Determination of the Aqua Surface Tension by Determining the Biggest Vacuole Pressure 退出

Content Purposes and Demands Purposes and Demands Purposes and Demands Purposes and Demands Principle PrinciplePrinciple Apparatus and Reagent Apparatus and Reagent Apparatus and Reagent Apparatus and Reagent procedure procedure procedure Data Records and Processing Data Records and Processing Data Records and Processing Data Records and Processing Questions Questions Questions Attentions Attentions Attentions Attentions Demonstrated Demonstrated Demonstrated

1.Determine surface tension of ethanol liquor in the terms of concentration. Figure out surface absorption capacity of ethanol and area of cross-section of ethanol molecule. 1.Determine surface tension of ethanol liquor in the terms of concentration. Figure out surface absorption capacity of ethanol and area of cross-section of ethanol molecule. Purposes and Demands

2.Understand surface tension, surface free energy and the relationship between surface and absorption. 2.Understand surface tension, surface free energy and the relationship between surface and absorption. 3.Command the technique and principle of the method using to determine the surface tension. 3.Command the technique and principle of the method using to determine the surface tension.

Principle 1. Surface free energy 1. Surface free energy Surface tension shows whether liquid surface tends to shrink automatically. The value depends on concentration and component of liquid, temperature and atmosphere. Surface tension shows whether liquid surface tends to shrink automatically. The value depends on concentration and component of liquid, temperature and atmosphere.

2. Surface absorption 2. Surface absorption The lowest energy principle says, if surface tension of solvent can be reduce by a solute, the concentration of surface solute is bigger than interior, contrarily, if a solute make surface tension of solvent increase, the concentration of surface solute is lower than interior. The lowest energy principle says, if surface tension of solvent can be reduce by a solute, the concentration of surface solute is bigger than interior, contrarily, if a solute make surface tension of solvent increase, the concentration of surface solute is lower than interior.

The phenomenon that concentration of solute in exterior and interior are not identical is called surface absorption. Among them, there are a well-known equation Gibbs isotherm we find:

where Γ is the surface absorption quantity; T, C, and R are, respectively,thermodynamics temperature, concentration, and gas constant.

Measurements have shown that in dilute solution the surface tension increases linearly with concentration. Draw a graph of surface tension toward concentration. Make tangent to an arbitrarily point on the curve and the corresponding slope σ/dci. Then figure out all the valves of and draw the graph of Γ against c. Measurements have shown that in dilute solution the surface tension increases linearly with concentration. Draw a graph of surface tension toward concentration. Make tangent to an arbitrarily point on the curve and the corresponding slope σ/dci. Then figure out all the valves of and draw the graph of Γ against c.

3. The biggest vacuole pressure 3. The biggest vacuole pressure Fill liquid in a measuring tube until the liquid level outside is at or slightly above the zero point of the capillary tube. The liquid level inside the capillary tube would rise. Start the pump and there is a pressure degression in the measuring tube. Fill liquid in a measuring tube until the liquid level outside is at or slightly above the zero point of the capillary tube. The liquid level inside the capillary tube would rise. Start the pump and there is a pressure degression in the measuring tube.

For the pressure dispatch among the measuring tube and capillary, liquid level in the capillary tube would be pressed down to nozzle and air bubble is shaped. Curvature radius of the air bubble increases until it is equal to radius of capillary tube. According to the Laplace formulae, the maximal pressure dispatch the air bubble endure can be expressed:

also, it can be expressed by the high dispatch in the U manometer ：  p ma x=ghx=gh K ’, apparatus constant, can be determined base on known surface tension. (Surface tension of water and ethanol liquor can be looked up on appendix)

Apparatus and Reagent Measuring detector of surface tension 1 Measuring detector of surface tension 1 Abbe refractometer 1 Abbe refractometer 1 Beaker(200ml) 1 Beaker(200ml) 1 Thermostatic water bath 1 Thermostatic water bath 1 Spheric aspirator Spheric aspirator Enthanol(analytically pure) 1 Enthanol(analytically pure) 1

Procedure 1. Determination of instrumental constant 1. Determination of instrumental constant Regulate the thermostatic bath at the temperature of 30±0.1 o C. Regulate the thermostatic bath at the temperature of 30±0.1 o C. If the instruments have been recently cleaned, immerse ethanol liquor to measuring tube until the liquor level outside is at or slightly above the zero point of the capillary tube, then mounted the instrument in the thermostatic bath for 10 min. If the instruments have been recently cleaned, immerse ethanol liquor to measuring tube until the liquor level outside is at or slightly above the zero point of the capillary tube, then mounted the instrument in the thermostatic bath for 10 min.

