the upper end of the ice bath, the ice bath upper cover is buckled and connected with the ice bath, a large test tube hole and a small test tube hole matched with the measuring tube are formed in the ice bath upper cover, an air sleeve is inserted into the large test tube hole, an air sleeve plug used for sealing the air sleeve is arranged at the upper end of the air sleeve, the measuring tube penetrates through the air sleeve plug and is inserted into the air sleeve, and a gap is formed between the outer wall of the measuring tube and the inner wall of the air sleeve; the upper end of the measuring pipe is provided with an upper measuring pipe cover, the bottom ends of the ice bath tank stirring rod and the measuring pipe stirring rod are respectively provided with an annular stirring part, the measuring pipe is outwards communicated with a feeding branch pipe which is inclined upwards, the feeding branch pipe is arranged between the air sleeve plug and the upper measuring pipe cover, and the top end of the feeding branch pipe is provided with a branch pipe plug used for sealing the feeding branch pipe;
the refrigeration device comprises a compressor, a condenser, a capillary tube and a coiled evaporator, wherein the compressor, the condenser, the capillary tube and the coiled evaporator are circularly connected through a refrigerant pipeline in sequence, the condenser is provided with radiating fins, and the coiled evaporator is coiled around a cold trap;
and a magnetic stirrer is arranged on the lower side of the bottom of the cold trap, and magnetic stirrers corresponding to the magnetic stirrer are respectively arranged on the inner side of the bottom of the ice bath and the bottom of the measuring tube.
The ice bath upper cover and the ice bath groove are buckled and connected by a specific structure that: four side buckles capable of being turned are evenly fixed on the periphery of the upper cover of the ice bath tank, grooves are formed in the side buckles, and four bulges matched with the grooves are arranged on the periphery of the upper end of the ice bath tank.
The digital Beckmann thermometer is connected with a temperature probe, the temperature probe is inserted into the measuring tube through the upper cover of the measuring tube and is sleeved in the annular stirring part at the bottom end of the stirring rod of the measuring tube at intervals, the ice bath temperature sensor is inserted into the ice bath through the upper cover of the ice bath and is sleeved in the annular stirring part at the bottom end of the stirring rod of the ice bath at intervals, the digital Beckmann thermometer and the ice bath temperature sensor are connected with the electric control device through data lines, the electric control device is also connected with the magnetic stirrer and the compressor respectively, and the electric control device is connected with a power switch, a speed regulating button for regulating the stirring speed of the magnetic stirrer and a display screen for displaying the readings of the digital Beckmann thermometer and the ice bath temperature sensor.
A method for determining freezing point using a freezing point measuring device, comprising the steps of:
(1) Preparation of the assay
An operator adds crushed ice, tap water and salt into an ice bath tank, places a magnetic stirrer at the bottom of the ice bath tank, buckles an upper cover of the ice bath tank with the ice bath tank, places the ice bath tank into a cold trap, places an air sleeve into the ice bath tank through a large test tube hole, and opens a refrigeration device and a digital Beckmann thermometer;
an operator inserts an ice bath temperature sensor into an ice bath tank, pulls an ice bath tank stirring rod to stir up and down in the ice bath tank, an electric control device is internally provided with an upper limit value and a lower limit value of the ice bath temperature sensor, the upper limit value is 2 ℃ lower than the theoretical freezing point of a solvent, the lower limit value is 3 ℃ lower than the theoretical freezing point of the solvent, when the temperature measured by the ice bath temperature sensor is lower than the lower limit value, refrigeration equipment is closed, when the temperature is higher than the upper limit value of the temperature range, the refrigeration equipment is started, when the ice bath temperature is maintained to be 2-3 ℃ lower than the theoretical freezing point of distilled water, stirring is stopped, a 'keeping' key 'on a digital Beckman thermometer is pressed, the base temperature is locked, the measuring range is selected, 0 grade is generally selected, the digital Beckman thermometer is a conventional device in the field, the' keeping 'key' is arranged on the digital Beckman thermometer, the measuring range can be selected, and the specific structure of the digital Beckman thermometer is not detailed any more;
an operator accurately transfers 25ml of distilled water into a clean and dry measuring tube by using a pipette, a magnetic stirrer is placed into the measuring tube, a temperature probe of a digital Beckmann thermometer is inserted into an upper cover of the measuring tube, then the upper cover of the measuring tube is closed, the temperature probe is immersed into the distilled water in the measuring tube and is positioned at the central position inside the measuring tube, and the end part of the temperature probe is 5mm away from the bottom of the measuring tube and does not collide with any substance;
(2) Crude determination of the freezing point of the solvent
