Optical density. Photocolorimeters

OPTICAL DENSITY

density D, a measure of the opacity of a layer of matter to light rays. Equal to the decimal logarithm of the ratio of the radiation flux F0 incident on the layer to the flux F attenuated as a result of absorption and scattering passing through this layer: D lg (F0/ F), otherwise, O.p. is the logarithm of the reciprocal of the transmittance coefficient layer of matter: D lg (1/t). (In the definition of the sometimes used natural op., the decimal logarithm lg is replaced by the natural ln.) The concept of op. was introduced by R. Bunsen; it is used to characterize the attenuation of optical radiation (light) in layers and films of various substances (dyes, solutions, colored and milk glasses and much more), in light filters and other optical products. O.P. is used especially widely for the quantitative assessment of developed photographic layers in both black-and-white and color photography, where the methods of its measurement form the content of a separate discipline—densitometry. There are several types of optical radiation depending on the nature of the incident radiation and the method of measuring the transmitted radiation fluxes (Fig.).

The operating frequency depends on the set of frequencies n (wavelengths l) characterizing the original flow; its value for the limiting case of one single n is called monochromatic OP. The regular (Fig. , a) monochromatic OP of a layer of a non-scattering medium (without taking into account corrections for reflection from the front and rear boundaries of the layer) is equal to 0.4343 k n l, where k n is the natural absorption index of the medium, l is the thickness of the layer (k n l k cl is the index in the Bouguer-Lambert-Beer law equation; if scattering in the medium cannot be neglected, k n is replaced by the natural attenuation index). For a mixture of non-reacting substances or a set of media located one after the other, the opacities of this type are additive, that is, equal to the sum of the same opacities of individual substances or individual media, respectively. The same is true for regular nonmonochromatic radiation (radiation of a complex spectral composition) in the case of media with nonselective (independent of n) absorption. Regular non-monochromatic The O.P. of a set of media with selective absorption is less than the sum of the O.P. of these media. (For instruments for measuring O.P., see the articles Densitometer, Microphotometer, Spectrozonal aerial photography, Spectrosensitometer, Spectrophotometer, Photometer.)

Lit.: Gorokhovsky Yu. N., Levenberg T. M., General sensitometry. Theory and practice, M., 1963; James T., Higgins J., Fundamentals of the Theory of the Photographic Process, trans. from English, M., 1954.

L. N. Kaporsky.

Great Soviet Encyclopedia, TSB. 2012

I. Terms and definitions

Standard solution (sr)- this is a solution containing per unit volume a certain amount of the test substance or its chemical analytical equivalent (GOST 12.1.016 - 79).

Test solution (ir) - this is a solution in which it is necessary to determine the content of the test substance or its chemical analytical equivalent (GOST 12.1.016 - 79).

Calibration chart- graphical expression of the dependence of the optical density of the signal on the concentration of the test substance (GOST 12.1.016 - 79).

Maximum permissible concentration (MPC)) harmful substance - this is a concentration that, with daily (except for weekends) work for 8 hours or other working hours, but not more than 40 hours a week throughout the entire working experience, cannot cause diseases or health problems detected by modern research methods, in the process of work or in the long term of the life of the present or subsequent generations (GOST 12.1.016 - 79).

Colorimetry - This is a method for quantitative analysis of the content of an ion in a transparent solution, based on measuring the intensity of its color.

II. Theoretical part

The colorimetric method of analysis is based on the relationship between two quantities: the concentration of the solution and its optical density (degree of coloration).

The color of the solution can be caused either by the presence of the ion itself (MnO 4 -, Cr 2 O 7 2- ), and the formation of a colored compound as a result of the chemical interaction of the ion under study with the reagent.

For example, the weakly colored Fe 3 ion + gives a blood-red compound when reacted with thiocyanate ions SCH -, copper ion Cu 2+ forms a bright blue complex ion 2 + when interacting with an aqueous solution of ammonia.

