I would like to talk about important things that are rarely explained on the websites of companies that sell cleaning systems, but it is much more pleasant to understand what is at stake when choosing a filter for your family or for work. This overview presents some important aspects to consider when choosing a filter.

What is micron and nanometer?

If you were looking for a water filter, then most likely you came across the name "micron". When it comes to mechanical cartridges, you can often see phrases such as "the unit filters coarse particles of dirt up to 10 microns or more." But how much is 10 microns? I would like to know what kind of contamination and use a cartridge designed for 10 microns will miss. Regarding membranes (be it a flow filter or reverse osmosis), another term is used - a nanometer, which is also a difficult size to represent. One micron is 0.001 millimeters, that is, if you conditionally divide one millimeter into 1000 divisions, then we just get 1 micron. A nanometer is 0.001 micron, which is essentially one millionth of a millimeter. The names "micron" and "nanometer" are coined to simplify the representation of such small numbers.

Microns are most often used to represent the depth of filtration produced by polypropylene or carbon cartridges, nanometers to represent the level of filtration produced by ultrafiltration or reverse osmosis membranes.

How are water filters different?

There are 3 main types of filters: flow filters, flow filters with an ultrafiltration membrane (membrane) and reverse osmosis filters. What is the main difference between these systems? A flow filter can be considered basic purification, since it rarely purifies water to a drinking state - that is, unlike the other two types of filters, after running water, you need to boil water before drinking (the exceptions are systems containing Aragon, Aqualen and Ecomix material). Membrane filters - filters with an ultrafiltration membrane purify water from all types of contaminants, but leave the salt balance of water intact - that is, natural calcium, magnesium and other minerals remain in the water. The reverse osmosis system purifies water completely, including minerals, bacteria, salts - at the filter outlet, the water contains, oddly enough, only water molecules.

Chlorine is the most cunning of the water pollutants.

Generally, in order to purify water from contaminants with a membrane system, the pores of the membrane must be smaller than the dimensions of the element. However, this does not work with chlorine, since the size of its molecule is equal to the size of a water molecule, and if the pores of the membrane are made smaller than the size of chlorine, then water will not be able to pass either. Here is such a paradox. Therefore, all reverse osmosis systems as part of pre-filters and as a post-filter have carbon cartridges that thoroughly purify chlorine from water. And note, since the main " headache"Ukrainian water is exactly chlorine, if you want to buy reverse osmosis, you should choose a system with two carbon cartridges in the pre-filter - this indicates the quality of purification.

We hope the information provided has been useful to you. More information can be found on the website

And a subsection in which in general terms considered modern filtration methods based on the sieve principle. And it was hinted that membrane purifiers purify water with different quality, which depends on the size of the "cells", which are called pores, in these sieve membranes. Respectively, water microfiltration- this is the first technology from membrane water purification systems, which we will consider.

Water microfiltration - water purification at the level of large molecules (macromolecules), such as asbestos particles, paint, coal dust, protozoan cysts, bacteria, rust. Whereas macrofiltration (of water) affects sand, large silt particles, large rust particles, etc.

It can be roughly said that the particle sizes that macrofiltration filters out are particles larger than 1 micrometer (if a special one-micron cartridge is used). Whereas the particle size that microfiltration removes is particles from 1 micron to 0.1 micron.

You can ask the question: "But if particles down to 0.1 micron are removed, then why can't particles as small as 100 microns be retained using microfiltration? Why write "from 1 micron to 0.1 micron" - is this a contradiction?"

In fact, there is no particular contradiction. Indeed, microfiltration of water will remove both bacteria and huge chunks of sand. But the purpose of microfiltration is not to remove large chunks of sand. The goal of microfiltration is how to "remove particles in a specified size range". Then how would about Larger particles will simply clog the cleaner and result in additional costs.

So, let's move on to the characteristics of water microfiltration.

Since particles of 0.1-1 micron in size are removed during microfiltration, we can say that microfiltration is a membrane technology for water purification, which takes place on sieve membranes with a pore cell diameter of 0.1-1 micron. That is, on such membranes all substances that are larger than 0.5-1 microns are removed:

How completely they are removed depends on the diameter of the pores and the actual size of, say, bacteria. So, if the bacterium is long, but thin, then it will easily crawl through the pores of the microfiltration membrane. A thicker spherical bacterium will remain on the surface of the "sieve".

The most commonly used microfiltration in the food industry(for skimming milk, concentrating juices) and in medicine(for primary preparation of medicinal raw materials). Microfiltration is also used in industrial drinking water treatment- mainly in Western countries (for example, in Paris). Although there are rumors that one of the water treatment plants in Moscow also uses microfiltration technology. Maybe it's true 🙂

But there are also household filters based on microfiltration.