An operator inserts the measuring tube filled with the solvent into the ice bath from the small test tube hole, adjusts the speed regulating knob to a proper position, observes the indicating value of the digital Beckmann thermometer through the display screen until the indicating value is stable and unchanged, and the indicating value of the digital Beckmann thermometer is the initial measuring solidification point of the pure solvent sample;
(3) Determination of the freezing point of a solvent
An operator takes out the measuring tube, dries the measuring tube, holds the measuring tube with a palm for heating, inserts the measuring tube into the ice bath from the small test tube hole after the ice in the measuring tube is completely melted, quickly takes out the measuring tube when the temperature in the measuring tube is reduced to be 0.7 ℃ higher than the initial measuring freezing point, dries the measuring tube, inserts the measuring tube into the air sleeve, and records the temperature value in the measuring tube in time; the speed regulation knob is adjusted to slowly stir so as to lead the temperature to be uniformly reduced, and the indication value of the digital Beckmann thermometer displayed by the display screen is recorded at intervals of 30 seconds; when the temperature is lower than the initial measurement solidifying point, the speed regulating knob is adjusted in time to accelerate stirring and provide a condensation center to separate out solids, and when the temperature rises back to be not less than 0.01 ℃, the speed regulating knob is adjusted to slowly stir; when the temperature rises to the temperature which is not changed any more, the temperature lasts for 60 seconds, and the indication value of the digital Beckmann thermometer displayed by the display screen is the freezing point of the distilled water; repeating the step (3) for 2 times, measuring the freezing points of the distilled water for three times, and taking the average value of the freezing points as the final measured freezing point of the distilled water;
(4) Determination of the freezing point of aqueous solutions of sucrose
An operator takes out the measuring tube, wipes the measuring tube dry, holds the measuring tube with a palm for heating, after the measuring tube is frozen and completely melts, 1-1.4 g of accurately weighed cane sugar is put into the measuring tube, after the cane sugar is completely dissolved, the freezing point of the solution is initially measured, the measuring tube of the cane sugar aqueous solution is inserted into an ice bath from a small test tube hole, the speed of a magnetic stirrer is adjusted, a speed regulating knob is adjusted to a proper position, the indication value of a digital Beckmann thermometer is observed through a display screen, the indication value of the display screen is recorded at intervals of 30 seconds, the absolute value of the difference between every two recorded values is recorded as delta t, the difference between every two delta t is less than 0.01 ℃ in the initial stage of inserting the measuring tube filled with the cane sugar aqueous solution into the small test tube hole of the ice bath, the temperature of the cane sugar aqueous solution is reduced at a constant speed due to no solidification of the solvent in the initial stage, when the solidification point of the solvent is reached, the temperature of the solid solvent is separated out, the heat is released, the temperature of the cane sugar aqueous solution is reduced, and the initial value of the last delta t is recorded as the reciprocal of the aqueous solution of the first measured as the first measured screen; then accurately measuring the freezing point of the sucrose aqueous solution, taking out the measuring tube, wiping the measuring tube dry, holding the measuring tube with a palm for heating, inserting the measuring tube into an ice bath from a small test tube hole after the ice in the measuring tube is completely melted, quickly taking out the measuring tube when the temperature is reduced to 0.7 ℃ higher than the initial measuring freezing point, wiping the measuring tube dry, inserting the measuring tube into an air sleeve, and recording the temperature value in the measuring tube at the moment in time; the speed regulation knob is adjusted to stir slowly to enable the temperature to drop uniformly, the indication value of the digital Beckmann thermometer displayed by the display screen is recorded at intervals of 30 seconds, and the absolute value of the difference value between every two recorded values is recorded as delta T; when the temperature is lower than the initial measurement solidification point, adjusting a speed regulation knob in time to accelerate stirring and provide a condensation center to separate out solids, and when the temperature rises to be not less than 0.01 ℃, adjusting the speed regulation knob to slowly stir; when the delta T value of the last time is reduced by more than 0.01 ℃ than the value of the last time, the indication value of the display screen recorded for the penultimate time is taken as the accurate measurement freezing point of the sucrose aqueous solution; repeating the step of accurately measuring the freezing point of the sucrose aqueous solution for 2 times, measuring the freezing points of the sucrose aqueous solutions for three times, and taking the average value of the freezing points as the finally measured freezing point of the sucrose aqueous solution;
when the temperature of the solution is reduced to be below the freezing point of the initial measurement solvent, if no ice is separated out from the sucrose aqueous solution, taking down the branch pipe plug, and putting seed crystals into the measurement pipe from the feeding branch pipe;
(5) The refrigeration equipment and the digital beckmann thermometer were turned off.