The color of the solution is due to the selective absorption of light rays of a certain wavelength: the colored solution absorbs those rays whose wavelength corresponds to the complementary color. For example: blue-green and red, blue and yellow are called complementary colors.

Iron thiocyanate solution appears red because it absorbs predominantly green rays (  5000Á) and transmits red ones; on the contrary, a green-colored solution transmits green rays and absorbs red ones.

The colorimetric method of analysis is based on the ability of colored solutions to absorb light in the wavelength range from ultraviolet to infrared. Absorption depends on the properties of the substance and its concentration. With this method of analysis, the substance under study is part of an aqueous solution that absorbs light, and its amount is determined by the light flux passing through the solution. These measurements are carried out using photocolorimeters. The action of these devices is based on changes in the intensity of the light flux when passing through the solution, depending on the thickness of the layer, degree of color and concentration. The measure of concentration is optical density (D). The higher the concentration of a substance in a solution, the greater the optical density of the solution and the lower its light transmittance. The optical density of a colored solution is directly proportional to the concentration of the substance in the solution. It must be measured at the wavelength at which the substance under study has maximum light absorption. This is achieved by selecting light filters and cuvettes for the solution.

The preliminary selection of cuvettes is made visually according to the color intensity of the solution. If the solution is intensely colored (dark), use cuvettes with a short operating wavelength. In the case of weakly colored solutions, cuvettes with a longer wavelength are recommended. A solution is poured into a pre-selected cuvette, its optical density is measured by turning on a light filter in the path of the rays. When measuring a series of solutions, the cuvette is filled with a solution of average concentration. If the obtained optical density value is approximately 0.3-0.5, this cuvette is selected to work with this solution. If the optical density is more than 0.5-0.6, take a cuvette with a shorter working wavelength, if the optical density is less than 0.2-0.3, choose a cuvette with a longer working wavelength.

The accuracy of measurements is greatly influenced by the cleanliness of the working edges of the cuvettes. During work cuvettes are grasped with hands only by the non-working edges, and after filling with solution carefully monitor the absence of even the smallest air bubbles on the walls of the cuvettes.

According to the law Bouguer-Lambert-Baer, the proportion of absorbed light depends on the thickness of the solution layer h, solution concentration C and intensity of incident light I 0

where I - intensity of light passing through the analyzed solution;

I is the intensity of the incident light;

h is the thickness of the solution layer;

C is the concentration of the solution;

The absorption coefficient is a constant value for a given colored compound.

Taking logarithm of this expression, we get:

(2)

where D is the optical density of the solution and is a constant value for each substance.

Optical density D characterizes the ability of a solution to absorb light.

If the solution does not absorb light at all, then D = 0 and I t =I, since expression (2) is equal to zero.

If the solution absorbs the light rays completely, then D equals infinity and I = 0, since expression (2) equals infinity.

If the solution absorbs 90% of the incident light, then D = 1 and

I t =0.1, since expression (2) is equal to one.

For accurate colorimetric calculations, the change in optical density should not exceed the range of 0.1 - 1.

For two solutions of different layer thicknesses and concentrations, but the same optical density, we can write:

D = h 1 C 1 = h 2 C 2,

For two solutions of the same thickness, but different concentrations, we can write:

D 1 = h 1 C 1 and D 2 = h 2 C 2,

As can be seen from expressions (3) and (4), in practice, to determine the concentration of a solution using the colorimetric method, it is necessary to have a standard solution, that is, a solution with known parameters (C, D).

The definition can be done in different ways:

1. You can equalize the optical densities of the test and standard solutions by changing their concentration or the thickness of the solution layer;

2. You can measure the optical density of these solutions and calculate the desired concentration using expression (4).

To implement the first method, special devices are used - colorimeters. They are based on a visual assessment of the intensity of transmitted light and therefore their accuracy is relatively low.

The second method - measuring optical density - is carried out using much more accurate instruments - photocolorimeters and spectrophotometers, and it is this method that is used in this laboratory work.

