As one of the natural sciences, chemistry studies. general chemistry
Chemistry is a natural science. Like other natural sciences, it studies a certain side of nature and natural phenomena. Unlike other natural sciences, chemistry pays close attention to matter. A substance is, for example, water, some metal, salt, a certain protein.
Many objects that surround us consist not of one, but of many substances. For example, a living organism consists of water, proteins, fats, carbohydrates and a number of other substances. Even substances that are homogeneous in appearance can be mixtures of different substances (for example, solutions).
The science of chemistry throughout history has made it possible not only to study the structure and properties of substances, but also to obtain new substances that were not previously in nature. These are, for example, various plastics, organic substances.
Chemistry, like mathematics, has its own formal language. The interactions of substances here are usually expressed through a certain record of chemical reactions, and the substances themselves are written in the form of formulas.
Chemistry explains many of the changes in nature. The main question that chemistry answers is why do some substances turn into others?
Chemistry is a natural science. Chemistry in the environment. Brief information from the history of chemistry
Chemistry belongs to the natural sciences. Chemistry is the science of substances, their properties and transformations. The subject of chemistry is the chemical elements and their compounds, as well as the patterns by which chemical reactions proceed. Modern chemistry is very diverse both in terms of objects and methods of their study, therefore many of its sections are independent sciences. Now the main branches of chemistry are inorganic chemistry, organic chemistry and physical chemistry. At the same time, significant sections of chemistry arose on the border with other sciences. Thus, the interaction of chemistry and physics gave, in addition to physical chemistry, chemical physics. One of the advanced areas of chemistry is biochemistry - a science that studies the chemical foundations of life. Almost every scientific study requires the use of physical methods to establish the structure of matter and mathematical methods to analyze the results.
Chemistry plays an important role in scientific and technological progress. It has found application in all branches of science, technology and production. Chemistry ensures the processing of minerals into valuable products. Chemistry has a significant impact on the productivity of agricultural production. Equally significant is the role of chemistry in the production of plastics, paints, building materials, synthetic fabrics, synthetic detergents, perfumes and pharmaceuticals. The study of chemistry helps a person not only to increase general erudition, but also to know himself and the world around him.
The term "chemistry" first appeared in a treatise by the Egyptian Greek Zosimus in 400 AD, in which Zosimus says that "chemistry" was taught to people by demons who descended to earth from heaven. The name "chemistry" comes from the word "Khemi" or "Humana", which the ancient Egyptians called their country, as well as the Nile black soil.
The first chemists were the Egyptian priests. Significant experimental material had already been collected and described in the third century BC. In the well-known library of Alexandria, there were about seven hundred handwritten books, many works on chemistry were kept. The Greek philosopher Democritus, who lived in the fifth century BC, first suggested that all bodies are made up of small, invisible, indivisible particles of solid matter that move. He called these particles "atoms". From the third century AD, the period of alchemy began in the history of chemistry, the purpose of which was to find ways to turn base metals into noble ones (silver and gold) using the philosopher's stone. In Rus', alchemy was not widespread, although the treatises of alchemists were known. At the beginning of the sixth century, alchemists began to apply their knowledge to the needs of production and treatment. During the period of the seventeenth and eighteenth centuries, experimental methods began to be used in chemical research.
The first theory of scientific chemistry was the theory of phlogiston (a weightless substance that is released from a substance during combustion of substances), proposed by G. Stahl in the eighteenth century. This theory turned out to be erroneous, although it lasted for almost a century. The French chemist A. Lavoisier and the Russian chemist M. V. Lomonosov used precise measurements in the study of chemical reactions, refuted the theory of phlogiston, and formulated the law of conservation of mass. From 1789 to 1860, the period of quantitative chemical laws (atomic and molecular science) continued. The modern stage in the development of chemical science, which began in the twentieth century, continues to the present day. Any progress in practical chemistry today is based on the achievements of fundamental science.
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Subject and tasks of chemistry. Place of chemistry among the natural sciences
Chemistry refers to the natural sciences that study the world around us. It studies the composition, properties and transformations of substances, as well as the phenomena that accompany these transformations. One of the first definitions of chemistry as a science was given by the Russian scientist M.V. Lomonosov: "Chemical science considers the properties and changes of bodies ... the composition of bodies ... explains the reason for what happens to substances during chemical transformations."
According to Mendeleev, chemistry is the study of elements and their compounds. Chemistry is closely related to other natural sciences: physics, biology, geology. Many sections of modern science arose at the intersection of these sciences: physical chemistry, geochemistry, biochemistry, as well as with other branches of science and technology. Mathematical methods are widely used in it, calculations and modeling of processes on electronic computers are used. In modern chemistry, many independent sections have emerged, the most important of which, in addition to those noted above, are inorganic chemistry, organic chemistry, chemical engineering. polymers, analytical chemistry, electrochemistry, colloid chemistry and others. The object of study of chemistry are substances. They are usually divided into mixtures and pure substances. Among the latter, simple and complex are distinguished. More than 400 simple substances are known, and much more complex substances: several hundred thousand, related to inorganic, and several million organic. The chemistry course studied in high school can be divided into three main parts: general, inorganic and organic chemistry. General chemistry considers the basic chemical concepts, as well as the most important patterns associated with chemical transformations. This section includes the basics from various sections of modern science: “physical chemistry, chemical kinetics, electrochemistry, structural chemistry, etc. Inorganic chemistry studies the properties and transformations of inorganic (mineral) substances. Organic chemistry from. properties and transformations of organic substances.
Basic concepts of analytical chemistry (analytics)
analytical chemistry spectral photometric
Analytical chemistry occupies a special place in the system of sciences. With its help, scientists accumulate and verify scientific facts, establish new rules and laws.
Chemical analysis is necessary for the successful development of such sciences as biochemistry and physiology of plants and animals, soil science, agriculture, agrochemistry, microbiology, geochemistry, and mineralogy. The role of analytical chemistry in the study of natural sources of raw materials is constantly growing. Analytical chemists continuously monitor the operation of technological lines and the quality of products in the food, pharmaceutical, chemical, nuclear and other industries.
Chemical analysis based on the fundamental laws of general chemistry. Therefore, in order to master analytical methods, it is necessary to know the properties of aqueous solutions, the acid-base and redox properties of substances, complexation reactions, the patterns of formation of precipitates and colloidal systems.