The most common example is track microfiltration membranes. Track from the word "track", that is, a trace, and this name is associated with how membranes of this type are made. The procedure is very simple:

1. The polymer film is bombarded by particles, which, due to their own high energy, burn traces in the film - depressions of approximately the same size, since the particles that bombard the surface have the same size.
2. Then this polymer film is etched in a solution, for example, of an acid, so that the impact marks of the particles become transparent.
3. Well, then a simple procedure for drying and fixing the polymer film on the substrate - and that's it, the track microfiltration membrane is ready!

As a result, these membranes feature a fixed pore diameter and low porosity compared to other membrane water purification systems. And the conclusion: on these membranes, particles only under a certain size will be removed.

There is also a more sophisticated version of household microfiltration membranes - microfiltration membranes coated with activated carbon . That is, the steps listed above include one more step - applying a thin layer of. These membranes remove not only bacteria and mechanical impurities, but also

• smell,
• organic matter,
• etc.

It should be taken into account that for microfiltration membranes there is a danger. Thus, bacteria that did not pass through the membrane, begin to live on this membrane and issue products of their life into purified water. That is, there is secondary water poisoning. To avoid this, follow the manufacturer's instructions for regularly disinfecting the membranes.

The second danger is that bacteria will begin to eat these membranes on their own. And they will make huge holes in them, which will let in those substances that the membrane should retain. To prevent this from happening, you should purchase filters based on a bacteria-resistant substance (eg ceramic microfiltration membranes) or be prepared for frequent replacement of microfiltration membranes.

The frequent replacement of microfiltration membranes is also spurred on by the fact that they not equipped with flushing mechanism. And the pores of the membrane are simply clogged with dirt. The membranes fail.

In principle, everything about microfiltration. Microfiltration is a fairly high-quality method of water purification. However,

The real purpose of microfiltration is not the preparation of water for drinking (due to the risk of bacterial contamination), but the preliminary preparation of water before the next stages.

The microfiltration stage removes most of the load from the subsequent stages of water treatment.

Based on materials How to choose a water filter: http://voda.blox.ua/2008/07/Kak-vybrat-filtr-dlya-vody-22.html

Molecules have sizes and various shapes. For clarity, we will depict a molecule in the form of a ball, imagining that it is covered by a spherical surface, inside which are the electron shells of its atoms (Fig. 4, a). According to modern concepts, molecules do not have a geometrically defined diameter. Therefore, it was agreed to take the distance between the centers of two molecules (Fig. 4b) as the diameter d of a molecule, so close that the forces of attraction between them are balanced by the forces of repulsion.

From the course of chemistry "it is known that a kilogram-molecule (kilomole) of any substance, regardless of its state of aggregation, contains the same number of molecules, called the Avogadro number, namely N A \u003d 6.02 * 10 26 molecules.

Now let's estimate the diameter of a molecule, for example water. To do this, we divide the volume of a kilomole of water by the Avogadro number. A kilomole of water has a mass 18 kg. Assuming that water molecules are located close to each other and its density 1000 kg / m 3, we can say that 1 kmol water occupies a volume V \u003d 0.018 m 3. Volume per molecule of water

Taking the molecule as a ball and using the ball volume formula, we calculate the approximate diameter, otherwise the linear size of the water molecule:

Copper molecule diameter 2.25*10 -10 m. The diameters of gas molecules are of the same order. For example, the diameter of a hydrogen molecule 2.47 * 10 -10 m, carbon dioxide - 3.32*10 -10 m. So the molecule has a diameter of the order 10 -10 m. On length 1 cm 100 million molecules can be located nearby.

Let's estimate the mass of a molecule, for example sugar (C 12 H 22 O 11). To do this, you need a mass of kilomoles of sugar (μ = 342.31 kg/kmol) divided by the Avogadro number, i.e., by the number of molecules in

Municipal educational institution

"Basic secondary school No. 10"

Determining the diameter of molecules

Laboratory work

Artist: Masaev Evgeniy

7th grade "A"

Head: Reznik A.V.

Guryevsky district

Introduction

In that academic year I started studying physics. I learned that the bodies that surround us are made up of tiny particles - molecules. I was wondering what the size of the molecules are. Due to their very small size, the molecules cannot be seen with the naked eye or with an ordinary microscope. I read that molecules can only be seen with an electron microscope. Scientists have proven that the molecules of different substances differ from each other, and the molecules of the same substance are the same. I wanted to measure the diameter of a molecule in practice. But unfortunately, the school curriculum does not provide for the study of problems of this kind, and it turned out to be a difficult task to consider it alone and I had to study the literature on methods for determining the diameter of molecules.

