Method and apparatus for measuring molar mass and molar enthalpy of vaporization of liquid organic substances

Abstract

The present application relates to a kind of methods and devices for measuring molar mass and molar evaporation enthalpy of liquid organic matter.The water vapor distillation device includes distillation adapter, and distillation adapter is composed of left straight pipe of distillation adapter and right straight pipe of distillation adapter in communication;The thermometer is connected above left straight pipe of distillation adapter, and flask is connected below;The spherical condenser pipe is connected above right straight pipe of distillation adapter, and scale receiving tube is connected below.The present application also provides a method for measuring molar mass and molar evaporation enthalpy of liquid organic matter using water vapor distillation device.The device can be assembled according to the requirements of scientific research and teaching, and can be reused.The cost of each component is low, and the components can be replaced individually, which is not easy to wear out, and effectively reduces the experimental cost.The method for measuring molar mass and molar evaporation enthalpy of liquid organic matter makes full use of water vapor distillation method, with the advantages of low distillation temperature, simple device, easy operation and no need for high-temperature heat source.

Description

Technical Field

[0001] This invention relates to a method and apparatus for measuring the molar mass and molar enthalpy of vaporization of liquid organic compounds. Specifically, it utilizes steam distillation to measure the molar mass and molar enthalpy of vaporization of unknown organic compounds, belonging to the field of physicochemical parameter testing technology for organic compounds. Background Technology

[0002] Measuring the molar enthalpy of vaporization of liquid organic compounds is a fundamental experiment in physical chemistry and chemical engineering thermodynamics. In basic physical chemistry lab courses, the static method, commonly known as the "determination of saturated vapor pressure of a liquid," is a frequently used method for measuring the molar enthalpy of vaporization of liquid organic compounds. The dynamic method, also known as the boiling point meter method, is also used in some scenarios. Both methods are based on the Clausius-Clapeyron equation and are mandatory experiments in the physical chemistry thermodynamics section.

[0003] In basic physical chemistry experimental teaching, the static method is almost always the preferred option in universities: this method can fully demonstrate the principles of thermodynamics, covering vacuum technology operation and data graphical methods, and is a classic project for training students' experimental skills. The dynamic method is a good alternative when experimental conditions are limited or when simplicity of operation is desired. Other methods, such as calorimetry and differential scanning calorimetry, are generally offered as extension content or instrumental analysis experiments.

[0004] The static method directly measures the saturated vapor pressure of a pure liquid at different temperatures and calculates the molar enthalpy of vaporization by plotting lnp against 1 / T. The principle is intuitive, and the data obtained is reliable. However, this method also has significant limitations in practical operation: its apparatus is complex, with numerous vacuum system connection points, making it prone to leaks; the degassing process requires repeated evacuation, boiling, and condensation operations, making the process cumbersome and time-consuming. If the degassing is incomplete, the measured "saturated vapor pressure" is actually the sum of the vapor pressure of the liquid being tested and the partial pressure of residual air, resulting in a significant positive deviation. Furthermore, the static method is not suitable for thermally unstable or high-boiling-point organic compounds.

[0005] The dynamic method calculates the enthalpy of vaporization by directly measuring the boiling point of a liquid under different external pressures. During the experiment, the liquid is in a continuous boiling state, and the vapor continuously carries away air, thus automatically eliminating the influence of dissolved gases, making the operation relatively simple and quick. However, the liquid is prone to superheating during boiling, leading to a measured temperature higher than the true vapor-liquid equilibrium temperature, resulting in a positive deviation. Furthermore, the experiment requires maintaining a constant system pressure using a needle valve and a buffer bottle, demanding a certain level of operational skill from the operator. Additionally, this method is not suitable for liquids that are prone to explosive boiling or foaming. Summary of the Invention

[0006] To address the shortcomings of existing technologies, this invention provides a method for measuring the molar mass and molar enthalpy of vaporization of liquid organic compounds.

