Chemistry of color qualitative reactions. Colored rain White curd sediment formula
The Pambak River in the Lori region in northern Armenia has acquired a reddish hue, water samples have been taken for examination.
April 1999 after the NATO bombing of Yugoslavia and the destruction of petrochemical enterprises, a poisonous "black rain" passed over the town of Pancevo, containing a huge amount of heavy metals and organic compounds harmful to human life. Soil and groundwater were seriously polluted, which turned out to be contaminated with ethylene and chlorine. A huge amount of oil, oil products, ammonia and amino acids got into the Danube.
June-July 2000 in some regions of Dagestan and North Ossetia, in particular, in the city of Vladikavkaz, there were "colored rains". As a result of analyzes of water samples, an increased content of chemical elements was found. They exceeded the maximum allowable concentrations of cobalt (more than four times) and zinc (more than 434 times). Laboratory studies confirmed that the composition of the polluted rain was identical to the chemical composition of the samples taken on the territory of JSC "Electrozinc", which violated the standards for maximum allowable emissions into the atmosphere, approved by the Ministry of Environmental Protection.
In 2000 and 2002"rusty" precipitation fell in the Altai Territory and the Altai Republic. The weather anomaly was caused by strong emissions of combustion products at the Ust-Kamenogorsk metallurgical plant.
July-September 2001"red rains" repeatedly fell out in the Indian state of Kerala. Several hypotheses of the origin of red particles were put forward at once: someone considered them to be red dust carried by the wind from the Arabian Desert, someone recognized them as fungal spores or ocean algae. A version of their extraterrestrial origin was put forward. According to scientists, a total of about 50 tons of this strange substance fell on the ground along with precipitation.
In October 2001 residents of the southwestern regions of Sweden fell under abnormal rain. After the rain, gray-yellow stains remained on the surface of the earth. Swedish experts, and in particular a researcher from the Gothenburg Geoscience Center Lars Fransen, said that strong winds "dragged" red sandy dust from the Sahara, raised it to a height of up to 5 thousand meters and then poured it along with the rain in Sweden.
Summer 2002 green rain poured over the Indian village of Sangranpur near the city of Kolkata. Local authorities announced that there was no chemical attack. The examination of scientists who arrived at the site determined that the green cloud is nothing more than pollen from flowers and mangoes contained in bee excrement, and does not pose a danger to humans.
In 2003 in Dagestan, precipitation in the form of salt deposits fell. Cars standing in the open air were covered with a layer of salt. According to meteorologists, the reason for this was a cyclone that came from the regions of Turkey and Iran. Fine particles of sand and dust raised by a strong wind from the developed quarries in the territory of Dagestan mixed with water dust raised from the surface of the Caspian Sea. The mixture was concentrated in clouds that moved to the coastal regions of Dagestan, where unusual rain fell.
Winter 2004 orange-colored snow fell in eastern Poland. At the same time, residents of Transcarpathia observed him in the villages of Quiet and Gusinoe. According to one version, sandstorms in Saudi Arabia became the reason for the orange color of the snow: grains of sand, picked up by a strong wind, accumulated in the upper atmosphere and fell along with snow in Transcarpathia.
April 19, 2005 red rain fell in Kantemirovskiy and Kalacheevskiy districts of the Voronezh region. Precipitation left an unusual trace on the roofs of houses, fields, agricultural machinery. In a soil sample, traces of ocher, a natural pigment for paint production, were found. It contained hydroxides of iron and clay. Further investigation showed that there had been a release at the ocher factory in the village of Zhuravka, which led to the color of rain clouds in red. According to experts, the precipitation did not pose a danger to the health of people and animals.
April 19, 2005 over several regions of the Stavropol Territory, the sky acquired a yellowish tint, and then it began to rain, the drops of which were colorless. After drying, the drops were left on cars and on dark beige clothes, which were not washed off afterwards. The same rain fell on April 22 in Orel. The analyzes carried out showed that the sediments contained alkali, namely, nitrogenous compounds. The precipitation was very concentrated.
April 2005 for several days, orange rains were falling in Ukraine - in the Nikolaev region and in the Crimea. Colored precipitation also covered Donetsk, Dnepropetrovsk, Zaporozhye, Kherson regions these days. Ukrainian weather forecasters said that the orange color of the rain acquired due to a dust hurricane. The wind brought dust particles from North Africa.