When working with a photocolorimeter, the technique of constructing a calibration graph is often used: they measure the optical density of several standard solutions and construct a graph in coordinates D = f(C). Then the optical density of the test solution is measured and the desired concentration is determined from the calibration graph.

The equation Bouguer-Lambert-Baer This is true only for monochromatic light, so accurate colorimetric measurements are carried out using light filters - colored plates that transmit light rays in a certain wavelength range. For work, select a light filter that provides maximum optical density of the solution. Light filters installed on a photocolorimeter transmit rays not of a strictly defined wavelength, but in a certain limited range. As a result, the measurement error on the photocolorimeter is no more than ±3 % on the weight of the analyte. Strictly monochromatic light is used in special devices - spectrophotometers, which have higher measurement accuracy.

The accuracy of colorimetric measurements depends on the concentration of the solution, the presence of impurities, temperature, acidity of the solution medium, and determination time. This method can only analyze dilute solutions, that is, those for which the dependence D = f(C)-straight.

When analyzing concentrated solutions, they are first diluted, and when calculating the desired concentration, a correction for dilution is made. However, the measurement accuracy decreases.

Impurities can affect the accuracy of measurements by either producing a colored compound with the added reagent or by hindering the formation of a colored compound of the ion being studied.

The colorimetric analysis method is currently used to carry out analyzes in various fields of science. It allows accurate and rapid measurements using negligible amounts of substance, insufficient for volumetric or gravimetric analysis.

Bodies that transmit and absorb light (except for dull and turbid media) are characterized by optical transparency θ, opacity O and optical density D.

Optical density is often used instead of transmittance and reflectance. D.

In photography, optical density is most common for expressing the spectral properties of filters and a measure of blackening (darkening) of negatives and positives. The density value depends on the following simultaneously acting factors: the structure of the incident light flux (converging, diverging, parallel rays or scattered light) and the structure of the transmitted or reflected flux (integral, regular, diffuse).

Optical density D, a measure of the opacity of a layer of substance to light rays. It is equal to the tenth logarithm of the ratio of the radiation flux F0 incident on the layer to the flux F weakened as a result of absorption and scattering passing through this layer: D = log (F0/F), otherwise, Optical density is the logarithm of the reciprocal of the transmittance coefficient of the layer of matter: D = log (1/t).

In determining optical density, the decimal logarithm lg is sometimes replaced by the natural logarithm ln.

The concept of optical density was introduced by R. Bunsen; it is used to characterize the attenuation of optical radiation (light) in layers and films of various substances (dyes, solutions, colored and milky glasses, etc.), in light filters and other optical products.

Optical density is especially widely used for quantitative assessment of developed photographic layers in both black and white and color photography, where methods for measuring it form the content of a separate discipline - densitometry. There are several types of optical density depending on the nature of the incident radiation and the method of measuring the transmitted radiation fluxes

Density varies D for white light, monochromatic Dλ for individual wavelengths and zonal D zones, expressing weakening of the light flux in the blue, green or red zone of the spectrum (D c 3, D 3 3 , D K 3).

Density of transparent media(filters, negatives) is determined in transmitted light by the tenth logarithm of the reciprocal of the transmittance τ:

D τ = log(1/τ) = -logτ

Surface Density is expressed by the magnitude of the reflected light and is determined by the decimal logarithm of the reflection coefficient ρ:

D ρ = log(1/ ρ ) = - logρ .

The density value D = l weakens light by 10 times.

The range of optical densities of transparent media is practically unlimited: from complete light transmission (D= 0) until it is completely absorbed (D = 6 or more, weakening by millions of times). The range of densities of the surfaces of objects is limited by the content of the surface reflected component in their reflected light of the order of 4-1% (black printing ink, black cloth). Almost limiting densities D= 2.1...2.4 have black velvet and black fur, limited by the surface reflected component of the order of 0.6-0.3%.