(Analytical chemistry, or analytics, is a branch of chemical science that develops, on the basis of the fundamental laws of chemistry and physics, fundamental methods and techniques for qualitative and quantitative analysis of the atomic, molecular and phase composition of a substance.
Analytical chemistry is the science of determining the chemical composition, methods of identifying chemical compounds, principles and methods for determining the chemical composition of a substance and its structure.
The analysis of a substance means obtaining empirically data on the chemical composition of a substance by any methods - physical, chemical, physico-chemical.
It is necessary to distinguish between the method and methodology of analysis. The method of analysis of a substance is a brief definition of the principles underlying the analysis of a substance. Method of analysis - a detailed description of all conditions and operations that provide regulated characteristics, including - the correctness and reproducibility of the results of the analysis.
Establishing the chemical composition is reduced to solving the problem: what substances are included in the composition of the studied, and in what quantity.
Modern analytical chemistry (analytics) includes two sections
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Qualitative chemical analysis is the determination (discovery) of chemical elements, ions, atoms, atomic groups, molecules in the analyzed substance.
Quantitative chemical analysis is the determination of the quantitative composition of a substance, i.e., the determination of the number of chemical elements, ions, atoms, atomic groups, molecules in the analyzed substance. It is possible to give another (equivalent) definition of quantitative analysis, reflecting not only its content, but also the final result, namely: quantitative analysis of a substance is an experimental determination (measurement) of the concentration (quantity) of chemical elements (compounds) or their forms in the analyzed substance, expressed as the boundaries of the confidence interval or a number with an indication of the standard deviation.
Any method of analysis uses a certain analytical signal- chemical, physico-chemical, physical parameter that characterizes a certain property of the substance under study. For this reason, all methods the nature of the measured property or the method of recording the analytical signal usually divided into three large groups:
Groups of analysis methods.
1) chemical methods of analysis - when data are obtained as a result of precipitation, gas evolution, color change;
2) physico-chemical methods of analysis - any physical or chemical change in quantities can be recorded;
3) physical methods of analysis
Instrumental (physical and physico-chemical) methods of analysis -- methods based on the use of dependencies between the measured physical properties of substances and their qualitative and quantitative composition.
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Chemical (or classic) |
Methods that use analytical signals in the course of chemical reactions. Such signals are precipitation, gas evolution, formation of complex compounds, color change, etc. Chemical methods include qualitative systematic analysis of cations and anions, as well as chemical quantitative methods - gravimetry (weight analysis), titrimetry (volume analysis). |
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Physico-chemical |
Chemical reactions are also used, but physical phenomena are used as an analytical signal. These methods include: electrochemical, photometric, chromatographic, kinetic. |
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Physical |
They do not require chemical reactions, but study the physical properties of a substance in such a way that the analytical signal is related to its nature and quantity. These are optical spectra of emission, absorption, x-ray, magnetic resonance. |
To chemical methods include:
Gravimetric (weight) analysis
Titrimetric (volume) analysis
Gas volumetric analysis
To physical and chemical methods include all methods of instrumental analysis:
Photocolorimetric
Spectrophotometric
Nephelometric
Potentiometric
Conductometric
polarographic
To physical include:
Spectral emission
Radiometric (tagged atom method)
X-ray spectral
Luminescent
neutron activation
Emission (flame photometry)
Atomic absorption
Nuclear magnetic resonance
Fphysical-chemical methods of analysis
Physico-chemical methods are based on carrying out analytical reactions, the end of which is determined using instruments.
The devices measure the change in light absorption, electrical conductivity and other physicochemical properties of substances, depending on the concentration of the analyte. The result is recorded on the recorder's lepto, digital scoreboard or in some other way.
When performing analyzes, along with relatively simple equipment, devices with complex optical and electronic circuits are used. Hence the common name of these methods -- instrumental methods of analysis.
Instrumental methods, as a rule, are characterized by high sensitivity, selectivity, speed of analysis, the use of small amounts of test substances, objectivity of the results, the possibility of automating the process of analysis and processing the information obtained using a computer. Many determinations are fundamentally feasible only by instrumental methods and have no analogues in traditional gravimetric and titrimetric methods.
This applies to the quantitative separation and identification of components, the determination of the group and individual composition of complex multicomponent mixtures, the analysis of trace impurities, the determination of the structure of substances, and other complex problems of the analytical chemistry of oils and petroleum products.
The following groups of instrumental methods of analysis are of the greatest practical importance.
Spectral methods
These methods of analysis are based on the use of the phenomena of emission of electromagnetic radiation by atoms or molecules of the substance being determined or interaction (most often absorption) of electromagnetic radiation by atoms or molecules of a substance.
The emission or absorption of electromagnetic radiation leads to a change in the internal energy of atoms and molecules. The state with the lowest possible internal energy is called the ground state, all other states are called excited states. The transition of an atom or molecule from one state to another is always accompanied by an abrupt change in energy, i.e., receiving or giving away a portion (quantum) of energy.
The quanta of electromagnetic radiation are photons, the energy of which is related to the frequency and wavelength of the radiation.
The set of photons emitted or absorbed during the transition of an atom or molecule from one energy state to another is called a spectral line. If all the energy of this radiation is concentrated in a sufficiently narrow range of wavelengths, which can be characterized by the value of one wavelength, then such radiation and the corresponding spectral line are called monochromatic.
