How about the diameter of the side oil molecules? with oil film method .

Use a syringe or dropper to drop the oleic acid alcohol solution prepared by the teacher in advance, drop it into the graduated cylinder, and write down the number of drops when a certain volume is added in the graduated cylinder, so as to calculate the volume of a drop of diluted oleic acid.

During the experiment, pour about 2cm deep water into a shallow dish with a side length of 30cm and 40cm, then sprinkle prickly heat powder or gypsum powder evenly on the water surface, and then use a syringe or dropper to drop the pre-prepared oleic acid alcohol solution on the water surface, and after the shape of the oleic acid film is stable, put the prepared glass plate on the shallow plate, and then draw the shape of the oleic acid film on the glass plate with colored pencils.

Place the glass plate on the coordinate paper and calculate the area of the oleic acid film.

The thickness is the molecular size l=nv s

n is the number of drops, v is the volume of oleic acid in each drop of oleic acid dilution, and s is the area of the oil film).

With the oil film method, it is assumed that the oil film is only one layer of molecules, as long as the volume of the oil film is known, and then the surface area is calculated, it is OK The specific operation is a bit forgotten.

With a certain volume of oil, pour it into the surface of the water, and the oil molecules are spread on the surface of the water to measure the surface area. Divide the volume by the diameter of the oil molecule by the surface area.

The first floor is not right, oleic acid molecules are easy to contact with water at one end, and difficult to contact with water at the other end, so it is easy to form a monomolecular membrane, while other molecules, such as gasoline and vegetable oil, their molecular formula determines their affinity to water, so they do not necessarily form a monolayer.

It's a courseware, take a look.

Maybe it helps.

Pour about 2 cm of water into a shallow dish, sprinkle prickly heat powder or gypsum powder evenly on the water surface, use a syringe or dropper to slowly start dripping a drop of oleic acid alcohol solution onto the water surface, the oleic acid will expand freely on the water surface into a monomolecular oil film, gently put the plexiglass cover plate on the shallow dish, use a colored pen to draw the shape of the monomolecular oleic acid film on the glass plate, and then gently remove it.

The oil film method is a method used to estimate the diameter of the molecule, similar to taking a certain amount of millet, measuring its volume v, and then spreading it flat on the table, not overlapping up and down, one grain next to another, measuring the area of these rice grains occupying the desktop s, so as to calculate the diameter of the rice grain d=v s, this is just a physical model, in fact, the shape of the molecule is very complex, not really a ball, and there are gaps between the molecules.

The principle of the oil film method to measure the molecular diameter of the experiment is to measure the diameter of a drop of oil beads d, according to the formula v=1 6 d 3 to find the volume of this drop of oil beads, Hui Qipei, drop this drop of oil beads on a larger water surface, so that its area is spread as far as possible, when it diffuses into a monolayer of oil film, measure the area of the oil film s, and then use the formula d=v s to find the thickness of the oil film d. Because it is a monolayer, the thickness of the oil film is also the diameter of the oil molecules.

The experiment of measuring the size of molecules by oil film method is not easy to do in school. For example, if an oil droplet with a diameter of 5 mm is dropped on the surface of the water, if it diffuses into a monolayer of oil film, its area is about 1 2 103 m, which is equivalent to the area of a square with a side length of 34 5 m. With such a large surface of water, ordinary schools cannot do it.

Therefore, students are not able to gain a perceptual understanding of the size of molecules measured by the oil film method.

In order to deepen my understanding of the experimental method of measuring the size of molecules by the oil film method, I arranged a simulation experiment for the students in my teaching. The method is to measure 20ml of small m with a small-caliber graduated cylinder, pour it on a piece of eight-open paper, spread out the small m into a layer, measure the area s of the side m with a scale, and then calculate the thickness of the small m layer, that is, the diameter of the small m. During the experiment, it is better to use a small-caliber cylinder (for example, the diameter is 10mm) for measuring the volume of small m, and the volume of small m is more accurate.

Experiments to determine the size of molecules by the oil film method

Experimental method: Very little oleic acid is dropped on the water surface, and the oleic acid will form a very thin oil film on the water surface that can be regarded as composed of a single layer of molecules, and the thickness of the film is measured as the diameter of the molecule

Experimental procedure: a first add alcohol to 1ml of oleic acid to 10ml of solution A, then take 1ml of solution A and add alcohol to 500ml of solution B to get it;

B suck solution B with a touch syringe, drop by drop into a small measuring cylinder, when 80 drops are dropped, the volume is measured to be 1ml;

c Sprinkle some prickly heat powder evenly on the water surface of the shallow water pan, and use a syringe to drop 1 drop of oleic acid solution B into the water surface;

Please ask the following questions:

1) The volume of pure oleic acid in one drop of oleic acid in the sail solution is ml;

2) It is known that the side length of the square grid in the figure is 1cm, then the area of the oil film is cm2;

3) Estimate the diameter of the oil molecule to be about cm

Answers to test questions. Answer] Analysis: (1) According to the question, find the macro hail volume of pure oleic acid in a drop of oleic acid solution;

2) Count the number of grids of the oil film area according to the figure, more than half a grid is counted as a grid, less than half a grid is rounded, and then the area of the oil film is calculated;

3) Knowing the volume of the oil and the area of the oil film, the diameter of the oil molecule can be found by d =

Answer: Solution: (1) The volume of pure oleic acid in a drop of oleic acid solution v= ml;

2) As can be seen from the diagram, the number of grids of the coordinate paper occupied by the oil film is 80, and the area of the oil film is s=1cm 1cm 80=80cm2;

3) the diameter of the oil molecule d===;

So the answer is: (1); （2）80（78～81）；（3）

Simulation experiment of measuring the diameter of molecules by oil film method.