Optical density is connected by simple relationships with the concentration of the light-absorbing substance and with the visual perception of the observed object - its lightness, which explains the widespread use of this parameter.

Replacing the optical coefficients with the radiation fluxes - incident on the medium (Ф 0) and emerging from it (Фτ or Фρ), we obtain the expressions

The more light is absorbed by a medium, the darker it is and the higher its optical density in both transmitted and reflected light.

Optical density can be determined from light coefficients. In this case it is called visual.

Visual Density in transmitted light is equal to the logarithm of the reciprocal of the light transmittance:

Visual density in reflected light is determined by the formula

For neutral gray optical media. those. for gray filters, gray scales, black and white images, the optical and light coefficients are the same, therefore the optical densities are the same:

If it is known what density we are talking about, the index at D lowered. Described above optical densities – integral, they reflect changes in the power characteristics of white (mixed) radiation. If the optical density is measured for monochromatic radiation, then it is called monochromatic(spectral). It is determined using monochromatic radiation fluxes Fλ according to the formula

In the above formulas, radiant fluxes Ф can be replaced by luminous fluxes F λ, which follows from the expression

Therefore we can write:

For colored media, the integrated optical and visual densities do not coincide, since they are calculated using different formulas:

For photographic materials with a transparent substrate, the optical density is determined without the density of the substrate and the unexposed emulsion layer after processing, collectively called “zero” density or veil density D 0.

The total optical density of two or more light-absorbing layers (for example, light filters) is equal to the sum of the optical densities of each layer (filter). Graphically, the absorption characteristic is expressed by the optical density dependence curve D on the wavelength of white light λ, nm.

Optical transparency Θ – characteristic of a substance 1 cm thick, showing what fraction of the radiation of a given spectrum in the form of parallel rays passes through it without changing direction: Θ = Ф τ / Ф .

Optical transparency is not related to the transmission of radiation in general, but to its directed transmission, and characterizes absorption and scattering at the same time. For example, frosted glass, which is optically opaque, allows diffused light to pass through; UV filters are transparent to visible light and opaque to UV radiation; Black IR filters transmit IR radiation and do not transmit visible light.

Optical transparency is determined by the spectral transmission curve for wavelengths in the optical range of radiation. The transparency of lenses for white light increases when anti-reflective coatings are applied to the lenses. The transparency of the atmosphere depends on the presence in it of small particles of dust, gas, and water vapor that are suspended and affect the nature of the lighting and the image pattern when shooting. The transparency of water depends on various suspensions, turbidity and the thickness of its layer.

Optical opacity O– the ratio of the incident light flux to that transmitted through the layer – the reciprocal of transparency: O = F/F τ= l/Θ. Opacity can vary from unity (total transmission) to infinity and shows how many times the light decreases when passing through the layer. Opacity characterizes the density of the medium. The transition to optical density is expressed by the decimal logarithm of opacity:
D= log O = log (l/τ) = - log τ .

Spectral differences between bodies. According to the nature of emission and absorption of the light flux, all bodies differ from BL and are conventionally divided into selective and gray, distinguished by selective and non-selective absorption, reflection and transmission. Selective bodies include chromatic bodies that have some color, while gray bodies include achromatic ones. The term “gray” is characterized by two characteristics: the nature of emission and absorption relative to the BL and the color of the surface observed in everyday life. The second feature is widely used in visually determining the color of achromatic bodies - white, gray and black, reflecting the spectrum of white light from one to zero, respectively.

The gray body has a degree of light absorption close to that of the black body. The absorption coefficient of a black body is 1, and that of a gray body is close to 1 and also does not depend on the wavelength of radiation or absorption. The distribution of energy emitted across the spectrum for gray bodies for each given temperature is similar to the distribution of energy of a black body at the same temperature, but the radiation intensity is several times lower (Fig. 23).