The set of wavelengths of electromagnetic radiation (spectral lines) related to a particular atom (molecule) is called the spectrum of a given atom (molecule). If the energy of the initial state E 1 is greater than the energy of the final state E 2 between which the transition occurs, the resulting spectrum is an emission spectrum; if E 1 The nature of the interaction of quanta so different in energy with matter is fundamentally different. Thus, the emission of y-quanta is associated with nuclear processes, the emission of quanta in the X-ray range is due to electronic transitions in the inner electronic layers of the atom, the emission of UV and visible radiation quanta or the interaction of matter with them is a consequence of the transition of external valence electrons (this is the field of optical methods of analysis) the absorption of IR and microwave quanta is associated with the transition between the vibrational and rotational levels of molecules, and the radiation in the radio wave range is due to transitions with a change in the orientation of the spins of electrons or atomic nuclei. Using the standard row method, take a row of colorimetric tubes with ground stoppers, prepare a constant standard row of colored solutions containing successively increasing amounts of the standard solution. It turns out the so-called standard series or colorimetric scale (exemplary scale). You can use a set of specially selected colored glasses. The absorption coefficient K determines the structure of the absorbing compound. The absolute value of K depends on the method of expressing the concentration of a substance in a solution and the thickness of the absorbing layer. If the concentration is expressed in mol / dm 3, and the layer thickness is in cm, then the absorption coefficient is called the molar extinction coefficient e: at c \u003d 1M and 1 \u003d 1 cm b \u003d A, i.e., the molar extinction coefficient is numerically equal to the optical density of the solution with concentration 1M, placed in a cuvette with a layer thickness of 1 cm. For photometric analysis, the absorption of light in the ultraviolet (UV), visible and infrared (IR) regions of the spectrum is of greatest importance. Colorless sunlight, the so-called white light, passing through a prism, is decomposed into several colored rays. Rays of different colors have different wavelengths. The wavelength of a monochromatic beam, that is, a beam of a certain color, is measured in nanometers (nm) or micrometers (µm). The visible part of the spectrum includes rays with a wavelength X from 400 to 760 nm. Rays with a wavelength of 100 to 400 nm form the invisible ultraviolet part of the spectrum, rays with a wavelength of more than 760 nm form the infrared part of the spectrum. For many analytical determinations, it is sufficient to single out a spectral band with a width of 20 to 100 nm. This is achieved with the help of light filters that have selective absorption of radiant energy and transmit light in a fairly narrow wavelength range. Most often, glass filters are used, and the color of the filter corresponds to the part of the spectrum that this filter transmits. As a rule, instruments for colorimetric analysis are equipped with a set of light filters that increase the accuracy and sensitivity of quantitative analysis methods. If the max of the analyzed solution is not exactly known, the light filter is chosen as follows: the optical density of the solution is measured by introducing all the light filters sequentially; measurement is carried out relative to distilled water. The light filter, when using which the highest optical density is obtained, is considered the most suitable for further work. Any determination using the photometric method of analysis consists of two stages: transferring the analyte to a colored state and measuring the optical density of the solution. The reactions of complexation are of the greatest importance at the first stage. In the case of strong complexes, a small excess of the complexing agent is sufficient for complete binding of the analyte. However, intensely colored, but low-strength complexes are often used. In the general case, it is necessary to create such an excess of the reagent in the solution so that its concentration is not less than 10.K (K is the instability constant of the complex). In most cases (for dilute solutions), the calibration graph is expressed as a straight line passing through the origin. Often there are deviations from the straight line in a positive or negative direction; the reason for this may be the complex nature of the spectrum of the colored compound, which leads to a change in the absorption coefficient in the selected wavelength range with a change in the concentration of the solution. This effect is eliminated when monochromatic light is used, i.e. when working on spectrophotometers. It should be borne in mind that the observance of the Bouguer-Lambert-Beer law, i.e. the rectilinear nature of the calibration curve is not a prerequisite for successful quantification. If, under certain conditions, a non-linear dependence of D on c is established, then it can still serve as a calibration curve. The concentration of the analyte can be determined from this curve, but its construction requires a larger number of standard solutions. However, the linear dependence of the calibration curve increases the accuracy of the determination. In practice, they proceed as follows: fill a cuvette of medium thickness (2 or 3 cm) with a solution with a concentration corresponding to the middle of a series of standard solutions, and use it to select the optimal wavelength (or optimal light filter). If the optical density obtained in this case for the region of maximum absorption of the system under study corresponds approximately to the middle of the optimal interval (0.40.5), then this means that the cuvette was chosen successfully; if it goes beyond the boundaries of this intersal or is close to them, then you need to change the cuvette by increasing or decreasing its thickness. Subject to the law of Bouguer - Lambert - Beer, in the case when, when measuring the latter in a series of standard solutions, optical density values > 1.0 are obtained, it is possible to measure optical densities in a cuvette with a smaller layer thickness and, having converted to the layer thickness, at which the densities of the first solutions were measured, put them on one graph of the dependence D = f(c). Among the optical methods of analysis, we also consider the refractometric method based on the ability of various substances to refract transmitted light in different ways. This method is one of the simplest instrumental, requires small amounts of the analyte, the measurement is carried out in a very short time. This method can identify liquid substances by their refractive index of light, determine the content of a substance in a solution (for those substances whose refractive index differs markedly from the refractive index of the solvent). The refractive index is a property of oil fractions and oil products, which must be determined in laboratories during their adsorption separation. As can be seen from the data in Table. 3.1, the refractive indices measured at different temperatures are different. Therefore, in addition to the index showing the wavelength of the incident light, the refractive index designation includes an index showing the temperature during measurement: for example, n D 20 means that the refractive index was measured at a temperature of 20 ° C and a wavelength of light 589 nm yellow. The refractive index of liquid petroleum products is determined as follows. Before measuring the refractive index, the working surfaces of the prisms of the refractometer are thoroughly washed with spirit and distilled water. Then, the correctness of the scale setting is checked against the quotation fluid (i.e., a fluid with a known refractive index). Most often, distilled water is used, for which I c 20 \u003d 1.3330. Then the working surfaces of the prisms are wiped dry and 2–3 drops of the analyte are added to the prism chamber. By rotating the mirror, the light flux is directed into the window of the lighting chamber and the appearance of the illuminated field is observed through the eyepiece. By rotating the prism chamber, the border of light and shadow is introduced into the field of view, and then, using the handle of the dispersion compensator, a clear uncolored border is achieved. Carefully rotating the prism camera, point the border of light and shadow at the center of the sighting cross and read the refractive index through the magnifying glass of the reading scale. Then they shift the border of chiaroscuro, again combine it with the center of the sighting cross and make a second