Chapter I . molecules

1.1 From the theory of the question

A molecule in the modern sense is the smallest particle of a substance that has all of its chemical properties. The molecule is capable of independent existence. It can consist of both identical atoms, for example, oxygen O 2, ozone O 3, nitrogen N 2, phosphorus P 4, sulfur S 6, etc., and from different atoms: this includes the molecules of all complex substances. The simplest molecules consist of one atom: these are molecules of inert gases - helium, neon, argon, krypton, xenon, radon. In the so-called macromolecular compounds and polymers, each molecule can consist of hundreds of thousands of atoms.

The experimental proof of the existence of molecules was the first to be most convincingly given by the French physicist J. Perrin in 1906 when studying brownian motion. It, as Perrin showed, is the result of the thermal motion of molecules - and nothing else.

The essence of a molecule can also be described from another point of view: a molecule is a stable system consisting of atomic nuclei (identical or different) and surrounding electrons, and Chemical properties molecules are determined by the outer shell electrons in the atoms. Atoms combine into molecules in most cases chemical bonds. Typically, such a bond is created by one, two, or three pairs of electrons shared by two atoms.

Atoms in molecules are connected to each other in a certain sequence and distributed in space in a certain way. Bonds between atoms have different strengths; it is estimated by the amount of energy that must be expended to break interatomic bonds.

Molecules are characterized by a certain size and shape. Different ways it was determined that 1 cm 3 of any gas under normal conditions contains about 2.7x10 19 molecules.

To understand how large this number is, we can imagine that the molecule is a "brick". Then if we take the number of bricks equal to the number of molecules in 1 cm 3 of gas under normal conditions, and tightly lay the surface of the entire globe with them, then they would cover the surface with a layer 120 m high, which is almost 4 times higher than the height of a 10-story building. A huge number of molecules per unit volume indicates a very small size of the molecules themselves. For example, the mass of a water molecule is m=29.9 x 10 -27 kg. Accordingly, the size of the molecules is also small. The diameter of a molecule is considered to be the minimum distance at which the repulsive forces allow them to approach each other. However, the concept of the size of a molecule is conditional, since at molecular distances the ideas of classical physics are not always justified. The average size of molecules is about 10-10 m.

A molecule as a system consisting of interacting electrons and nuclei can be in different states and pass from one state to another forcedly (under the influence of external influences) or spontaneously. For all molecules of this type, a certain set of states is characteristic, which can serve to identify molecules. As an independent formation, a molecule has in each state a certain set physical properties, these properties are preserved to some extent during the transition from molecules to the substance consisting of them and determine the properties of this substance. During chemical transformations, molecules of one substance exchange atoms with molecules of another substance, break up into molecules with a smaller number of atoms, and also enter into chemical reactions other types. Therefore, chemistry studies substances and their transformations in close connection with the structure and state of molecules.

A molecule is usually called an electrically neutral particle. In matter, positive ions always coexist with negative ones.

According to the number of atomic nuclei included in the molecule, diatomic, triatomic, etc. molecules are distinguished. If the number of atoms in a molecule exceeds hundreds and thousands, the molecule is called a macromolecule. The sum of the masses of all the atoms that make up the molecule is considered as the molecular weight. According to the molecular weight, all substances are conditionally divided into low and high molecular weight.

1.2 Methods for measuring the diameter of molecules

In molecular physics, the main "actors" are molecules, unimaginably small particles that make up all the substances in the world. It is clear that for the study of many phenomena it is important to know what they are, molecules. In particular, what are their sizes.

When talking about molecules, they are usually thought of as small, elastic, hard balls. Therefore, to know the size of molecules means to know their radius.

Despite the smallness molecular sizes, physicists have been able to develop many ways to determine them. Physics 7 talks about two of them. One exploits the property of some (very few) liquids to spread in the form of a film one molecule thick. In another, the particle size is determined using a complex device - an ion projector.

The structure of molecules is studied by various experimental methods. Electron diffraction, neutron diffraction, and X-ray structural analysis provide direct information about the structure of molecules. Electron diffraction, a method that investigates the scattering of electrons by a beam of molecules in the gas phase, makes it possible to calculate the parameters of the geometric configuration for isolated, relatively simple molecules. Neutron diffraction and X-ray structural analysis are limited to the analysis of the structure of molecules or individual ordered fragments in the condensed phase. X-ray studies, in addition to the indicated information, make it possible to obtain quantitative data on the spatial distribution of electron density in molecules.

Spectroscopic methods are based on the individuality of the spectra of chemical compounds, which is due to the set of states characteristic of each molecule and the corresponding energy levels. These methods make it possible to carry out qualitative and quantitative spectral analysis of substances.