For non-gray bodies, absorption is selective and depends on wavelength, so they are considered gray only in certain, narrow wavelength intervals for which the absorption coefficient is approximately constant. In the visible region of the spectrum, coal has the properties of a gray body (α = 0.8)< сажа (α = 0,95) и платиновая чернь (α = 0,99).

Selective (selective) bodies have color and are characterized by curves of reflection, transmission or absorption coefficients depending on the wavelength of incident radiation. When illuminated with white light, the color of the surface of such bodies is determined by the maximum values of the spectral reflection curve or the minimum value of the spectral absorption curve. The color of transparent bodies (light filters) is determined mainly by the absorption curve (density D) or transmission curve τ. Spectral absorption and transmission curves characterize the substance of selective bodies only for white light. When they are illuminated with colored light, the spectral reflectance or transmittance curves change.

White, gray and black body colors are a visual sense of achromaticity, applicable to the reflection of surfaces and the transmission of transparent media. Achromaticity is graphically expressed by a horizontal straight line or a barely noticeable wavy line parallel to the abscissa axis and located at different levels of the ordinate axis in the light wavelength range (Fig. 24, a B C). The sensation of white color is created by surfaces with the highest uniformity coefficient

reflections across the spectrum (ρ = 0.9...0.7 - white papers). Gray surfaces have a uniform reflection coefficient p = 0.5...0.05. Black surfaces have ρ = 0.05...0.005 (black cloth, velvet, fur). This distinction is approximate and conditional. For transparent media (for example, neutral gray filters), the achromaticity characteristic is also expressed by a horizontal absorption line (density D, showing to what extent white light is attenuated).

Surface lightness- this is the relative degree of visual sensation resulting from the action of the color of reflected radiation on the three color-sensing centers of vision. Graphically, lightness is expressed by the total density of this radiation in the white light range. In general lighting engineering, lightness is incorrectly used to visually quantify the difference between two adjacent surfaces that differ in brightness.

Lightness of a white surface illuminated by white light . The lightness of a perfectly white surface (coated with barium or magnesium sulfate) with ρ = 0.99 is taken as 100%. At the same time, the area characterizing its area on the graph (Fig. 24, A) limited by the lightness line at ρ = 1 or 100%. In practice, surfaces whose lightness corresponds to 80-90% (ρ = 0.8...0.9) are considered white. The lightness line of gray surfaces approaches the x-axis (Fig. 24, e), since they reflect part of the white light. The line of lightness of black velvet, which practically does not reflect light, is aligned with the x-axis.

Lightness of colored surfaces illuminated with white light , determined on the graph by the area limited by the spectral reflectance curve. Since the shapeless area cannot reflect the quantitative degree of lightness, it is converted into the area of a rectangle with the base on the x-axis (Fig. 24, Where). The height of the rectangle determines the lightness percentage .

Lightness of colored surfaces illuminated by colored light, expressed on a graph by the area limited by the resulting curve obtained by multiplying the spectral characteristic of illumination by the spectral characteristic of reflection of the surface. If the color of the light does not match the color of the surface, then the reflected light changes its hue, saturation and lightness.

COLORED SOLUTIONS USING CONCENTRATOR

PHOTOELECTRIC CALORIMETER KFK–2

Goal of the work: study the phenomenon of attenuation of light when passing through a substance and the photometric characteristics of the substance, study the device of the concentration photoelectric calorimeter KFK-2 and the method of working with it, determine the optical density and concentration of a colored solution using KFK-2.

Devices and accessories: photoelectric concentration calorimeter KFK - 2, test solution, set of solutions of standard concentration.

Theory of operation

When light falls on the interface between two media, the light is partially reflected and partially penetrates from the first substance to the second. Light electromagnetic waves set into oscillatory motion both free electrons of the substance and bound electrons located on the outer shells of atoms (optical electrons), which emit secondary waves with the frequency of the incident electromagnetic wave. Secondary waves form a reflected wave and a wave penetrating into the substance.