[0007] The technical solution of this invention is as follows:

[0008] A steam distillation apparatus, comprising a distillation initiator;

[0009] The distillation connector consists of a connected left straight tube and a right straight tube.

[0010] A thermometer is connected to the upper part of the left straight tube of the distillation connector, and a flask is connected to the lower part.

[0011] A spherical condenser tube is connected above the right straight tube of the distillation connector, and a graduated receiving tube is connected below it.

[0012] According to a preferred embodiment of the present invention, the left straight pipe of the distillation connector and the right straight pipe of the distillation connector are connected by a branch pipe, and the branch pipe is inclined upward or downward in the horizontal direction by no more than 15 degrees.

[0013] According to a preferred embodiment of the present invention, a constant pressure branch is provided on the right side of the right straight tube of the distillation connector, and the constant pressure branch connects the right straight tube of the distillation connector and the scale receiving tube.

[0014] According to a preferred embodiment of the present invention, a piston is provided between the right straight tube of the distillation contactor and the scale receiving tube.

[0015] A method for measuring the molar mass and molar enthalpy of vaporization of a liquid organic compound using a steam distillation apparatus includes the following steps:

[0016] (1) Add the liquid organic compound to be tested and water to a flask to obtain a mixed liquid; then open the spherical condenser, stir and heat the mixed liquid to boiling, and record the boiling point t of the mixed liquid; then determine the saturated vapor pressure p of water at the boiling point t. 水 ; calculations show that at standard atmospheric pressure p θ At temperature t, the saturated vapor pressure p of the liquid organic compound to be tested B ;

[0017] (2) When the total amount of liquid distillate in the graduated receiving tube exceeds half, close the piston, let the liquid distillate cool to room temperature, and weigh it to obtain the mass m of water. 水 The mass m of the liquid organic matter to be tested B Then, based on the mass m of the liquid organic matter to be tested... B , saturated vapor pressure p of the liquid organic compound to be tested B saturated vapor pressure p of water 水 The mass of water m 水 Molar mass M of water 水 Calculations were performed to obtain the molar mass M of the liquid organic compound to be tested. B ;

[0018] (3) Based on the measurement of the saturated vapor pressure p of liquid organic matterB The boiling point t of the mixed liquid and the standard atmospheric pressure p θ The molar enthalpy of vaporization of the liquid organic compound under test was obtained by calculation using the Clausius-Clapeyron equation and the Trudeau rule.

[0019] According to a preferred embodiment of the present invention, in step (1), the volume ratio of the liquid organic matter to be tested to water is 1:(1~1.1).

[0020] More preferably, the volume ratio of the liquid organic matter to be tested to water is 1:1.

[0021] According to a preferred embodiment of the present invention, in step (1), the liquid organic matter to be tested includes liquid organic matter that is immiscible with water, such as carbon tetrachloride, cyclohexane, chloroethane, chloroform, chlorobenzene, bromobenzene, benzene, toluene, ethyl benzoate, limonene, terpinene, aromatic and aliphatic compounds, as well as natural essential oil compounds.

[0022] According to a preferred embodiment of the present invention, in step (1), the standard atmospheric pressure p θ The saturated vapor pressure p of the liquid organic compound to be tested is 100 kPa. B The calculation formula is: p B = p θ - p 水 .

[0023] According to a preferred embodiment of the present invention, in step (2), the molar mass M of the liquid organic compound to be tested is... B The formula for calculation is: .

[0024] According to a preferred embodiment of the present invention, in step (2), the Clausius-Clapeyron equation and the Trudeau rule are as follows:

[0025] , ;

[0026] Among them, △ vap H m For enthalpy of vaporization, T b R is the normal boiling point of the liquid under standard atmospheric pressure, and R is a constant of 8.314.

[0027] Experimental procedures not described in detail in this invention can be performed according to conventional experimental procedures in this technical field.

