Isoteniscope-The Determination of the Saturated Vapor Pressure of Liquid-Experiments in Physical Chemistry

Purposes

1. Use the Clausius-Clapeyron equation to figure out the average molar enthalpy of vaporization of a liquid inside the measured temperatures.
2. To master measuring saturated vapor pressure of liquid.

Principle

    Vapor pressure is the pressure exerted by a vapor in thermodynamic equilibrium with its condensed phases (solid or liquid) at a given temperature in a closed system. The equilibrium vapor pressure is an indication of a liquid's evaporation rate. It relates to the tendency of particles to escape from the liquid.

The vapor pressure of any substance increases non-linearly with temperature according to the Clausius–Clapeyron relation:

Where R is gas constant, T is the temperature, p Is the pressure, Δvap Hm is the enthalpy of vaporization. 
When the change of the temperature is small, we can assume the enthalpy of vaporization is independent of temperature, this equation can be integrated as follows:

then 

or

where A is Δvap Hm/R , B is a integral constant.

According to the equation, we can get a line if we make (ln p)-(1/T) figure, and the slope “m” should be –A = -Δvap Hm/R. And then we get: 

And the boiling point can be figured out by the figure. 

Apparatus

1. An isoteniscope

2. A vacuum pump

Vacuum pump (right) and desiccators (middle) 

3. A barometer

Chemicals

1. Absolute Ethanol (A.R.)

Procedure

1. Stet up the apparatus as below:

2. Leak detection:
Turn off the H valve, and open the I, F, G valves. Turn on the vacuum pump until the pressure reaches 25~30 kPa and then turn off the I, F, G valves, and then turn off the pump. Wait for a minutes and check the value of the barometer. 

3. Heating:
Open the stirrer and adjust the voltage of the heater to about 160V.

An autotransformer

4. Degas:
When the temperature of the hot water bath is over 50℃, the ethanol inside the isoteniscope starts bubbling. Keep the temperature at about 52℃ for 5 minutes by adjusting the voltage of the heater.

5. The measurement of vapor pressure:
Open the H valve slowly let air defuse through the capillary, until the BC phase is matched and is stable at least 1 minute. Record the temperature of the hot water bath and the pressure of the barometer. Keep heating the water bath and do the same things 6~10 times after raise about 2 degrees every times.

6. Finish:
Turn on all the valves, turn off all the electronics, and clean up the table.

Report Sheet

Data Processing

Fitting with an exponential function, y = a*b^x , on the P-T figure.

Figure 1

Linear fitting on the ln(Pa)-1/T figure

Figure 2

From this fitting curve, we can get the enthalpy of vaporization by using the equation as follow: 

Δvap Hm = - (8.3144621 J / (K mol) ) x (-5172.43 K)
       = 43.0 kJ/mol 
We can also get the normal boiling point from the fitting curve.
y = 26.29912 - 5172.43*x
ln(101325 Pa) = 26.29912 – 5172.43x 
 x = 1/T
=>  T = 1/(((ln 101325) – 26.29912) /(.5172.43))
      = 350.12 K = 76.97 ℃

To compare with the literature datas

Reference

[1]  傅献彩, 沈文霞, 姚天扬. 物理化学, 上册欧4 版. 北京:高等教育出版社, 1990:144.

[2]  清华大学化学系物理化学实验编写组. 物理化学实验. 北京：清华大学出版社, 1991.

[3]  Robert C. Wcast Handbook of Chemistry and Physics. Physics. 58^th ed. Ohio: CRC Press, 1977.

[4]  朱文涛. 物理化学. 北京：清华大学出版社，1995.

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Contents

Organic Chemistry

1.     Use a Melting PointApparatus to Figure Out Eutectic Point

 

2.     Crystallization

 

3.     Extraction

 

4.     Sublimation - Extraction Caffeine from Tea Leaves

 

5.     Hydration Reaction of Alkenes 

 

6.     Preparation of Cyclohexene- Dehydration of Alcohols

 

7.     Hydroxylation - Oxidation of Alkenes

 

8.     Synthesis of n-Butyl Methyl Ether - SN2 Reactions

 

9.     Make Pure Nitrocellulose –Nitration

 

10. Preparation of Benzoin -Synthesis of Dilantin

 

11. Preparation of Benzil -Synthesis of Dilantin

 

12. Preparation of 5,5-diphenylhygantion - Synthesis of Dilantin

 

13. The Multistep Synthesis of Dilantin (5,5-diphenlyhydantion) from Benzaldehyde

 

14. The Diels-Alder Reaction of Anthracene with Maleic Anhydride

 

15. Synthesis of 1-Bromobutanefrom 1-Butanol - Chemistry of Alcohol

 

16. Synthesis of t-ButylChloride from t-Butyl Alcohol - Chemistry of Alcohol

 

17. Synthesis of 2-Methyl-2-Hexanol-The Grignard Reaction

 

18. Saponification and Hydrolysis-Carboxylic acid 

 

19. Fischer Esterification 

 

20. Sodium Borohydride Reduction of Acetophenone

 

21. Synthesis of p-nitroacetanilide-Nitration

 

22. Sunscreen-Preparation of Dibenzalacetone-Aldol Condensation

 

23. Preparation of Ethyl Acetoacetate- Claisen Condensation

 

24. Preparation of Acetamide - Amidation of Ester

 

25. Preparation of Thioacetamide - Organosulfur Compounds

 

26. Synthesis of Chloroform from Acetone and Bleach - Haloform Reaction

Analytical Chemistry

1.     The Systematic Analysis of Cation Group I

 