By adopting the technical scheme, the invention has the following beneficial effects:
the ice bath upper cover is buckled and connected with the ice bath groove, so that the buckling of the ice bath upper cover is more convenient and firm, the cover can be prevented from rotating during stirring, the sealing performance of the ice bath groove is improved, the internal and external heat exchange is reduced, and the experiment temperature control is facilitated.
The air sleeve pipe enables the measuring pipe to be located in a space with uniform temperature, and the air cooling can slow down the cooling rate and prevent the phenomenon of excessive supercooling. If an air sleeve is not used, the measuring tube is directly inserted into the ice bath, the temperature is reduced too fast, new phases are not easy to generate, a strong supercooling phenomenon is easy to generate, the solvent solidification cannot be formed, and finally the experiment failure is caused.
Throw material branch pipe and can be used to add the seed crystal in survey pipe, compare and directly add the seed crystal in survey pipe, can reduce the contact of outside air and surveyed sample, reduce the heat exchange of being surveyed sample and external, reduce the experiment and receive external factor's influence to it is more convenient to add the seed crystal through throwing the material branch pipe, need not take out survey pipe again, easy operation, efficiency is higher.
The refrigerating device can conveniently control the temperature required by the experiment, and does not need to control the temperature by adjusting the proportion of the added ice salt for many times in the experiment process. The electric control device is internally provided with an upper limit value and a lower limit value of an ice bath temperature sensor, the upper limit value is 2 ℃ lower than the theoretical freezing point of the solution, the lower limit value is 3 ℃ lower than the theoretical freezing point of the solution, when the temperature measured by the ice bath temperature sensor is lower than the lower limit value, the refrigeration equipment is turned off, and when the temperature is higher than the upper limit value of the temperature range, the refrigeration equipment is turned on, so that the frequent turning on and off of the refrigeration device can be avoided, and the phenomenon of serious supercooling or insufficient refrigeration can be avoided.
Magnetic stirrers is used for the horizontal mixing, and ice bath groove stirring rod and survey pipe stirring rod are used for manual stirring from top to bottom, and horizontal mixing and stirring matched with mode from top to bottom can not make the stirring rod collide survey inside pipe wall and thermometer, reduce the risk that measuring instrument damaged, through using magnetic stirrers, still be convenient for control stirring speed in the experimentation.
The invention adopts the method of first measuring and then accurately measuring to measure the freezing point, so that the operator does not need to keep high concentration of spirit all the time in the initial accurate measurement operation stage, the excessive stress of the operator can be avoided, and the energy is concentrated when the temperature is reduced to 0.7 ℃ higher than the initial measurement freezing point, so that the energy distribution of the operator is more reasonable.
Drawings
FIG. 1 is a schematic structural view of the present invention;
FIG. 2 is a schematic view of the ice bath apparatus of the present invention;
FIG. 3 is a top plan view of the ice bath cover of the present invention;
fig. 4 is a schematic view of the control panel of the present invention.
Detailed Description
As shown in fig. 1, 2, 3 and 4, the freezing point measuring device of the present invention comprises an ice bath device, a refrigerating device and a cold trap 22 for placing the ice bath device, wherein the ice bath device comprises an ice bath tank 1, a measuring tube 12, a measuring tube stirring rod 9 inserted into the measuring tube 12 and an ice bath tank stirring rod 6 inserted into the ice bath tank 1,
an ice bath upper cover 5 is arranged at the upper end of the ice bath 1, the ice bath upper cover 5 is connected with the ice bath 1 in a buckling mode, the ice bath upper cover 5 is provided with a large test tube hole 14 and a small test tube hole 15 matched with the measuring tube 12, an air sleeve 2 is inserted into the large test tube hole 14, an air sleeve plug 13 used for sealing the air sleeve 2 is arranged at the upper end of the air sleeve 2, the measuring tube 12 penetrates through the air sleeve plug 13 and is inserted into the air sleeve 2, and a gap is formed between the outer wall of the measuring tube 12 and the inner wall of the air sleeve 2; the upper end of the measuring pipe 12 is provided with a measuring pipe upper cover 11, the bottom ends of the ice bath stirring rod 6 and the measuring pipe stirring rod 9 are respectively provided with an annular stirring part, the measuring pipe 12 is outwards communicated with a feeding branch pipe 8 which is inclined upwards, the feeding branch pipe 8 is arranged between an air sleeve plug 13 and the measuring pipe upper cover 11, and the top end of the feeding branch pipe 8 is provided with a branch pipe plug 7 for sealing the feeding branch pipe 8;
the refrigeration device comprises a compressor 18, a condenser 19, a capillary tube 21 and a coil evaporator 23, wherein the compressor 18, the condenser 19, the capillary tube 21 and the coil evaporator 23 are sequentially connected through a refrigerant pipeline in a circulating manner, the condenser 19 is provided with radiating fins 20, and the coil evaporator 23 is wound around a cold trap 22;
a magnetic stirrer 24 is arranged at the lower side of the bottom of the cold trap 22, and magnetic stirrers 17 corresponding to the magnetic stirrer 24 are respectively arranged at the inner side of the bottom of the ice bath tank 1 and the bottom of the measuring tube 12.