[0028] Beneficial effects:

[0029] 1. This invention provides a steam distillation apparatus that can be assembled according to scientific research and teaching requirements, is reusable, has low-cost components, can be replaced individually, is not easily damaged, and effectively reduces experimental costs.

[0030] 2. The method for measuring the molar mass and molar enthalpy of vaporization of liquid organic compounds provided by this invention utilizes the relationship between the mass ratio of the two liquids in the steam distillation product and the saturated vapor pressure and molar mass of the organic compound and water. Combined with the Clausius-Clapeyron equation and Truden's rule, the molar mass and molar enthalpy of vaporization of the unknown organic compound can be calculated. Compared with existing methods, this invention does not require complex instruments and equipment, can be easily performed by a single person, and provides accurate measurement data with minimal error.

[0031] 3. The method for measuring the molar mass and molar enthalpy of vaporization of liquid organic compounds provided by this invention fully utilizes steam distillation, which has the advantages of low distillation temperature, simple equipment, convenient operation, and no need for a high-temperature heat source. During the distillation process, heat-sensitive substances can be effectively protected from damage. It can effectively determine the molar mass and molar enthalpy of vaporization of organic compounds with high boiling points, poor thermal stability, and poor water solubility. Attached Figure Description

[0032] Figure 1 This is a schematic diagram of a steam distillation apparatus;

[0033] In the diagram: 1. Flask, 2. Left straight tube of distillation connector, 3. Thermometer, 4. Right straight tube of distillation connector, 5. Constant pressure branch, 6. Piston, 7. Spherical condenser, 8. Graduated receiving tube. Detailed Implementation

[0034] The present invention will now be described in detail with reference to specific embodiments. These embodiments are intended to help those skilled in the art to further understand the present invention, but do not limit the invention in any way. It should be noted that those skilled in the art can make various adjustments and improvements without departing from the concept of the present invention, and these all fall within the scope of protection of the present invention.

[0035] Example 1

[0036] like Figure 1 As shown, a steam distillation apparatus includes a distillation connector;

[0037] The distillation connector is composed of a left straight tube 2 and a right straight tube 4 of the distillation connector that are connected to each other;

[0038] A thermometer 3 is connected above the left straight tube 2 of the distillation connector, and a flask 1 is connected below it;

[0039] A spherical condenser tube 7 is connected above the right straight tube 4 of the distillation connector, and a graduated receiving tube 8 is connected below it.

[0040] The left straight pipe 2 of the distillation connector and the right straight pipe 4 of the distillation connector are connected by a branch pipe, which is inclined upward or downward in the horizontal direction by no more than 15 degrees.

[0041] A constant pressure branch pipe 5 is provided on the right side of the right straight pipe 4 of the distillation connector, and the constant pressure branch pipe 5 connects the right straight pipe 4 of the distillation connector and the scale receiving pipe 8.

[0042] A piston 6 is provided between the right straight tube 4 of the distillation contact and the scale receiving tube 8.

[0043] Example 2

[0044] A method for measuring the molar mass and molar enthalpy of vaporization of a liquid organic compound using the steam distillation apparatus described in Example 1 includes the following steps:

[0045] (1) Add 50 mL of carbon tetrachloride and 50 mL of water to flask 1 to obtain a mixed liquid; then open the spherical condenser 7, stir and heat the mixed liquid to boiling, and record the boiling point (t) of the mixed liquid as 66.5℃;

[0046] According to Antony's equation for water: Substituting t=66.5 into the calculation yields lgp 水 (mmHg) = 2.3011, the saturated vapor pressure (p) of water at this boiling point 水 )≈200.0 mmHg=200.0×0.133322≈26.6 kPa;

[0047] Next, the calculation formula is used: p B = p θ - p 水 , will p 水 =26.6 kPa, p θ Substituting 100 kPa into the calculation, we obtain the saturated vapor pressure (p) of carbon tetrachloride at this boiling point. B The Pa is 73.4 kPa.