count. Three readings are taken, after which the working surfaces of the prisms are washed and wiped with a lint-free cloth, the analyte is added again, a second series of measurements is taken, and the average value of the refractive index is calculated. Electrochemical is a group of instrumental methods based on the existence of a relationship between the composition of the analyte and its electrochemical properties. Electrical parameters (current strength, voltage, resistance) depend on the concentration, nature and structure of the substance involved in the electrode (electrochemical) reaction or in the electrochemical process of charge transfer between the electrodes. Conductometry refers to electrochemical methods based on measuring the electrical conductivity of electrolyte solutions under certain conditions, depending on the concentration of the solution of the analyte. This is the basis of the direct conductometric method of analysis, which consists in directly measuring the electrical conductivity of aqueous solutions of electrolytes in comparison with the electrical conductivity of solutions of the same composition, the concentration of which is known. Typically, the direct conductometric method is used to analyze solutions containing a single electrolyte in automatic production control processes. Polarography is an analysis method based on measuring the current strength, which varies depending on the voltage during electrolysis, in conditions where one of the electrodes (cathode) has a very small surface, and the other (anode) has a large one. The current strength at which a complete discharge of all analyte ions entering the near-electrode space due to diffusion (limiting diffusion current) is achieved is proportional to the initial concentration of the analyte in solution. The main advantage of the potentiometric method in comparison with other electrochemical methods of analysis is the speed and simplicity of measurements. Using microelectrodes, it is possible to carry out measurements in samples up to tenths of a millimeter. The potentiometric method makes it possible to carry out determinations in cloudy, colored, viscous products, while excluding the operations of filtration and distillation. The interval for determining the content of components in various objects is in the range from 0 to 14 pH for glass electrodes. One of the advantages of the potentiometric titration method is the possibility of its complete or partial automation. It is possible to automate the supply of titrant, recording the titration curve, turning off the supply of titrant at a given moment of titration, corresponding to the equivalence point. Indicator electrodes In potentiometry, a galvanic cell is usually used, which includes two electrodes that can be immersed in the same solution (cell without transfer) or in two solutions of different composition, having liquid contact with each other (transfer circuit). E.d. With. galvanic cell is equal to the potential characterizing the composition of the solution. Potentiometric analysis is used to directly determine the activity of ions in solution (direct potentiometry - ionometry), as well as to indicate the equivalence point during titration by changing the potential of the indicator electrode during titration (potentiometric titration). In potentiometric titration, iscc types of chemical reactions can be used, during which the concentration of potential-determining ions changes: acid-base interaction (neutralization), oxidation-reduction, precipitation and complexation. During the titration, the emf is measured and recorded. With. cells after adding each portion of the titrant. At the beginning, the titrant is added in small portions, when approaching the end point (a sharp change in potential when a small portion of the reagent is added), the portions are reduced. To determine the end point of a potentiometric titration, you can use a tabular way of recording titration results or a graphical one. The potentiometric titration curve represents the dependence of the electrode potential on the volume of the titrant. The inflection point on the curve corresponds to the end point of the titration. A glass electrode is a conventional name for a system that includes a small vessel made of insulating glass, to the bottom of which is soldered a ball of special electrode glass, which has good electrical conductivity. Pour the standard solution into the vessel. Such an electrode is equipped with a current collector. As an internal standard solution in a glass electrode, a 0.1 M solution of HCl with the addition of sodium or potassium chloride is used. You can also use any buffer solution with the addition of chlorides or bromides. The current collector is a silver chloride electrode, which is a silver wire coated with silver chloride. An insulated, shielded wire is soldered to the down conductor. The potential of the glass electrode is due to the exchange of alkali metal ions in the glass with hydrogen ions from the solution. The energy state of ions in glass and solution is different, which leads to the fact that the surface of the glass and the solution acquire opposite charges, a potential difference arises between the glass and the solution, the value of which depends on the pH of the solution. solid electrodes. As a sensitive element of an ion-selective electrode with a solid membrane, compounds with ionic, electronic or electron-ionic conductivity at room temperature are used. There are few such connections. Typically, in such compounds (AgCl, Ag 2 S, Cu 2-x S, LaF 3), only one of the ions of the crystal lattice, which has the smallest charge and ionic radius, participates in the charge transfer process. This ensures high selectivity of the electrode. They produce electrodes sensitive to ions F -, Cl -, Cu 2+, etc. The solid-membrane design is also used in liquid-based non-selective electrodes. The industry produces film plasticized electrodes of the type EM-C1O 4 - -01, EM-NO3 - -01. The sensitive element of such electrodes consists of an electrode-active compound (complex metal compounds, ionic associates of organic and metal-containing cations and anions can be used), polyvinyl chloride and a solvent (plasticizer). Instead of a solid membrane, a plasticized membrane is glued into the electrode body, and a reference solution is poured into the electrode - 0.1 M potassium chloride solution and 0.1 M salt solution of the measured ion. A silver chloride half cell is used as a current collector. Before work, plasticized film electrodes are soaked for a day in the analyzed solution. Evaporation of the plasticizer from the surface of the electrode leads to its failure. Reference electrodes. As reference electrodes, the silver chloride electrode (Ag, AgCl / KCI) is most common, which is made by electrolytically applying silver chloride to a silver wire. The electrode is immersed in a solution of potassium chloride, which is located in vessels connected by a salt bridge with the analyzed solution. When working with a silver chloride electrode, it is necessary to ensure that the inner vessel is filled with a saturated solution of KC1. The potential of the silver chloride electrode is constant and does not depend on the composition of the analyzed solution. The constancy of the potential of the reference electrode is achieved by maintaining a constant concentration of substances in the contacting internal solution, to which the electrode reacts. In addition to the silver chloride electrode, a calomel electrode is used as a reference electrode. It is a system of metallic mercury - a solution of calomel in a solution of potassium chloride. If a saturated potassium chloride solution is used, the electrode is called a saturated calomel electrode. Structurally, this electrode is a narrow glass tube closed from below by a porous partition. The tube is filled with mercury and calomel paste. The tube is soldered into a glass vessel into which a solution of potassium chloride is poured. The reference electrodes are immersed in the analyzed solution together with the indicator electrodes. Potentiometers are used to measure the potential during potentiometric titration or the pH value. Such devices are called pH meters, as they are designed to measure the potentials of electrode systems containing a pH-sensitive high-resistance glass electrode. The instrument scale is calibrated both in millivolts and in pH units. In laboratory practice, pH-meters pH-121, pH-340, EV-74 ionomer are used (see Fig. 1.19). pH meters can be used in conjunction with automatic titrators, such as the BAT-15 type, which include a system of burettes with electromagnetic valves to control the titrant flow or a syringe, the plunger of which is driven by an electric motor connected to a