Be sure to keep the capillary tube vertical. Assemble the instruments following the Sketch- maps of Equipments. Turn on the pump for beginning. Note that the bubbles shape at a steady speed, usually likely for 8-12 per min. Mark down three times both the highest and lowest reading of liquid level in two arms of U manometer. Figure out the average number and Δh. Be sure to keep the capillary tube vertical. Assemble the instruments following the Sketch- maps of Equipments. Turn on the pump for beginning. Note that the bubbles shape at a steady speed, usually likely for 8-12 per min. Mark down three times both the highest and lowest reading of liquid level in two arms of U manometer. Figure out the average number and Δh.

2.Determination of surface tension of ethanol solution 2.Determination of surface tension of ethanol solution Repeat the same procedure, measure Δh in terms of concentration ethanol solution which begins with high concentration solution to low one. Before each determination measuring tube and capillary tube must be washed three times with liquid that will be determined. Repeat the same procedure, measure Δh in terms of concentration ethanol solution which begins with high concentration solution to low one. Before each determination measuring tube and capillary tube must be washed three times with liquid that will be determined.

Sketch-maps of Equipments

Data Records and Processing 1. Room temperature: 1. Room temperature: Atmosphere pressure: Atmosphere pressure: σ H2O = σ H2O =  h H2O =  h H2O = Instrumental constant: Instrumental constant:

2. Fill the table with experiment data: C enthanol Δh=h 上 -h 下 /cm σ /N · m -1 Γ /mol · m -2 C（M）C（M） 123 averag e

3. Draw the graph of surface tension σ toward concentration. 3. Draw the graph of surface tension σ toward concentration. 4. Draw the graph of dσ/dci against concentration. 4. Draw the graph of dσ/dci against concentration. 5. Draw the graph of Γ against concentration. 5. Draw the graph of Γ against concentration.

Questions 1. What’s the meaning of surface tension and surface free energy? What’ the relationship between surface tension and temperature? 1. What’s the meaning of surface tension and surface free energy? What’ the relationship between surface tension and temperature? 2. How to understand about positiveabsorption and negative absorption? 2. How to understand about positiveabsorption and negative absorption? What variable did the experiment using Cibbs isotherm to determine, and what data else need to know? What variable did the experiment using Cibbs isotherm to determine, and what data else need to know?

4 Why should we determine instrumental constant? 4 Why should we determine instrumental constant? 5. What’s the result if fill the manometer ethanol liquor instead of water? 5. What’s the result if fill the manometer ethanol liquor instead of water? 6. What’s the most important factor effect the experiment? 6. What’s the most important factor effect the experiment?

Attentions Make sure that the liquor level outside is tangency with capillary. Make sure that the liquor level outside is tangency with capillary. Air bubble form steadily. Air bubble form steadily.

Abbe refractometer The figure shows the best state of visual field that has is a sharp boundary between light and dark fields The reading is n ＝

Surfactant molecule can lie low on surface of solution when the concentration is very small. Surfactant molecule can lie low on surface of solution when the concentration is very small. On the surface of concentrated solution, polar group of surfactant molecule point to the interior and apolar group tend to stay on the exterior. On the surface of concentrated solution, polar group of surfactant molecule point to the interior and apolar group tend to stay on the exterior.

When the concentration comes to a certain value, surfactant molecule hold fully on surface and form a saturated absorption layer. When the concentration comes to a certain value, surfactant molecule hold fully on surface and form a saturated absorption layer.