Absorption or emission spectra in the microwave region of the spectrum make it possible to study transitions between rotational states, determine the moments of inertia of molecules, and, on their basis, bond lengths, bond angles, and other geometric parameters of molecules. Infrared spectroscopy, as a rule, investigates transitions between vibrational-rotational states and is widely used for spectral-analytical purposes, since many vibrational frequencies of certain structural fragments of molecules are characteristic and change little when passing from one molecule to another. At the same time, infrared spectroscopy also makes it possible to judge the equilibrium geometric configuration. The spectra of molecules in the optical and ultraviolet frequency ranges are associated mainly with transitions between electronic states. The result of their research is data on the features of potential surfaces for various states and the values ​​of molecular constants that determine these potential surfaces, as well as the lifetimes of molecules in excited states and the probabilities of transitions from one state to another.

On the details of the electronic structure of molecules, photo- and X-ray electron spectra, as well as Auger spectra, provide unique information, which makes it possible to evaluate the type of symmetry of molecular orbitals and the features of the electron density distribution. Laser spectroscopy (in various frequency ranges), which is distinguished by exceptionally high selectivity of excitation, has opened up wide possibilities for studying individual states of molecules. Pulsed laser spectroscopy makes it possible to analyze the structure of short-lived molecules and their transformation into an electromagnetic field.

A variety of information about the structure and properties of molecules is provided by the study of their behavior in external electric and magnetic fields.

There is, however, a very simple, although not the most accurate, way to calculate the radii of molecules (or atoms). It is based on the fact that the molecules of a substance, when it is in a solid or liquid state, can be considered to be tightly adjacent to each other. In this case, for a rough estimate, we can assume that the volume V some mass m substance is simply equal to the sum of the volumes of the molecules contained in it. Then we get the volume of one molecule by dividing the volume V per number of molecules N .

The number of molecules in a body of mass m as well as known

, where M- molar mass of the substance N A is Avogadro's number. Hence the volume V 0 of one molecule is determined from the equality .

This expression includes the ratio of the volume of a substance to its mass. The opposite relationship

is the density of matter, so

CHAPTER 4. INITIAL INFORMATION CLASS ON THE STRUCTURE OF SUBSTANCE

Solving problems on this topic should help students form the initial concepts of molecular structure substances.

In tasks it is necessary to consider, first of all, such facts, scientific explanation which inevitably leads to the idea that bodies are made up of tiny particles - molecules.

Next, a number of problems should be solved that give the concept of the size of molecules, as well as their properties, movement and interaction. Due to insufficient mathematical preparation of students, most of the tasks should be of high quality.

Considerable attention should also be paid to experimental problems. Students can perform simple experimental tasks at home.

The obtained information about the molecular structure of substances is then used to explain the difference between the solid, liquid and gaseous states of matter.

1. The existence of molecules. Molecule sizes

It is useful to clarify and deepen the initial concept of molecules and their sizes with the help of tasks in which photographs of molecules obtained using an electron microscope are given.

Solving problems that show the complex structure of molecules is optional. But in an introductory plan, especially in classes with strong academic performance, 2-3 tasks can be considered, showing that the molecules of complex substances consist of smaller particles - atoms.

Along with qualitative problems, it is possible to give tasks for simple calculations of the absolute and relative sizes of molecules.

43. Figure 11 shows a photograph of a particle solid body obtained with an electron microscope. Which

Rice. 11. (see scan)

conclusion can be drawn on the basis of this photograph about the structure of a solid body? Using the scale indicated in the photograph, determine the size of one particle - a molecule.

Solution. Attention is drawn to the fact that all molecules are the same, are arranged in a solid body in a certain order and have such a dense packing that only small gaps remain between them.

To determine the diameter of the molecules, their number (50) is counted at a specified distance of 0.00017 cm, and, by calculating, they find that the diameter of the molecule is approximately 0.000003 cm.

You need to tell the students that this is a giant molecule. A water molecule, for example, has a diameter about a hundred times smaller.

44. An optical microscope makes it possible to distinguish objects about 0.00003 cm in size. Is it possible to see in such a microscope a drop of water, along the diameter of which a hundred, a thousand, a million molecules fit? The diameter of a water molecule is approximately

Therefore, in an optical microscope, one can see only such a drop of water, the diameter of which is at least 1000 times larger than the diameter of a water molecule. Water molecules themselves cannot be seen with an optical microscope.

45. The number of molecules in air at normal pressure and 0°C is . Assuming that the diameter of one gas molecule is approximately 0.00000003 cm, calculate how long the “beads” would be if all these molecules could be tightly strung on an invisible thread.

Answer. 8 million km.

46(e). Dip two test tubes upside down into the water and place in them bare wires attached to the poles of the battery. Observe the gas bubbles and examine their composition with the help of a glowing splinter. Where did gases come from?

Solution. By the bright burning of a splinter in one test tube and a flash in another, it is concluded that oxygen was in one test tube, and hydrogen in the other.

They explain that gases appeared during the decomposition of a water molecule. Consequently, the properties of the molecule when it is divided into smaller parts are not preserved. Students can be told that water decomposes into oxygen and hydrogen also when water vapor is heated to a very high temperature.