February 2006 gray-yellow snow fell on the territory of the village of Sabo, located 80 km south of the city of Okha in the north of Sakhalin. According to eyewitnesses, oily spots of a gray-yellow color and with an unusual strange smell formed on the surface of the water obtained by melting suspicious snow. Experts believe that unusual precipitation could be the consequences of the activity of one of the Far Eastern volcanoes. Possibly, the pollution of the environment by products of the oil and gas industry is to blame. The reason for the yellowing of the snow was not exactly established.
February 24-26, 2006 in some areas of Colorado (USA) it was brown snow, almost like chocolate in color. "Chocolate" snow in Colorado - a consequence of a long drought in neighboring Arizona: there are giant clouds of dust that mixes with snow. Sometimes volcanic eruptions give the same result.
March 2006 creamy-pink snow fell in the north of Primorsky Krai. Experts explained the unusual phenomenon by the fact that the cyclone had previously passed through the territory of Mongolia, where strong dust storms raged at that time, covering large expanses of desert territories. Dust particles were drawn into the vortex of the cyclone and colored the precipitation.
March 13, 2006 in South Korea, including Seoul, yellow snow fell. The snow was yellow because it contained yellow sand brought from the deserts of China. The country's meteorological service has warned that snow containing fine sand can be dangerous for the respiratory system.
November 7, 2006 in Krasnoyarsk, light snow fell with green rain. He walked for about half an hour and, having melted, turned into a thin layer of greenish clay. People exposed to green rain experienced tearing and headaches.
January 31, 2007 in the Omsk region, on an area of about 1.5 thousand square kilometers, yellow-orange snow fell with a pungent odor, covered with oily spots. Having passed through the entire Irtysh region, a plume of yellow-orange precipitation touched the Tomsk region along the edge. But the main part of the "acidic" snow fell in the Tarsky, Kolosovsky, Znamensky, Sedelnikovsky and Tyukalinsky districts of the Omsk region. In the colored snow, the iron content was exceeded (according to preliminary laboratory data, the concentration of iron in the snow was 1.2 mg per cubic centimeter, while the maximum allowable rate was 0.3 mg). According to Rospotrebnadzor, such a concentration of iron is not dangerous for human life and health. Abnormal precipitation was studied by laboratories in Omsk, Tomsk and Novosibirsk. At first it was assumed that the snow contained the poisonous substance heptyl, which is a component of rocket fuel. The second version of the appearance of yellow precipitation was the emissions of the metallurgical enterprises of the Urals. However, Tomsk and Novosibirsk experts came to the same conclusion as Omsk - the unusual color of the snow is due to the presence of clay-sand dust, which could get into the Omsk region from Kazakhstan. No toxic substances were found in the snow.
March 2008 yellow snow fell in the Arkhangelsk region. Experts suggested that the yellow color of the snow is due to natural factors. This is due to the high content of sand that got into the clouds as a result of dust storms and tornadoes that occurred elsewhere on the planet.
Lesson objectives:
- determination of the factors that cause the coloring of chemicals;
- expansion and systematization of knowledge on the chemical foundations of the theory of the origin of color;
- development of cognitive interest in the study of qualitative reactions.
Formed competencies of students:
- the ability to analyze the phenomena of the surrounding world in chemical terms;
- the ability to explain chemical phenomena associated with the appearance of color solutions;
- willingness to work independently with information;
- willingness to interact with colleagues and speak in front of an audience.
"All living things strive for color." W. Goethe
Knowledge update
In previous lessons, we have studied the properties of inorganic and organic substances, often using qualitative reactions that indicate the presence of a particular substance by color, smell, or sediment. The crossword puzzle offered to you consists of the names of chemical elements that have color differences.
Crossword solution:
Vertically:
1) Substance that turns flames purple (potassium).
2) The lightest silvery metal (lithium).
Horizontally:
3) The name of this element is "green branch" (thallium)
4) The metal that stains glass blue (niobium)
5) The name of the metal means sky blue (cesium)
6) Violet vapors of this substance were first obtained by Courtois thanks to his cat (iodine).
Motivation of educational activity.
Please note that the solution to the crossword puzzle was related to the color of the substances. But not only chemicals, but the world around us is colorful.
"All living things strive for color." These words of the great genius of poetry truly reflect the peculiarity of the emotions that this or that color evokes in us. We perceive it associatively, i.e. recall something familiar and familiar. The perception of color is accompanied by certain emotions. (Demonstration of paintings by artists).
Students answer questions about emotions on the perception of color.
- The blue color evokes calmness, it is pleasant, it increases the assessment of self-affirmation.
- Green - the color of green plants, the mood of peace, tranquility.
- Yellow is the spirit of happiness, fun, associated with the sun.