The ice bath tank upper cover 5 and the ice bath tank 1 are buckled and connected by a specific structure: four edge buckles 4 capable of being turned are evenly fixed on the periphery of the ice bath tank upper cover 5, grooves 25 are formed in the edge buckles 4, and four protrusions 3 matched with the grooves 25 are arranged on the periphery of the upper end of the ice bath tank 1.
The digital Beckmann thermometer is connected with a temperature probe 26, the temperature probe 26 penetrates through the upper measuring pipe cover 11, is inserted into the measuring pipe 12 and is sleeved in the annular stirring part at the bottom end of the measuring pipe stirring rod 9 at intervals, the ice bath temperature sensor 27 penetrates through the upper ice bath groove cover 5, is inserted into the ice bath groove 1 and is sleeved in the annular stirring part at the bottom end of the ice bath groove stirring rod 6 at intervals, the digital Beckmann thermometer and the ice bath temperature sensor 27 are connected with the electric control device 28 through data lines, the electric control device 28 is further connected with the magnetic stirrer 24 and the compressor 18 respectively, and the electric control device 28 is connected with a power switch 31, a speed regulating knob 32 for regulating the stirring speed of the magnetic stirrer 24 and a display screen 30 for displaying the readings of the digital Beckmann thermometer and the ice bath temperature sensor 27.
The electric control device 28 refers to a PLC, a single chip microcomputer, or an integrated circuit.
A method for determining freezing point using a freezing point measuring device, comprising the steps of:
(1) Preparation of the assay
An operator adds crushed ice, tap water and salt into the ice bath tank 1, puts the magnetic stirrer 17 into the bottom of the ice bath tank 1, buckles the ice bath tank upper cover 5 with the ice bath tank 1, puts the ice bath tank 1 into the cold trap 22, puts the air sleeve 2 into the ice bath tank 1 through the large test tube hole 14, and opens the refrigeration equipment and the digital Beckmann thermometer;
an operator inserts an ice bath temperature sensor 27 into an ice bath tank 1, pulls an ice bath tank stirring rod 6 to stir up and down in the ice bath tank 1, an electric control device 28 is internally provided with an upper limit value and a lower limit value of the ice bath temperature sensor 27, the upper limit value is 2 ℃ lower than the theoretical freezing point of a solvent, the lower limit value is 3 ℃ lower than the theoretical freezing point of the solvent, when the temperature measured by the ice bath temperature sensor 27 is lower than the lower limit value, refrigeration equipment is closed, when the temperature is higher than the upper limit value of the temperature range, the refrigeration equipment is started, when the ice bath temperature is maintained to be 2-3 ℃ lower than the theoretical freezing point of distilled water, stirring is stopped, a 'keeping' key on a digital Beckman thermometer is pressed, a base temperature is locked, a measuring range is selected, 0 grade is generally selected, the digital Beckman thermometer is a conventional device in the field, the 'keeping' key is arranged on the digital Beckman thermometer, the measuring range can be selected, and the specific structure of the digital Beckman thermometer is not detailed any more;
an operator accurately transfers 25ml of distilled water into a clean and dry measuring tube 12 by using a pipette, puts a magnetic stirring bar 17 into the measuring tube 12, inserts a temperature probe 26 of a digital Beckmann thermometer into an upper cover 11 of the measuring tube, and then seals the upper cover 11 of the measuring tube to the measuring tube 12; the operator immerses the temperature probe 26 in the distilled water in the measuring tube 12, and locates at the center position of the measuring tube 12, so that the end of the temperature probe 26 is 5mm away from the bottom of the measuring tube 12 and does not collide with any substance;
(2) Crude determination of the freezing point of the solvent
An operator inserts the measuring tube 12 filled with the solvent into the ice bath 1 from the small test tube hole 15, adjusts the speed of the magnetic stirrer 24, adjusts the speed adjusting knob 32 to a proper position, observes the indication value of the digital Beckmann thermometer through the display screen 30 until the indication value is stable and unchanged, and the indication value of the digital Beckmann thermometer is the initial measuring solidification point of the pure solvent sample;
(3) Determination of the freezing point of a solvent