In substances with a high density of free electrons (metals), secondary waves generate a strong reflected wave, the intensity of which can reach 95% of the intensity of the incident wave. The same part of the light energy that penetrates into the metal experiences strong absorption in it, and the energy of the light wave is converted into heat. Therefore, metals strongly reflect the light falling on them and are practically opaque.

In semiconductors, the density of free electrons is lower than in metals, and they absorb visible light less well, and in the infrared region they are generally transparent. Dielectrics absorb light selectively and are transparent only for certain parts of the spectrum.

In general, when light falls on a substance, the incident luminous flux F 0 can be represented as the sum of light fluxes:

Where Ф r– reflected, F a- absorbed, Ф t– light flux passing through a substance.

The phenomenon of interaction of light with matter is described by dimensionless quantities called reflection, absorption and transmission coefficients. For the same substance

r+a +t = 1. (2)

For opaque bodies t= 0; for perfectly white bodies r = 1; for absolute black bodies a = 1.

Magnitude is called the optical density of the substance.

Odds r, a, t characterize the photometric properties of a substance and are determined by photometric methods.

Photometric methods of analysis are widely used in veterinary medicine, animal science, soil science, and materials technology. When studying substances dissolved in a practically non-absorbing solvent, photometric methods are based on measuring the absorption of light and on the relationship between absorption and concentration of solutions. Instruments designed for absorption (absorption - absorption) analysis of transparent media are called spectrophotometers and photocalorimeters. In them, using photocells, the colors of the solutions under study are compared with the standard.

The relationship between the absorption of light by a colored solution and the concentration of the substance obeys the combined Bouguer–Lambert–Beer law:

, (3)

Where I 0 – intensity of the light flux incident on the solution; I- intensity of the light flux passing through the solution; c- concentration of the colored substance in the solution; l- thickness of the absorbing layer in the solution; k- absorption coefficient, which depends on the nature of the solute, solvent, temperature and wavelength of light.

If With expressed in mol/l, and l- in centimeters, then k becomes the molar absorption coefficient and is denoted e l, therefore:

. (4)

Taking logarithms of (4), we get:

The left side of expression (5) is the optical density of the solution. Taking into account the concept of optical density, the Bouguer–Lambert–Beer law will take the form:

that is, the optical density of a solution under certain conditions is directly proportional to the concentration of the colored substance in the solution and the thickness of the absorbing layer.

In practice, cases of deviation from the combined absorption law are observed. This occurs because some colored compounds in the solution undergo changes due to the processes of dissociation, solvation, hydrolysis, polymerization, and interaction with other components of the solution.

Dependency graph type D = f(c) shown in Fig. 1.

Colored compounds have selective absorption of light, i.e. The optical density of the colored solution is different for different wavelengths of incident light. Measurement of optical density in order to determine the concentration of the solution is carried out in the region of maximum absorption, i.e. at the wavelength

incident light close to l max.

To photometrically determine the concentration of a solution, first construct a calibration graph D = f(c). To do this, prepare a series of standard solutions. Then the values of their optical density are measured and a dependence graph is plotted

D = f(c). To build it you need to have 5 – 8 points.

Having experimentally determined the optical density of the solution under study, find its value on the ordinate axis of the calibration graph D = f(c), and then the corresponding concentration value is counted on the x-axis With X.

The photoelectric concentration calorimeter KFK-2 used in this work is designed to measure the ratio of light fluxes in individual sections of wavelengths in the range of 315 - 980 nm, emitted by light filters, and allows you to determine the transmittance and optical density of liquid solutions and solids, as well as the concentration of substances in solutions method of constructing calibration graphs D = f(c).

The principle of measuring the optical characteristics of substances with the KFK-2 photocalorimeter is that light fluxes are sent alternately to the photodetector (photocell) - full I 0 and passed through the medium under study I and the ratio of these flows is determined.