2.     The Systematic Analysis of Cation Group 2 - The Hydrogen Sulfide Group - Hg++, Cd++, Cu++, Pb++, Sn++,Sn(IV), Bi+++, Sb(III), Sb(V), As(III), As(V)

 

3.     The Systematic Analysis of Cation Group 3 - The Basic Hydrogen Sulfide Group - Al+++, Cr+++, Fe+++, Fe++,Mn++, Co++, Ni++, Zn++

 

4.     The Systematic Analysis of Cation Group 4 - The Ammonium Carbonate Group - Ca++, Sr++, Ba++ 

5.     The Systematic Analysis of Cation Group 5 - The Soluble Group - Na+, K+, Mg++, NH4+

 

6.     The Determination of Magnesium by Direct Titration

 

7.     The Determination of Calcium by Displacement Titration 

 

8.     Preparation and Standardization of 0.1M Sodium Thiosulfate

 

9.     The Determination of Copper in Brass 

 

10. The Determination of Ascorbic Acid in Vitamin C Talbets by Titration with Potassium Bromate

  

Inorganic Chemistry

1.     Silver chloride decompose 

 

2.     How to revive CaCl2 desiccant at home?

 

3.     From Calcium Metal to Enthalpy 

 

4.     Homemade Charcoal Pencils by Dry Distillation 

 

5.     A Light Bulb Without Electricity-Catalytic Oxidation of Ammonia on a Copper Wire

 

6.     Preparation of Anhydrous Nitric Acid 

 

7.     Preparation of Phosphorus Pentasulfide - A Thionation Reagent

 

Physics

1.     How to make the simplest magnetometer ? 

 

Biochemistry

1.     MTT assay 

 

2.     Ames test - Salmonella Reversion Assay 

 

3.     Cellular total RNA extraction from a ALL(Acute lymphocytic leukemia) patient's cells

4.     Making Red Yeast Rice (Monascus purpureus) 

 

Others

1.     Quinine, Quinidine and Tonic Water 

 

2.     Synthesis of Rayon 

 

3.     Making 99.5% Absolute Alcohol

 

4.     Luminol Reaction 

The Determination of Ascorbic Acid in Vitamin C Talbets by Titration with Potassium Bromate - Lu Le Laboratory

Standardization of Sodium Thiosulfate against Potassium Bromate

Discussion

Iodine is generated by the reaction between a known volume of standard potassium bromate and an unmeasured excess of potassium iodide:

BrO₃^- + 6 I^- + 6 H⁺ → Br^- + 3 I₂ + 3 H₂O

The iodine produced is titrated with the sodium thiosulfate solution.

Procedure

1.     Pipet 25.00-mL aliquots of the KBrO₃ solution into 250-mL a conical flask and rinse the interior walls with distilled water.

2.     Treat each sample individually beyond this point. Introduce 2 to 3 g of KI and about 5-mL of 3 M H₂SO₄. 

3.     Immediately titrate with Na₂S₂O₃ until the solution is pale yellow.

 

4.     Add 5-mL of starch indicator, and titrate with Na₂S₂O₃ to the disappearance of the blue color.

 

5.     Calculate the concentration of the thiosulfate solution.

The Determination of Ascorbic Acid in Vitamin C Tablets by Titration with Potassium Bromate

Discussion

Ascorbic Acid, is cleanly oxidized to dehydroascorbic acid by bromine:

An unmeasured excess of potassium bromide is added to an acidified solution of the sample. The solution is titrated with standard potassium bromate to the first permanent appearance of excess bromine; this excess is then determined iodometrically with standard sodium thiosulfate. The entire titration must be performed without delay to prevent air oxidation of the ascorbic acid.

Procedure

1.     Weight (to nearest milligram) 3 to 5 vitamin C tablets [1]. Pulveize them thoroughly in a mortar, and transfer the powder to a dry weighting bottle.

2.     Weight individual 0.40-g to 0.50-g samples (to the nearest 0.1mg) into dry 250-mL conical flasks.

3.     Treat each sample individually beyond this point. Dissolve the sample [2] in 50-mL of 1.5 M H₂SO₄; then add 5g of KBr.

 

4.     Titrate immediately with standard KBrO₃ to the first faint yellow due to excess Br₂. Record the volume of KBrO₃ used.

 

5.      Add 3 g of KI and 5-mL of starch indicator; back-titrate [3] with standard 0.05 M Na₂S₂O₃.

 

 

6.     Calculate the percentage of ascorbic acid in the sample.

Notes

[1] This method is not applicable to chewable vitamin C tablet.

[2] The binder in may vitamin C tablets remains in suspension throughout the analysis. If the binder is starch, the characteristic color of the complex with iodine appears on addition of KI.

[3] The volume of the thiosulfate needed for the back-titration seldom exceeds a few milliters.

Report Sheet

Concentration of Standard KBrO3 (aq)	0.0150 M
Concentration of Standard Na2S2O3 (aq)	0.0500 M
Weight of Vitamin C Samples
Sample 1	0.4000 g
Sample 2	0.4000 g
Titration
Test 1
Volume of KBrO3 (aq)	51.25 mL
Volume of Na2S2O3 (aq)	3.50 mL
Test 2
Volume of KBrO3 (aq)	51.20 mL
Volume of Na2S2O3 (aq)	3.10 mL
Weight of Vitamin C	(3x0.0150 x V(KBrO3) – (0.0500 x V(Na2S2O3) /2 ) x 176.12 x 10-3
Test 1	0.3910 g
Test 2	0.3920 g
Average Weight of Vitamin C	0.3920 g
Percentage Error	2.00 %
Assay of Vitamin C Sample	98.00%