micrometer. During the operation of the instruments, they are calibrated using control solutions, which are used as standard buffer solutions. For verification of pH meters, special sets of solutions are produced in the form of fixanals, designed to prepare 1 dm 3 of a buffer solution. You need to check the device for freshly prepared solutions. In potentiometric titration, conventional titrimetric analysis techniques are used to determine the concentration of the analyzed ion. The main requirement is that when the titrant is added, some ion is introduced or bound, for the registration of which there is a suitable electrode. Another condition for obtaining satisfactory results. Each laboratory worker must remember that only knowledge of safety regulations cannot completely eliminate possible accidents. Most accidents occur as a result of the fact that the worker, having made sure that accidental negligence does not always lead to an accident, begins to be less attentive to the observance of safety measures. Each enterprise, each laboratory develops detailed instructions that establish the rules for taking and storing samples, performing analytical work when testing petroleum products. Without passing the exam on these instructions, taking into account the specifics and nature of the work, as well as the requirements of the instructions establishing the general rules for working in chemical laboratories, no one can be allowed to work independently in the laboratory. During analytical work, clean towels should always be used to dry dishes. When working with substances that act on the skin (acids, alkalis, leaded gasoline, etc.), it is necessary to use rubber gloves, which must be powdered with talc before putting on, and after work, washed with water and sprinkled with talc inside and out. Poisonous substances can act on the respiratory organs and skin. In some cases, poisoning manifests itself immediately, but a laboratory worker must remember that sometimes the harmful effect of toxic substances only affects after some time (for example, when inhaling mercury vapor, leaded gasoline, benzene, etc.). These substances cause slow poisoning, which is dangerous because the victim does not immediately take the necessary medical measures. Everyone working with harmful substances must undergo an annual medical examination, and anyone working with especially harmful substances every 3-6 months. Work, accompanied by the release of toxic vapors and gases, must be carried out in a fume hood. The laboratory room must be equipped with supply and exhaust ventilation with lower and upper suction, which ensures a uniform supply of fresh air and removal of contaminated air. The doors of the cabinet must be lowered during the analysis. If necessary, they are allowed to be raised no higher than 1/3 of the total height. Analyzes of leaded gasolines, evaporation of gasolines in the determination of actual resins, washing of precipitates with gasoline and benzene, operations related to the determination of coke and ash, etc., must be carried out in a fume hood. Acids, solvents and other harmful substances should also be stored there. Places contaminated with spilled ethylated petroleum products are neutralized as follows. First, they are covered with sawdust, which are then carefully collected, taken out, doused with kerosene and burned in a specially designated place, then a layer of a degasser is applied to the entire affected surface and washed off with water. Overalls doused with leaded gasoline must be immediately removed and handed over for disposal. As degassers, a 1.5% solution of dichloramine in gasoline or bleach in the form of a freshly prepared slurry is used, consisting of one part of bleach and three to five parts of water. Kerosene and gasoline are not degassers - they only wash off the ethylated product and reduce the concentration of ethyl liquid in it. Laboratories that analyze leaded gasolines must be equipped with a supply of degassers, tanks with kerosene, showers or washbasins with warm water. Only those employees who have passed the technical minimum for the handling of leaded petroleum products and have passed a periodic medical examination may be allowed to work with leaded products in the laboratory. It is strictly forbidden to dispose of water-immiscible liquids and solids, as well as strong poisons, including mercury or its salts, into sinks. Waste of this kind should be taken out at the end of the working day to specially designated places for draining. In emergency situations, when the laboratory room is poisoned by toxic vapors or gases, it is possible to stay in it to turn off the equipment, clean up spilled solvent, etc. only in a gas mask. A gas mask should always be at the workplace and be ready for immediate use. Theoretical basis of analytical chemistry. Spectral methods of analysis. Interrelation of analytical chemistry with sciences and industries. The value of analytical chemistry. Application of precise methods of chemical analysis. Complex compounds of metals. abstract, added 07/24/2008 The concept of analysis in chemistry. Types, stages of analysis and methods: chemical (masking, precipitation, coprecipitation), physical (stripping, distillation, sublimation) and physicochemical (extraction, sorption, ion exchange, chromatography, electrolysis, electrophoresis). abstract, added 01/23/2009 The concept of quantitative and qualitative composition in analytical chemistry. Influence of the amount of substance on the type of analysis. Chemical, physical, physicochemical, biological methods for determining its composition. Methods and main stages of chemical analysis. presentation, added 09/01/2016 Practical value of analytical chemistry. Chemical, physico-chemical and physical methods of analysis. Preparation of an unknown substance for chemical analysis. Problems of qualitative analysis. Stages of systematic analysis. Detection of cations and anions. abstract, added 10/05/2011 Specificity of analytical chemistry of wastewater, preparatory work in the analysis. Concentration methods: adsorption, evaporation, freezing, release of volatile substances by evaporation. The main problems and directions of development of analytical chemistry of wastewater. abstract, added 12/08/2012 The main stages in the development of chemistry. Alchemy as a phenomenon of medieval culture. The emergence and development of scientific chemistry. Origins of chemistry. Lavoisier: a revolution in chemistry. The victory of atomic and molecular science. The origin of modern chemistry and its problems in the XXI century. abstract, added 11/20/2006 "Assay art" and the history of the emergence of laboratories. Creative development of Western European chemical science. Lomonosov M.V. as an analytical chemist. Russian achievements in the field of chemical analysis in the XVIII-XIX centuries. The development of domestic chemistry in the XX century. term paper, added 10/26/2013 Ways of knowledge and classification of modern sciences, the relationship of chemistry and physics. The structure and properties of matter as general questions of chemical science. Features of the variety of chemical structures and the theory of quantum chemistry. Mixtures, equivalent and amount of substance. lecture, added 10/18/2013 Basic functions of chemistry. Properties of detergents and cleaners. The use of chemistry in health care and education. Ensuring the growth of production, extending the shelf life of agricultural products and improving the efficiency of animal husbandry with the help of chemistry. presentation, added 12/20/2009 Methods of analytical chemistry, quantitative and qualitative analysis. Redox systems. Ways of expressing the concentration of solutions and their relationship. Classification of methods of titrimetric analysis. Molecular spectral analysis. Science is one of the most important areas of human activity at the present stage of development of world civilization. Today there are hundreds of different disciplines: technical, social, humanitarian, natural sciences. What are they studying? How did natural science develop in the historical aspect? What is natural science? When did it originate and what directions does it consist of? Natural science is a discipline that studies natural phenomena and phenomena that are external to the subject of research (man). The term "natural science" in Russian comes from the word "nature", which is a synonym for the word "nature". The foundation of natural science can be considered mathematics, as well as philosophy. By and large, all modern natural sciences came out of them. At first, naturalists tried to answer all questions concerning nature and its various manifestations. Then, as the subject of research became more complex, natural science began to break up into