In the chapter on thermal motion in high school physics, we talked about the oil film method, a rough method for determining the size of molecules. Its principle is to measure the diameter of a drop of oil bead d, according to the formula v=1 6 d 3 to find the volume of this drop of oil droplet, drop this drop of oil bead on a larger water surface, so that its area is spread as far as possible, when diffused into a monolayer oil film, measure the area of the oil film s, and then use the formula d=v s to find the thickness of the oil film d. Because it is a monolayer, the thickness of the oil film is also the diameter of the oil molecules.

Method: Liquid Steps.

Use a syringe or dropper to drop the pre-prepared oleic acid alcohol solution into the graduated cylinder drop by drop, and note the number of drops added to a certain volume in the graduated cylinder, such as how many drops are added by 1 ml. Find the volume v of pure oleic acid contained in a drop of oleic acid alcohol solution.

Pour about 2 centimeters of water into a shallow dish and sprinkle the prickly heat powder or gypsum powder evenly on the surface of the water. Don't sprinkle too much or too little, just in moderation.

Slowly drop a drop of oleic acid alcohol solution onto the surface of the water with a syringe or dropper, and the oleic acid will expand freely on the surface of the water to form a single molecule of oil.

Gently place the Plexiglass cover on a shallow plate, trace the shape of the monomolecular oleic acid film on the glass plate with a colored pencil, and gently remove it.

Place a glass plate depicting the shape of an oleic acid film on the coordinate paper. Count the number of small cells in the shape of the oleic acid film, calculate the mega-containing area s of the single-molecule oil film, and then calculate the thickness of the oil film d = v s according to the volume of pure oleic acid in a drop of oleic acid solution and the area of the oil film, that is, the diameter of the measured oleic acid molecule.

The oil film method is a method used to estimate the diameter of the sub-volume. It is similar to taking a certain amount of millet, measuring its volume v, and then spreading it flat on the tabletop, without overlapping up and down, one grain next to another, measuring the area s that these rice grains occupy on the tabletop, so as to calculate the diameter of the rice grains d=v s. It's just a physical model, and in fact, the shape of the molecule is so complex that it's not really a ball, and there are gaps between the molecules.

The molecular size was estimated by the experimental oil film method.

Experimental principle: the volume of oil drops onto the water surface, so that it is evenly and as far as possible spread into a very thin layer, at this time it can be considered that the oil molecules are closely arranged into a single layer of oil film one by one, and the thickness of the oil film is the diameter of a single molecule, so it is only necessary to measure the area of the oil film, and the approximate diameter of the oil molecule is known.

d=v friend no s

When the alcohol oleic acid solution used in the experimental process is dissolved in water, the alcohol is dissolved in water, and the oleic acid forms a single-molecule oil film

The volume of the oil droplet = the area of the oil film and the diameter of the molecule.

The volume of a drop of oil.

v = molecular diameter.

d=v/s=2×10^(-9)m^3/3m^2=

Think of the molecule as a spherical model [v score = 4 (d 2)3 3 = d 3 6]; Think of the molecule as a cube model (v score = d3); Each gas molecule is located in the center of the same cube model.

The oil film is regarded as a single-molecule oil film, and the gap between the oil molecules is not considered, the oil film molecules are regarded as spherical, and the diameter of the oil molecules is equal to the thickness of the oil film.

So d=v s

The experimental oil film method estimated the size of the Lie crack and the molecule.

Experimental principle: the volume of oil drops onto the water surface, the source cover makes it evenly and as far as possible spread into a very thin layer, at this time it can be considered that the oil molecules are closely arranged into a single layer of oil film one by one, and the thickness of the oil film is the diameter of a single molecule, so only the area of the oil film needs to be measured, and the approximate diameter of the oil molecule is known.

d=v s When the alcohol oleic acid solution used in the experimental process is dissolved in water, the alcohol is dissolved in water, and the oleic acid forms a single molecule oil film

Method:1The oil droplets are dropped into a beaker filled with water so that the oil droplets are evenly distributed on the surface of the water, so that the oil molecules are laid together one by one in a spherical form.

2.Then measure the area of the beaker mouth.

3.And then divide the volume of oil in the water by the area, and you get the diameter of the oil molecule.

Notes:1The oleic acid is not too strong, the alcohol should not be too much, and the oil film must be dispersed and must not be stained on the edge of the water tray.

2.When calculating the area, the less than half a grid on the coordinate paper is rounded off (it cannot be added to other less than half a grid) to dig back to Jane.

3.When dropping oleic acid, the dropper should not be too high from the water surface, so that the oleic acid is not easy to float on the water surface, and it cannot be too low to reach the water surface.