[0048] (2) When the total amount of liquid distillate in the graduated receiving tube 8 exceeds half, close the piston 6, and weigh the liquid distillate after it cools to room temperature to obtain the mass (m) of water. 水 The mass of carbon tetrachloride is 0.60g, and the mass of carbon tetrachloride (m) is... B The content is 14.2g;

[0049] Based on the mass of carbon tetrachloride (m B ), saturated vapor pressure of carbon tetrachloride (p B ), the mass of water (m) 水 ), saturated vapor pressure of water (p) 水 ) and the molar mass of water (M) 水 Calculations were performed, and the molar mass of carbon tetrachloride was found to be 154.4 g / mol.

[0050] The specific calculation formula is as follows: ;

[0051] (3) Based on the saturated vapor pressure (p) of carbon tetrachloride B The boiling point (t) of the liquid mixture and its relationship with standard atmospheric pressure (p) θ The molar enthalpy of vaporization of carbon tetrachloride was calculated to be 30.7 kJ / mol using the Clausius-Clapeyron equation and the Truden rule.

[0052] The Clausius-Clapeyron equations and the Trudeau rule are as follows:

[0053] , ;

[0054] Among them, △ vap H m For enthalpy of vaporization, T b R is the normal boiling point of the liquid under standard atmospheric pressure, and R is a constant of 8.314.

[0055] Results Comparison: The standard molar mass of carbon tetrachloride is 153.8 g / mol, and the error between the result obtained by the method of this invention and that standard is 0.39%.

[0056] The standard molar enthalpy of vaporization of carbon tetrachloride at its normal boiling point is 30.0 kJ / mol, and the result obtained by the method of this invention has an error of 2.3%.

[0057] Example 3

[0058] A method for measuring the molar mass and molar enthalpy of vaporization of a liquid organic compound using the steam distillation apparatus described in Example 1 includes the following steps:

[0059] (1) Add 50 mL of cyclohexane and 50 mL of water to flask 1 to obtain a mixed liquid; then open the spherical condenser 7, stir and heat the mixed liquid to boiling, and record the boiling point of the mixed liquid as 68℃.

[0060] According to Antony's equation for water: Substituting t=68 into the calculation yields lgp 水 (mmHg) = 2.3298, the saturated vapor pressure (p) of water at this boiling point 水 )≈213.8 mmHg=213.8×0.133322≈28.5 kPa;

[0061] Next, the calculation formula is used: p B = p θ - p 水 , will p 水 =28.5kPa, p θSubstituting 100 kPa into the calculation, we obtain the saturated vapor pressure (p) of cyclohexane at this boiling point. B The Pa is 71.5 kPa.

[0062] (2) When the total amount of liquid distillate in the graduated receiving tube 8 exceeds half, close the piston 6, and weigh the liquid distillate after it cools to room temperature to obtain the mass (m) of water. 水 The mass of cyclohexane is 0.50g, and the mass of cyclohexane (m) is... B The weight is 6.10g;

[0063] Based on the saturated vapor pressure (p) of cyclohexane B ), the mass of cyclohexane (m) B ), the mass of water (m) 水 ), saturated vapor pressure of water (p) 水 ) and the molar mass of water (M) 水 Calculations show that the molar mass of cyclohexane is 87.5 g / mol.

[0064] The specific calculation formula is as follows: ;

[0065] (3) Based on the saturated vapor pressure (p) of cyclohexane B The boiling point (t) of the liquid mixture and its relationship with standard atmospheric pressure (p) θ The molar enthalpy of vaporization of cyclohexane was calculated to be 31.0 kJ / mol using the Clausius-Clapeyron equation and the Truden rule.

[0066] The Clausius-Clapeyron equations and the Trudeau rule are as follows:

[0067] , ;

[0068] Among them, △ vap H m For enthalpy of vaporization, T b R is the normal boiling point of the liquid under standard atmospheric pressure, and R is a constant of 8.314.

[0069] Results comparison: The standard molar mass of cyclohexane is 84.2 g / mol, and the error between the result obtained by the method of this invention and that standard is 3.9%.