separate disciplines, which over time became more and more isolated. In the context of modern times, natural science is a complex of scientific disciplines about nature, taken in their close relationship. The development of the natural sciences took place gradually. However, human interest in natural phenomena manifested itself in antiquity. Naturphilosophy (in fact, science) actively developed in Ancient Greece. Ancient thinkers, with the help of primitive methods of research and, at times, intuition, were able to make a number of scientific discoveries and important assumptions. Even then, natural philosophers were sure that the Earth revolves around the Sun, they could explain solar and lunar eclipses, and quite accurately measured the parameters of our planet. In the Middle Ages, the development of natural science slowed down noticeably and was heavily dependent on the church. Many scientists at that time were persecuted for the so-called heterodoxy. All scientific research and research, in fact, came down to the interpretation and substantiation of the scriptures. Nevertheless, in the era of the Middle Ages, logic and theory developed significantly. It is also worth noting that at this time the center of natural philosophy (the direct study of natural phenomena) geographically shifted towards the Arab-Muslim region. In Europe, the rapid development of natural science begins (resumes) only in the 17th-18th centuries. This is a time of large-scale accumulation of factual knowledge and empirical material (results of "field" observations and experiments). The natural sciences of the 18th century are also based in their research on the results of numerous geographical expeditions, voyages, and studies of newly discovered lands. In the 19th century, logic and theoretical thinking again came to the fore. At this time, scientists are actively processing all the collected facts, putting forward various theories, formulating patterns. Thales, Eratosthenes, Pythagoras, Claudius Ptolemy, Archimedes, Galileo Galilei, Rene Descartes, Blaise Pascal, Nikola Tesla, Mikhail Lomonosov and many other famous scientists should be referred to the most outstanding naturalists in the history of world science. The basic natural sciences include: mathematics (which is also often called the "queen of sciences"), chemistry, physics, biology. The problem of classification of natural science has existed for a long time and worries the minds of more than a dozen scientists and theorists. This dilemma was best handled by Friedrich Engels, a German philosopher and scientist who is better known as a close friend of Karl Marx and co-author of his most famous work called Capital. He was able to distinguish two main principles (approaches) of the typology of scientific disciplines: this is an objective approach, as well as the principle of development. The most detailed was offered by the Soviet methodologist Bonifatiy Kedrov. It has not lost its relevance even today. The whole complex of scientific disciplines is usually divided into three large groups: Nature is studied by the latter. The full list of natural sciences is presented below: As for mathematics, scientists do not have a common opinion as to which group of scientific disciplines it should be attributed. Some consider it a natural science, others an exact one. Some methodologists include mathematics in a separate class of so-called formal (or abstract) sciences. Chemistry is a vast area of natural science, the main object of study of which is matter, its properties and structure. This science also considers objects at the atomic-molecular level. It also studies chemical bonds and reactions that occur when different structural particles of a substance interact. For the first time, the theory that all natural bodies consist of smaller (not visible to humans) elements was put forward by the ancient Greek philosopher Democritus. He suggested that every substance includes smaller particles, just as words are made up of different letters. Modern chemistry is a complex science that includes several dozen disciplines. These are inorganic and organic chemistry, biochemistry, geochemistry, even cosmochemistry. Physics is one of the oldest sciences on earth. The laws discovered by it are the basis, the foundation for the entire system of disciplines of natural science. The term "physics" was first used by Aristotle. In those distant times, it was practically identical philosophy. Physics began to turn into an independent science only in the 16th century. Today, physics is understood as a science that studies matter, its structure and movement, as well as the general laws of nature. There are several main sections in its structure. These are classical mechanics, thermodynamics, the theory of relativity and some others. The demarcation between the natural and human sciences ran like a thick line through the "body" of the once unified geographical science, dividing its individual disciplines. Thus, physical geography (as opposed to economic and social) found itself in the bosom of natural science. This science studies the geographic shell of the Earth as a whole, as well as individual natural components and systems that make up its composition. Modern physical geography consists of a number of them: Humanities, natural sciences - are they as far apart as it might seem? Of course, these disciplines differ in the object of research. The natural sciences study nature, the humanities focus their attention on man and society. The humanities cannot compete with the natural disciplines in accuracy, they are not able to mathematically prove their theories and confirm hypotheses. On the other hand, these sciences are closely related, intertwined with each other. Especially in the 21st century. So, mathematics has long been introduced into literature and music, physics and chemistry - into art, psychology - into social geography and economics, and so on. In addition, it has long become obvious that many important discoveries are made just at the junction of several scientific disciplines, which, at first glance, have absolutely nothing in common. Natural science is a branch of science that studies natural phenomena, processes and phenomena. There are a huge number of such disciplines: physics, mathematics and biology, geography and astronomy. The natural sciences, despite numerous differences in the subject and methods of research, are closely related to social and humanitarian disciplines. This connection is especially strong in the 21st century, when all the sciences converge and intertwine.Transitions and corresponding spectral lines passing from or to the ground state are called resonant.
When quanta are emitted or absorbed by the analyzed system, characteristic signals appear that carry information about the qualitative and quantitative composition of the substance under study.
The frequency (wavelength) of radiation is determined by the composition of the substance. The intensity of the spectral line (analytical signal) is proportional to the number of particles that caused its appearance, i.e., the amount of the substance or component of a complex mixture being determined.
Spectral methods provide ample opportunities for studying the corresponding analytical signals in various regions of the electromagnetic radiation spectrum: these are rays, x-rays, ultraviolet (UV), optical and infrared (IR) radiation, as well as microwave and radio waves.
The energy of quanta of the listed types of radiation covers a very wide range - from 10 8 to 10 6 eV, corresponding to the frequency range from 10 20 to 10 6 Hz.
Currently, a number of analysis methods are used quite widely only in research laboratories. These include:
the method of electron paramagnetic resonance (EPR), based on the phenomenon of resonant absorption by certain atoms, molecules or radicals of electromagnetic waves (a device for determining - a radio spectrometer);
nuclear magnetic resonance (NMR) method, which uses the phenomenon of absorption of electromagnetic waves by a substance due to nuclear magnetism (determination device - nuclear magnetic resonance spectrometer, NMR spectrometer);
radiometric methods based on the use of radioactive isotopes and measurement of radioactive radiation;
methods of atomic spectroscopy (atomic emission spectral analysis, atomic emission photometry of a flame, atomic absorption spectrophotometry), based on the ability of the atoms of each element under certain conditions to emit waves of a certain length - or absorb them;
mass spectrometric methods based on the determination of the masses of individual ionized atoms, molecules and radicals after their separation as a result of the combined action of electric and magnetic fields (a device for determination is a mass spectrometer).