An operator takes out the measuring tube 12, dries the tube, holds the tube with palm for heating, after the ice in the measuring tube 12 to be measured is completely melted, inserts the measuring tube 12 into the ice bath 1 from the small test tube hole 15, when the temperature in the measuring tube 12 is reduced to 0.7 ℃ higher than the initial measuring freezing point, the measuring tube 12 is taken out rapidly, if the temperature is not taken out in time, the temperature is reduced to below 0.3 ℃ higher than the initial measuring freezing point rapidly, and the experiment failure is easy to cause. Taking out, wiping, inserting into the air sleeve 2, and recording the temperature value in the measuring tube 12 in time; the speed regulation knob is adjusted to slowly stir so as to lead the temperature to be uniformly reduced, and the indication value of the digital Beckmann thermometer displayed on the display screen 30 is recorded every 30 seconds; when the temperature is lower than the initial measurement freezing point, the speed regulation knob is adjusted in time to accelerate stirring and provide a condensation center to separate out solids, heat is released when the solids are separated out, when the temperature rises to be not less than 0.01 ℃, the speed regulation knob is adjusted to slowly stir, and the reason why the temperature is not less than the initial measurement freezing point is that in the actual operation, an operator probably cannot react to the temperature in time, so that the temperature exceeds 0.01 ℃, and the optimal operation of the operator is the subsequent operation of adjusting the speed regulation knob and the like when the temperature rises to be 0.01 ℃ (namely when the temperature starts to rise). When the temperature rises to the temperature which is not changed any more, the temperature lasts for 60 seconds, and the indication value of the digital Beckmann thermometer displayed by the display screen 30 is the freezing point of the distilled water; repeating the step (3) for 2 times, measuring the freezing point of the distilled water for three times, and taking the average value of the freezing points as the final measured freezing point of the distilled water;
(4) Determination of the freezing point of aqueous solutions of sucrose
An operator takes out the measuring tube 12, wipes the measuring tube dry, holds the measuring tube with palm to heat, after the freezing point of the measuring tube 12 is completely melted, 1-1.4 g of accurately weighed cane sugar is put in the measuring tube, after the cane sugar is completely dissolved, the freezing point of the primary measuring solution is measured, the measuring tube 12 filled with cane sugar aqueous solution is inserted into the ice bath 1 from the small test tube hole 15, the speed of the magnetic stirrer 24 is adjusted, the speed regulating knob 32 is adjusted to a proper position, the indication value of the digital Beckmann thermometer is observed through the display screen 30, the indication value of the display screen 30 is recorded every 30 seconds, the absolute value of the difference between every two recorded values is recorded as delta t, when the measuring tube 12 filled with cane sugar aqueous solution is inserted into the small test tube hole 15 of the ice bath 1, the difference between two adjacent delta t is less than 0.01 ℃ (when no solvent is solidified, the concentration of the cane sugar aqueous solution is kept unchanged at the initial stage, so that the cane sugar aqueous solution is in a state of uniform temperature reduction, when the solid solvent is precipitated, the temperature of the water is reduced by the primary measuring tube, and the reciprocal value of the primary measuring tube is recorded as the reciprocal value of the reciprocal of the primary measuring tube 30.01 when the last delta t is reached to be displayed; then precisely measuring the freezing point of the sucrose aqueous solution, (at the initial stage of precise measurement, the operator does not need to keep spirits highly concentrated all the time, and the excessive mental stress of the operator can be avoided), taking out the measuring tube 12, wiping, holding and heating with palm, inserting the measuring tube 12 into the ice bath 1 from the small test tube hole 15 after the icing in the measuring tube 12 is completely melted, quickly taking out the measuring tube 12 when the temperature is reduced to 0.7 ℃ higher than the initial measuring freezing point, wiping, inserting into the air sleeve 2, and recording the temperature value in the measuring tube at the moment in time; the speed regulation knob is adjusted to