[0070] The standard molar enthalpy of vaporization of cyclohexane at its normal boiling point is 30 kJ / mol, and the result obtained by the method of this invention has an error of 3.3%.

[0071] The above description is only a preferred embodiment of this patent. It should be noted that for those skilled in the art, several improvements and substitutions can be made without departing from the technical principles of this patent, and these improvements and substitutions should also be considered within the scope of protection of this patent.

Claims

1. A steam distillation apparatus, characterized in that, Including distillation leads; The distillation connector consists of a connected left straight tube and a right straight tube. A thermometer is connected to the upper part of the left straight tube of the distillation connector, and a flask is connected to the lower part. A spherical condenser tube is connected above the right straight tube of the distillation connector, and a graduated receiving tube is connected below it.

2. The steam distillation apparatus as described in claim 1, characterized in that, The left straight tube of the distillation connector and the right straight tube of the distillation connector are connected by a branch tube, which is inclined upward or downward at a degree not greater than 15 degrees in the horizontal direction; a constant pressure branch tube is provided on the right side of the right straight tube of the distillation connector, which is connected to the right straight tube of the distillation connector and the scale receiving tube.

3. The steam distillation apparatus as described in claim 1, characterized in that, A piston is provided between the right straight tube of the distillation connector and the scale receiving tube.

4. A method for measuring the molar mass and molar enthalpy of vaporization of a liquid organic compound using the steam distillation apparatus of claim 1, characterized in that, The steps include the following: (1) Add the liquid organic compound to be tested and water to a flask to obtain a mixed liquid; then open the spherical condenser, stir and heat the mixed liquid to boiling, and record the boiling point t of the mixed liquid; then determine the saturated vapor pressure p of water at the boiling point t. 水 ; calculations show that at standard atmospheric pressure p θ At temperature t, the saturated vapor pressure p of the liquid organic compound to be tested B ; (2) When the total amount of liquid distillate in the graduated receiving tube exceeds half, close the piston, let the liquid distillate cool to room temperature, and weigh it to obtain the mass m of water. 水 The mass m of the liquid organic matter to be tested B Then, based on the mass m of the liquid organic matter to be tested... B , saturated vapor pressure p of the liquid organic compound to be tested B saturated vapor pressure p of water 水 The mass of water m 水 Molar mass M of water 水 Calculations were performed to obtain the molar mass M of the liquid organic compound to be tested. B ; (3) Based on the measurement of the saturated vapor pressure p of liquid organic matter B The boiling point t of the mixed liquid and the standard atmospheric pressure p θ The molar enthalpy of vaporization of the liquid organic compound under test was obtained by calculation using the Clausius-Clapeyron equation and the Trudeau rule.

5. The method as described in claim 4, characterized in that, In step (1), the volume ratio of the liquid organic matter to be tested to water is 1: (1~1.1).

6. The method as described in claim 5, characterized in that, The volume ratio of the liquid organic matter to water is 1:

1.

7. The method as described in claim 4, characterized in that, In step (1), the liquid organic matter to be tested includes carbon tetrachloride, cyclohexane, chloroethane, chloroform, chlorobenzene, bromobenzene, benzene, toluene, ethyl benzoate, limonene, and terpinene.

8. The method as described in claim 4, characterized in that, In step (1), the standard atmospheric pressure p θ The saturated vapor pressure p of the liquid organic compound to be tested is 100 kPa. B The calculation formula is: p B = p θ - p 水 .

9. The method as described in claim 4, characterized in that, In step (2), the molar mass M of the liquid organic compound to be tested B The formula for calculation is: .

10. The method as described in claim 4, characterized in that, In step (2), the Clausius-Clapeyron equation and the Trudeau rule are as follows: ， ； Among them, △ vap H m For enthalpy of vaporization, T b R is the normal boiling point of the liquid under standard atmospheric pressure, and R is a constant of 8.314.

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