Difficulties in instrumentation, complexity of operation, as well as the lack of standardized test methods hinder the use of the above methods in laboratories that control the quality of commercial petroleum products.
Photometric methods
Optical, the so-called photometric methods of analysis, based on the ability of atoms and molecules to absorb electromagnetic radiation, have received the greatest practical distribution.
The concentration of a substance in a solution is determined by the degree of absorption of the light flux that has passed through the solution.
In the colorimetric method of analysis, the absorption of light rays in wide areas of the visible spectrum or the entire visible spectrum (white light) is measured by colored solutions.
The spectrophotometric method measures the absorption of monochromatic light. This complicates the design of instruments, but provides greater analytical capabilities compared to the colorimetric method.
The color intensity of a solution can be determined visually (colorimetry) or with photocells (photocolorimetry).
Most of the visual methods for comparing absorbance intensity are based on different ways of equalizing the color intensity of the two compared solutions. This can be achieved by changing the concentration (dilution methods, standard series, colorimetric titration methods) or by changing the thickness of the absorbing layer (equalization method).
This method underlies the determination of the color of petroleum products on a scale of standard colored glasses. Devices - colorimeters type KNS-1, KNS-2, TsNT (see Ch. 1).
It is also possible to equalize the intensities of radiation fluxes when comparing them by changing the width of the diaphragm slit located on the path of one of the two streams being compared. This method is used in more accurate and objective methods for measuring the color intensity of a solution in photocolorimetry and spectrophotometry.
For this, photoelectrocolorimeters and spectrophotometers are used.
The quantitative determination of the concentration of a colored compound by the degree of absorption is based on the Bouguer - Lambert - Beer law:
The scales of photometric instruments are graduated in terms of absorption A and transmission T of the medium.
Theoretically, A varies from 0 to °°, and T - from 0 to 1. But with sufficient accuracy, the value of A can be measured in a very narrow range of values - approximately 0.1-g-1.0.
By measuring the absorption of a given system of monochromatic radiations of various wavelengths, one can obtain the absorption spectrum, i.e., the dependence of light absorption on the wavelength. The logarithm of the ratio I 0 /I is also called optical density and is sometimes denoted D.
For quantitative analysis, it is more convenient to carry out measurements in the UV and visible parts of the spectrum, in which even complex compounds usually have one or a small number of absorption bands (i.e., frequency ranges of light waves in which absorption of light is observed).
For each absorbing substance, one can choose a wavelength at which the most intense absorption of light rays occurs (the greatest absorption). This wavelength is denoted by max
If the area of maximum absorption max of the analyzed solution is known, then choose a light filter with a maximum transmission area close to max
This is how they do it when working on photoelectrocolorimeters.
Photoelectrocolorimeters of the FEK-M type have a width of the spectral interval transmitted by a light filter of 80100 nm, of the FEK-N-57, FEK-56, FEK-60 types of 3040 nm. When working on spectrophotometers, absorbance is measured over the entire operating range of this device, first after 1020 nm, and after finding the boundaries of maximum absorption, after 1 nm.
As a rule, the description of the standard method of determination, which the laboratory assistant is guided in his work, contains precise instructions regarding the conditions under which the determination of the substance is carried out.
Photometric analysis uses reagents that change color when the pH of the solution changes. Therefore, it is necessary to maintain the pH in an interval as far as possible from the color transition region.
Quantitative photometric analysis is based on the method of calibration curves showing the dependence of the optical density of a solution D on the amount of substance c.
To plot the curve, the optical density of five to eight solutions of the analyte of various concentrations is measured. The plot of optical density versus concentration is used to determine the content of a substance in the analyzed sample.
The absorption coefficient weakly depends on temperature. Therefore, temperature control in photometric measurements is not necessary. A change in temperature within ±5°C practically does not affect the optical density.
The nature of the solvent has a significant effect on the optical density, other things being equal, so the construction of calibration graphs and measurements in the analyzed products must be carried out in the same solvent.
To work in the UV region, water, alcohol, ether, saturated hydrocarbons are used.
Since the optical density depends on the layer thickness, the choice of cuvettes should be made in such a way that the values of optical densities for a series of reference (standard) solutions are in the range of 0.1 - 1.0, which corresponds to the smallest measurement error.
The same is done if the cuvette is not suitable for measuring the optical densities of solutions of the beginning of a series of standard solutions.
The concentration range of the analyte must also be selected in such a way that the measured optical density of the solution falls within the range of 0.1-1.0.
For the analysis of petroleum products, additives to them, photoelectrocolorimeters FEK-M, FEK-56, FEK-N-57, FEK-60, KFO, KFK-2, as well as spectrophotometers SF-4A, SF-26, SF-46 ( see Chapter 1).
In oil refining, it is customary to determine the refractive index n D at an incident light wavelength of 589 nm. The measurement is carried out using a refractometer.
The refractive index depends on temperature. As ce increases, the refractive indices of liquids decrease.
Table 1. Refractive indices of some compounds at different temperatures
Therefore, measurements must be carried out at a constant: temperature (Table 3.1).
During the measurement, the temperature of the prism chamber is maintained constant by passing water from the thermostat through the prism shirts. If the refractive index is measured at a temperature other than 20° C., then a temperature correction is applied to the refractive index value.
When determining the refractive index of dark petroleum products, for which it is difficult to obtain a sharp boundary when using transmitted light, reflected light is used. For this purpose, open a window in the upper prism, turn the mirror over and illuminate the window with bright light.
Sometimes, in this case, the boundary is not clear enough, but it is still possible to make a reading with an accuracy of 0.0010. For best results, work in an after-foam room and use diffused light of varying intensity, which can be limited by the opening of the working prism.
Electrochemical methods
Electrochemical methods of analysis are used either for direct measurements based on the dependence of the analytical signal - composition, or to indicate the end point of the titration in titrimetry.
For laboratory practice, conductometric titration is more commonly used, in which the measurement of electrical conductivity is used to determine the equivalence point during the titration.
Coulometry is an analysis method based on the interaction of solutes with an electric current. The amount of electricity consumed for the electrolysis of the substance in the analytical reaction is measured and the content of the test substance in the sample is calculated.