stir slowly to enable the temperature to drop uniformly, the indication value of the digital Beckmann thermometer displayed by the display screen 30 is recorded at intervals of 30 seconds, and the absolute value of the difference value between every two recorded values is recorded as delta T; when the temperature is lower than the initial measurement solidification point, adjusting a speed regulation knob in time to accelerate stirring and provide a condensation center to separate out solids, and when the temperature rises to be not less than 0.01 ℃, adjusting the speed regulation knob to slowly stir; when the last time delta T is lower than the last time delta T by more than 0.01 ℃, the indication value of the display screen 30 recorded for the penultimate time is used as the accurate measurement freezing point of the sucrose aqueous solution; repeating the step of precisely measuring the freezing point of the sucrose aqueous solution for 2 times, measuring the freezing points of the sucrose aqueous solution for three times, and taking the average value of the freezing points as the finally measured freezing point of the sucrose aqueous solution;
when the temperature of the solution is reduced to be below the freezing point of the initial testing solvent, if no ice is separated out from the sucrose aqueous solution, indicating that the supercooling phenomenon occurs, a seed crystal needs to be added into the testing tube 12, at the moment, the branch tube plug 7 is taken down, and the seed crystal is put into the testing tube 12 from the feeding branch tube 8;
(5) The refrigeration equipment and the digital beckmann thermometer were turned off.
During the measurement, there is one section air isolation between air jacket 2 and survey pipe 12, can play the effect that slows down heat transfer and uniform temperature, prevents the emergence of the excessive phenomenon of subcooling, if need not air jacket 2, survey pipe 12 disect insertion ice bath 1, survey the measured sample temperature in the pipe 12 and descend too fast, be difficult for producing new phase, produce strong subcooling phenomenon easily, the supercooled liquid can't form, finally leads to the experiment failure.
The refrigeration principle of the refrigeration device is as follows: after throttling and pressure reducing of the capillary tube 21, the refrigerant is quickly evaporated and absorbs heat in the coil evaporator 23, absorbs heat in the cold trap 22, enters the condenser 19 to be condensed under the action of the compressor 18, releases the heat to the outside, is condensed into liquid, throttles and reduces pressure of the refrigerant again through the capillary tube 21, and then circulates to refrigerate.
When the temperature drops to below the initial survey solvent freezing point, it does not have ice to separate out in the survey sample, need add the seed crystal in survey pipe 12, at this moment, take off branch pipe stopper 7, from throw material branch pipe 8 locate to survey in the pipe 12 in throw the seed crystal can, compare and take off survey pipe 12 upper cover, throw in the seed crystal from survey pipe 12 top, can reduce the contact of outside air and survey sample like this, reduce the heat exchange of survey sample and external world, the reduction experiment receives external factor's influence.
The ice bath tank upper cover 5 is connected with the ice bath tank 1 in a buckling mode, so that the ice bath tank upper cover 5 is buckled more conveniently and firmly, the cover can be prevented from rotating during stirring, the sealing performance of the ice bath tank 1 is improved, internal and external heat exchange is reduced, and the experiment temperature control is facilitated.
The ice bath stirring rod 6 and the measurement tube stirring rod 9 are used for manually stirring the ice bath in the ice bath 1 and the sample to be measured in the measurement tube 12 up and down, respectively. Magnetic stirrer 24 was used in combination with magnetic stirrer 17 to horizontally stir the ice bath in ice bath 1 and the sample to be measured in measuring tube 12.
The digital beckmann thermometer, the compressor 18, the condenser 19, the capillary tube 21, the coil evaporator 23 and the magnetic stirrer 24 are conventional devices, and detailed description thereof will not be given.
The present embodiment is not intended to limit the shape, material, structure, etc. of the present invention in any way, and any simple modification, equivalent change and modification made to the above embodiment according to the technical essence of the present invention are all within the scope of the technical solution of the present invention.