- Red is the color of activity, action, you want to achieve results.
- Black - causes sadness, irritation.
Why is the world around us so colorful?
Today we are trying to find the answer to the question "What is a color?" in terms of chemistry.
The topic of the lesson is "Color Chemistry of Qualitative Reactions".
Determination of color factors
It is impossible to consider the chemical essence of color without knowledge of the physical properties of visible light. Without light there is no coloring of objects, everything seems dark. Light is electromagnetic waves. How much joy a rainbow in the sky brings to both children and adults, however, it appears only if the sun's rays are reflected in water droplets and return to the human eye with a multi-colored spectrum. We owe the great English physicist Isaac Newton the fact that he explained this phenomenon: white is a combination of rays of different colors. Each wavelength corresponds to a certain energy that these waves carry. The color of any substance is determined by the wavelength, the energy of which prevails in this radiation. The color of the sky depends on how much sunlight reaches our eyes. Rays with a short wavelength (blue) are reflected from the molecules of air gases and scattered. Our eye perceives them and determines the color of the sky - blue, blue (Table 1.)
Table 1 - Color of substances having one absorption band in the visible part of the spectrum.
The same happens in the case of colored substances. If a substance reflects rays of a certain wavelength, then it is colored. If the energy of light waves of the entire spectrum is equally absorbed or reflected, then the substance appears black or white. From biology lessons, you know that the human eye contains an optical system: the lens and the vitreous body. The retina contains light-sensitive elements: cones and rods. The cones allow us to distinguish colors.
Thus, what we call color is the result of two physical and chemical phenomena: the interaction of light with the molecules of a substance and the effect of waves coming from a substance on the retina of the eyes.
1 color formation factor is light.
Consider examples of the next factor - the structure of substances.
Metals have a crystalline structure, they have an ordered structure of atoms and electrons. Color is related to the mobility of electrons. When illuminating metals, reflection predominates, their color depends on the wavelength they reflect. (Demonstration of the collection of metals). The white luster is due to the uniform reflection of almost the entire set of visible rays. This is the color of aluminum, zinc. Gold has a reddish-yellow color because it absorbs blue, indigo and violet rays. Copper also has a reddish color. Magnesium powder is black, which means that this substance absorbs the entire spectrum of rays.
Let's see how the color of a substance changes from the state of the structure using sulfur as an example.
Demonstration of the video film "Chemical elements".
We conclude: sulfur in the crystalline state is yellow, and in the amorphous state it is black, i.e. in this case, the color factor is the structure of the substance.
What happens to the color of substances when the structure is destroyed, for example, during the dissociation of salt molecules, if these solutions are colored.
CuS0 4 (blue) Cu 2+ + SO 4 2-
NiS0 4 (green) Ni 2+ + SO 4 2-
CuCI 2 (blue) Cu 2+ + 2CI -
FeCI 3 (yellow) Fe 3+ +3CI -
In these solutions, the same anions, different cations give color.
The following solutions have the same cation, but different anions, so the anions are responsible for the color:
K 2 Cr 2 O 7 (orange) 2K + +Cz 2 O 4 2-
K 2 Cr0 4 (yellow) 2K + + Cz0 4 2-
KMnO 4 (violet) K + + Mn04 -
The 3rd factor in the appearance of color is the ionic state of substances.
The color also depends on the environment around the colored particles. Cations and anions in solution are surrounded by a shell of a solvent that affects the ions.
We carry out the following experiment. There is a solution of beet juice (crimson color). Add the following to this solution:
- an experience. Beet juice solution and acetic acid
- an experience. Beet juice solution and NH 4 0H solution
- an experience. A solution of beet juice and water.
In experiment 1, an acidic medium causes a color change to purple, in experiment 2, an alkaline medium changes the color of the beets to blue, and the addition of water (neutral medium) does not cause color changes.
A well-known indicator for the determination of an alkaline environment is phenolphthalein, which changes the color of alkali solutions to crimson.
Experience is being made:
NaOH + phenolphthalein -> crimson color
We conclude: the 4th color change factor is the environment.
Let us consider the case of the environment of an atom of one element by various complexes.
An experiment is being carried out: a qualitative reaction to the Fe 3+ ion:
FeCl 3 + KCNS -> red color
FeCl 3 + K 4 (Fe(CN) 6) -> p-p dark blue
A historical fact is associated with a change in the color of the iron ion when surrounded by potassium thiocyanate in a bloody color.
Student messages.