Potentiometric method
In the practice of oil refining, the most widely used potentiometric method of analysis is based on measuring the potential of an electrode immersed in the analyzed solution. The value of the potential arising on the electrodes depends on the composition of the solution.
An electrode whose potential depends on the activity (concentration) of certain ions in a solution is called an indicator electrode.
To measure the potential of the indicator electrode in the solution, immerse the second electrode, the potential of which does not depend on the concentration of the ions being determined. Such an electrode is called a reference electrode.
Most often, two classes of indicator electrodes are used in potentiometry:
electron-exchange electrodes, on the interphase boundaries of which reactions occur with the participation of electrons;
ion-exchange, or and it is selective electrodes, at the interphase boundaries of which reactions occur associated with the exchange of ions. Such electrodes are also called membrane electrodes.
Ion-selective electrodes are divided into groups: glass, solid with a homogeneous or heterogeneous membrane; liquid (based on ionic associates, complex metal-containing compounds); gas.
Potentiometric analysis is based on the Nernst equation
E \u003d const + (0.059 / n) / lg a,
where n is the charge of the potential-determining ion or the number of electrons participating in the reaction; a is the activity of potential-determining ions.
Let us consider in more detail the main types of electrodes used in potentiometry.
electron exchange electrodes. Inert metals, such as platinum and gold, are often used as indicator electrodes in redox reactions. The potential arising on a platinum electrode depends on the ratio of the concentrations of the oxidized and reduced forms of one or more substances in solution.
Metal indicator electrodes are made from a flat metal plate, twisted wire or metallized glass. Domestic industry produces thin-layer platinum electrode ETPL-01M.
Ion selective electrodes. The most widely used glass electrode is designed to measure pH.
The glass electrode is usually used in tandem with a silver chloride reference electrode.
The domestic industry commercially produces glass electrodes ESL-11G-05, ESL-41G-04, ESL-63-07, ESL-43-07, suitable for measuring pH in the range from 0 to 14.
In addition to glass electrodes for measuring pH, glass electrodes are also produced for measuring the activity of alkali metals, such as Na + ions (ECNa-51-07), K + ions (ESL-91-07).
Before starting work, glass electrodes should be kept for some time in a 0.1 M hydrochloric acid solution.
Under no circumstances should the glass bead be wiped off, as this may destroy the surface of the electrode. It is strictly forbidden to scratch the surface of the glass electrode with sharp objects, as the thickness of the glass ball is tenths of a millimeter, and this will damage the sensitive element.
The rules for working with glass electrodes fully apply to other ion-selective electrodes.
The domestic industry produces silver chloride electrodes of the EVL-1MZ, EVL-1ML types.
The installation scheme for potentiometric measurements with an indicator electrode and a reference electrode is shown in fig. 3.8.
Tsafety and labor protection in the laboratory
When analyzing petroleum products, one has to work with fire, combustible, explosive, toxic and caustic substances. In this regard, violation of safety and labor protection requirements, failure to observe the necessary precautions can lead to poisoning, burns, cuts, etc.
GENERAL PROVISIONS
Work can only be started if all its stages are clear and beyond doubt. If there are any doubts, please contact your supervisor immediately. Before performing unfamiliar operations, each novice laboratory assistant should receive detailed individual instruction.
All work associated with increased danger must be carried out only under the direct supervision of an experienced worker or work supervisor.
Each laboratory assistant must have overalls for individual use - a dressing gown, and in some cases a headgear and a rubberized apron and protective equipment - glasses and rubber gloves.
When performing any work related to the use of pressure, vacuum, or in cases where splashing of a toxic liquid is possible (for example, when diluting acids and dissolving alkalis), laboratory workers must wear safety goggles.
4. Each laboratory worker should know where in the laboratory there is a first aid kit * containing everything necessary for first aid, as well as where fire extinguishers, boxes With sand, asbestos blankets to extinguish large fires.
5. Only the instruments and equipment necessary for this work should be at the workplace. Everything that can interfere with the elimination of the consequences of a possible accident must be removed.
6. In the laboratory it is forbidden: to work with faulty ventilation;
perform work not directly related to the performance of a specific analysis; work without overalls;
7. Work in the laboratory alone;
leave unattended operating installations, non-stationary heating devices, open flames.
HOW TO WORK WITH CHEMICALS.
A significant number of accidents in laboratories are caused by careless or inept handling of various reagents. Poisoning, burns, explosions are an inevitable consequence of violating the rules of work.
Vessels containing poisonous liquids must be tightly stoppered and labeled "Poison" or "Toxic Substance"; under no circumstances should they be left on the desktop.
Special care is required when handling leaded petroleum products. In these cases, be sure to follow the special rules approved by the Chief Sanitary Doctor of the USSR ("Rules for the storage, transportation and use of leaded gasolines in motor vehicles").
It is strictly forbidden to use leaded gasoline as a fuel for burners and blowtorches and a solvent in laboratory work, as well as for washing hands, dishes, etc. is strictly prohibited. Storage of food and its reception in places of work with ethylated oil products is unacceptable.
The overalls of laboratory workers who are directly involved in the analysis of leaded products should be degassed and laundered regularly. In the absence of degassing chambers, overalls must be put in kerosene for at least 2 hours, then squeezed out, boiled in water, then rinsed abundantly with hot water or only then washed.
After working with leaded gasoline, wash your hands immediately with kerosene, and then your face and hands with warm water and soap.
To prevent chemicals from entering the skin, mouth, respiratory tract, the following precautions must be observed:
1. In laboratory workrooms, stocks of reagents, especially volatile ones, should not be created. The reagents necessary for the current work must be kept tightly closed, and the most volatile (for example, hydrochloric acid, ammonia, etc.) should be kept on special shelves in a fume hood.
Spilled or accidentally spilled reagents should be cleaned up immediately and carefully.
Many reagents arrive at the laboratory in large containers. The selection of small portions of substances directly from drums, large bottles, barrels, etc. is prohibited.
Therefore, a fairly frequent operation in laboratory practical work is the packaging of reagents. This operation should be carried out only by experienced workers who are well aware of the properties of these substances.
The packaging of solid reagents that can irritate the skin or mucous membranes should be done with gloves, goggles or a mask. Hair should be removed under a beret or scarf, the cuffs and collar of the gown should fit snugly against the body.
After working with dusty substances, you should take a shower, and put the overalls in the wash. Respirators or gas masks are used to protect the respiratory organs from dust and caustic fumes. You can not replace respirators with gauze bandages - they are not effective enough.
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