Claims (3)
1. Freezing point survey device, including ice bath device, refrigerating plant and be used for placing ice bath device's cold trap, ice bath device includes ice bath groove, survey pipe, inserts survey intraductal survey pipe stirring rod and inserts the ice bath groove stirring rod of ice bath groove, its characterized in that:
an ice bath upper cover is arranged at the upper end of the ice bath, the ice bath upper cover is buckled and connected with the ice bath, a large test tube hole and a small test tube hole matched with the measuring tube are formed in the ice bath upper cover, an air sleeve is inserted into the large test tube hole, an air sleeve plug used for sealing the air sleeve is arranged at the upper end of the air sleeve, the measuring tube penetrates through the air sleeve plug and is inserted into the air sleeve, and a gap is formed between the outer wall of the measuring tube and the inner wall of the air sleeve; the upper end of the measuring pipe is provided with an upper measuring pipe cover, the bottom ends of the ice bath tank stirring rod and the measuring pipe stirring rod are respectively provided with an annular stirring part, the measuring pipe is outwards communicated with a feeding branch pipe which is inclined upwards, the feeding branch pipe is arranged between the air sleeve plug and the upper measuring pipe cover, and the top end of the feeding branch pipe is provided with a branch pipe plug used for sealing the feeding branch pipe;
the refrigeration device comprises a compressor, a condenser, a capillary tube and a coiled evaporator, wherein the compressor, the condenser, the capillary tube and the coiled evaporator are circularly connected through a refrigerant pipeline in sequence, the condenser is provided with radiating fins, and the coiled evaporator is coiled around a cold trap;
a magnetic stirrer is arranged on the lower side of the bottom of the cold trap, and magnetic stirrers corresponding to the magnetic stirrer are respectively arranged on the inner side of the bottom of the ice bath and the bottom of the measuring tube;
the digital Beckmann thermometer is connected with a temperature probe, the temperature probe penetrates through the upper cover of the measuring tube to be inserted into the measuring tube and is sleeved in the annular stirring part at the bottom end of the stirring rod of the measuring tube at intervals, the ice bath temperature sensor penetrates through the upper cover of the ice bath to be inserted into the ice bath and is sleeved in the annular stirring part at the bottom end of the stirring rod of the ice bath at intervals, the digital Beckmann thermometer and the ice bath temperature sensor are connected with the electric control device through data lines, the electric control device is further connected with the magnetic stirrer and the compressor respectively, and the electric control device is connected with a power switch, a speed regulating button for regulating the stirring speed of the magnetic stirrer and a display screen for displaying the readings of the digital Beckmann thermometer and the ice bath temperature sensor.
2. The freezing point assay device of claim 1, wherein: the ice bath upper cover and the ice bath groove are buckled and connected by a specific structure that: four side buckles are uniformly fixed on the periphery of the upper cover of the ice bath tank, a groove is arranged on each side buckle, and four bulges matched with the grooves are arranged on the periphery of the upper end of the ice bath tank.
3. A method for measuring freezing point using the freezing point measuring device according to claim 1, characterized in that it comprises the steps of:
(1) Preparation of the assay
An operator adds crushed ice, tap water and salt into an ice bath tank, places a magnetic stirrer at the bottom of the ice bath tank, buckles an upper cover of the ice bath tank with the ice bath tank, places the ice bath tank into a cold trap, places an air sleeve into the ice bath tank through a large test tube hole, and opens a refrigeration device and a digital Beckmann thermometer;
an operator inserts an ice bath temperature sensor into an ice bath tank, pulls an ice bath tank stirring rod to stir up and down in the ice bath tank, an electric control device is internally provided with an upper limit value and a lower limit value of the ice bath temperature sensor, the upper limit value is 2 ℃ lower than the theoretical freezing point of a solvent, the lower limit value is 3 ℃ lower than the theoretical freezing point of the solvent, when the temperature measured by the ice bath temperature sensor is lower than the lower limit value, refrigeration equipment is closed, when the temperature is higher than the upper limit value of the temperature range, the refrigeration equipment is started, when the ice bath temperature is maintained to be 2-3 ℃ lower than the theoretical freezing point of distilled water, stirring is stopped, a 'keeping' key on a digital Beckman thermometer is pressed down, and the basic temperature is locked;
an operator accurately transfers 25ml of distilled water into a clean and dry measuring tube by using a pipette, a magnetic stirrer is placed into the measuring tube, a temperature probe of a digital Beckmann thermometer is inserted into an upper cover of the measuring tube, then the upper cover of the measuring tube is closed, the temperature probe is immersed into the distilled water in the measuring tube and is positioned at the central position inside the measuring tube, and the end part of the temperature probe is 5mm away from the bottom of the measuring tube and does not collide with any substance;
(2) Crude determination of the freezing point of the solvent