The appearance of the KFK-2 photocalorimeter is shown in Fig. 2. It includes

includes a light source, an optical part, a set of light filters, photodetectors and a recording device, the scale of which is calibrated for light transmittance and optical density readings. On the front panel of the KFK-2 photocalorimeter there are:

1 - microammeter with a scale digitized in the values of the coefficient of pro-

launches T and optical density D;

2 - illuminator;

3 - knob for switching light filters;

4 - switch of cuvettes in the light beam;

5 - photodetector switch “Sensitivity”;

6 - knobs “Setting 100”: “Coarse” and “Fine”;

7 - cuvette compartment.

Work order

1. Connect the device to the network. Warm up for 10 – 15 minutes.

2. With the cuvette compartment open, set the microammeter needle to “0”

on the "T" scale.

3. Set the minimum sensitivity; to do this, turn the “Sensitivity” knob

Move the “Setup 100” “Coarse” knob to the extreme left position.

4. Place a cuvette with a solvent or control solution into the light beam.

rum in relation to which the measurement is made.

5. Close the lid of the cuvette compartment.

6. Use the “Sensitivity” and “Setting 100” knobs to set “Coarse” and “Fine”

reading 100 on the photocalorimeter scale. The “Sensitivity” knob can be in one of three positions “1”, “2”, or “3”.

7. By turning knob “4”, replace the cuvette with the solvent with the cuvette with the test substance

solution.

8. Take a reading on the microammeter scale corresponding to the pro-

release of the test solution as a percentage, on the “T” scale or on the “D” scale - in units of optical density.

9. Carry out measurements 3–5 times and the final value of the measured value is

divide as the arithmetic mean of the obtained values.

10. Determine the absolute measurement error of the desired quantity.

Task No. 1. Study of the dependence of optical density on length

Waves of incident light

1.1. For a standard solution, determine the optical density at different frequencies of incident light.

1.2. Enter the data into table 1.

1.3. Plot the dependence of optical density on wavelength l pa-

giving light D = f(l).

1.4. Define l and filter number for D max .

Table 1

Task No. 2. Checking the dependence of optical density on thickness

Absorbent layer

2.1. For a standard solution, using a filter with l D for cuvettes of various sizes.

2.2. Enter the data into table 2.

table 2

2.3. Build a dependency graph D = f(l).

Task No. 3. Construction of a calibration graph and determination of concentrations

Walkie-talkie of unknown solution

3.1. For a series of standard solutions of known concentration, using light

tofilter with l max (see task No. 1), determine D.

3.2. Enter the measurement data in table 3.

Table 3

3.3. Build a calibration graph D = f(c).

3.4. On schedule D = f(c) Determine the concentration of an unknown solution.

Control questions

1. The phenomenon of attenuation of light when passing through matter, the absorption mechanism

tions for different types of matter.

2. Parameters characterizing the photometric properties of a substance.

3. Explain the essence of photometric methods of analysis.

4. Formulate the combined Bouguer–Lambert–Beer absorption law.

5. What are the reasons for possible deviations of the properties of solutions from the combined

takeover horse?

6. Molar absorption coefficient, its definition and factors on which it depends

7. How to select the wavelength of absorbed radiation during photocaloric

rimetric measurements?

1. How is a calibration graph constructed?

2. Explain the design and operating principle of the KFK-2 photocalorimeter.

3. Where and for what is absorption analysis used?

Literature

1. Trofimova T. I. Physics course. M.: Higher. school, 1994. Part 5, ch. 24, § 187.

2. Savelyev I.V. Course of general physics. M.: Nauka, 1977. Volume 2, part 3, chapter. XX,

3. Grabovsky R.I. Physics course. St. Petersburg: Lan. 2002. Part P, ch. VI, § 50.

LABORATORY WORK No. 4–03

Optical density. Photocolorimeters

See also interpretations, synonyms, meanings of the word and what OPTICAL DENSITY is in Russian in dictionaries, encyclopedias and reference books:

I. Terms and definitions

II. Theoretical part