An operator inserts the measuring tube filled with the solvent into the ice bath from the small test tube hole, adjusts the speed regulating knob to a proper position, observes the indicating value of the digital Beckmann thermometer through the display screen until the indicating value is stable and unchanged, and the indicating value of the digital Beckmann thermometer is the initial measuring solidification point of the pure solvent sample;
(3) Determination of the freezing point of a solvent
An operator takes out the measuring tube, dries the measuring tube, holds the measuring tube with a palm for heating, inserts the measuring tube into the ice bath from the small test tube hole after the ice in the measuring tube is completely melted, quickly takes out the measuring tube when the temperature in the measuring tube is reduced to be 0.7 ℃ higher than the initial measuring freezing point, dries the measuring tube, inserts the measuring tube into the air sleeve, and records the temperature value in the measuring tube in time; the speed regulation knob is adjusted to slowly stir so as to lead the temperature to be uniformly reduced, and the indication value of the digital Beckmann thermometer displayed by the display screen is recorded at intervals of 30 seconds; when the temperature is lower than the initial measurement solidification point, adjusting a speed regulation knob in time to accelerate stirring and provide a condensation center to separate out solids, and when the temperature rises to be not less than 0.01 ℃, adjusting the speed regulation knob to slowly stir; when the temperature rises to the temperature which is not changed any more, the temperature lasts for 60 seconds, and the indication value of the digital Beckmann thermometer displayed by the display screen is the freezing point of the distilled water; repeating the step (3) for 2 times, measuring the freezing points of the distilled water for three times, and taking the average value of the freezing points as the final measured freezing point of the distilled water;
(4) Determination of the freezing point of aqueous solutions of sucrose
An operator takes out the measuring tube, wipes the measuring tube dry, holds the measuring tube with a palm for heating, after the measuring tube is frozen and completely melts, 1-1.4 g of accurately weighed cane sugar is put into the measuring tube, after the cane sugar is completely dissolved, the freezing point of the solution is initially measured, the measuring tube of the cane sugar aqueous solution is inserted into an ice bath from a small test tube hole, the speed of a magnetic stirrer is adjusted, a speed regulating knob is adjusted to a proper position, the indication value of the digital Beckmann thermometer is observed through a display screen, the indication value of the display screen is recorded every 30 seconds, the absolute value of the difference value between every two recorded values is recorded as delta t, the difference value of delta t of two adjacent times is less than 0.01 ℃ in the initial stage of inserting the measuring tube filled with the cane sugar aqueous solution into the small test tube hole of the ice bath, and when the delta t of the last time is lower than the value of the delta t of the last time by more than 0.01 ℃, the indication value of the display screen recorded in the last time is taken as the initial measurement of the freezing point of the cane sugar aqueous solution; then accurately measuring the freezing point of the sucrose aqueous solution, taking out the measuring tube, wiping the measuring tube dry, holding the measuring tube with a palm for heating, inserting the measuring tube into an ice bath from a small test tube hole after the ice in the measuring tube is completely melted, quickly taking out the measuring tube when the temperature is reduced to 0.7 ℃ higher than the initial measuring freezing point, wiping the measuring tube dry, inserting the measuring tube into an air sleeve, and recording the temperature value in the measuring tube at the moment in time; the speed regulation knob is adjusted to stir slowly to enable the temperature to drop uniformly, the indication value of the digital Beckmann thermometer displayed by the display screen is recorded at intervals of 30 seconds, and the absolute value of the difference value between every two recorded values is recorded as delta T; when the temperature is lower than the initial measurement solidification point, adjusting a speed regulation knob in time to accelerate stirring and provide a condensation center to separate out solids, and when the temperature rises to be not less than 0.01 ℃, adjusting the speed regulation knob to slowly stir; when the last time delta T is lower than the last time delta T by more than 0.01 ℃, the indication value of the display screen recorded for the penultimate time is used as the accurate measurement freezing point of the sucrose aqueous solution; repeating the step of precisely measuring the freezing point of the sucrose aqueous solution for 2 times, measuring the freezing points of the sucrose aqueous solution for three times, and taking the average value of the freezing points as the finally measured freezing point of the sucrose aqueous solution;
when the temperature of the solution is reduced to be below the freezing point of the initially-measured solvent, if no ice is separated out from the sucrose aqueous solution, taking down a branch pipe plug, and putting seed crystals into the measuring pipe from a feeding branch pipe;
(5) The refrigeration equipment and the digital beckmann thermometer were turned off.
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| CN108051274A (en) * | 2018-02-10 | 2018-05-18 | 济南盛泰电子科技有限公司 | A kind of alcoholic strength detects pretreating device |
| CN108562606B (en) * | 2018-03-20 | 2023-11-10 | 武汉研润科技发展有限公司 | Engine coolant freezing point tester |
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