In 1720, political opponents of Peter I from the clergy organized a "miracle" in one of the St. Petersburg cathedrals - the icon of the Mother of God began to shed tears, which was commented on as a sign of her disapproval of Peter's reforms. Peter I carefully examined the icon and noticed something suspicious: he found small holes in the eyes of the icon. He also found the source of the tears: it was a sponge soaked in a solution of iron thiocyanate, which has a blood-red color. The weight evenly pressed on the sponge, squeezing out drops through a hole in the icon. "Here is the source of miraculous tears," said the emperor.
We are experimenting.
We write words on paper with solutions of CuS0 4 (blue) and FeСI 3 (yellow), then we process the sheet with yellow blood salt K 4 (Fe (CN) 6). The word CuSO 4 (cyan) turns red and the word FeCI 3 (yellow) turns blue-green. There is no change in the oxidation state of the metal, only the environment changed:
2CuS0 4 + K 4 (Fe(CN) 6) Cu 2 (Fe(CN) 6) + 2K 2 SO 4
4FeCl 3 + 3 K 4 (Fe(CN) 6) Fe 4 (Fe(CN) 6) 3 +12 KCI
5th color factor - environment of ions by complexes.
Conclusion.
We have identified the main factors influencing the manifestation of the color of substances.
We realized that color is the result of the absorption of a certain part of the visible spectrum of sunlight by a substance.
A qualitative reaction is a special reaction that detects ions or molecules by color.
Messages of students on the topic "Color serves people".
Animal blood and leaf greens contain similar structures, but blood contains iron ions - Fe, and plants - Mg. This ensures the color: red and green. By the way, the saying "blue blood" is true for deep-sea animals, whose blood contains vanadium instead of iron. Also, algae that grow in places where there is little oxygen have a blue color.
Plants with chlorophyll are able to form organomagnesium substances and use the energy of light. The color of photosynthetic plants is green.
Iron-containing hemoglobin is used to carry oxygen throughout the body. Hemoglobin with oxygen stains the blood bright red, and without oxygen gives the blood a dark color.
Paints and dyes are used by artists, decorators and textile workers. Harmony of color is an integral part of the art of "design". The most ancient paints were charcoal, chalk, clay, cinnabar and some salts such as copper acetate (verdigris).
Phosphor paints are used for road signs and advertisements, rescue boats.
For the purpose of bleaching, substances are introduced into the composition of washing powders that give the fabric a bluish fluorescence.
The surface of all metal objects under the influence of the environment is destroyed. Their protection is most effective with colored pigments: aluminum powder, zinc dust, red lead, chromium oxide.
Reflection.
1. What factors cause the color of chemicals?
2. What substances can be determined by qualitative reactions by color change?
3. What factors determine the color of potassium and copper salts?
Nature, of which chemicals are a part, surrounds us with mysteries, and trying to solve them is one of life's greatest joys.
Today we tried to approach the truth "Chemistry of color" from one side, and maybe you will discover another. The most important thing is that the world of color is cognizable.
Man is born
To create, dare - and nothing else,
To leave a good mark in life
And solve all the difficult problems.
For what? Look for your answer!
Homework.
Give examples of qualitative reactions to iron ions by color change.
Let's imagine the following situation:
You work in a lab and decide to do an experiment. To do this, you opened the cabinet with reagents and suddenly saw the following picture on one of the shelves. Two jars of reagents had their labels peeled off, which were safely left lying nearby. At the same time, it is no longer possible to determine exactly which jar corresponds to which label, and the external signs of the substances by which they could be distinguished are the same.
In this case, the problem can be solved using the so-called qualitative reactions.
Qualitative reactions called such reactions that allow you to distinguish one substance from another, as well as to find out the qualitative composition of unknown substances.
For example, it is known that the cations of some metals, when their salts are added to the burner flame, color it in a certain color:
This method can only work if the substances to be distinguished change the color of the flame in different ways, or one of them does not change color at all.
But, let's say, as luck would have it, the substances you determine do not color the color of the flame, or color it in the same color.
In these cases, it will be necessary to distinguish substances using other reagents.
In what case can we distinguish one substance from another with the help of any reagent?
There are two options:
- One substance reacts with the added reagent, while the other does not. At the same time, it must be clearly seen that the reaction of one of the starting substances with the added reagent has really passed, that is, some external sign of it is observed - a precipitate has formed, a gas has been released, a color change has occurred, etc.
For example, it is impossible to distinguish water from a sodium hydroxide solution using hydrochloric acid, despite the fact that alkalis react perfectly with acids:
NaOH + HCl \u003d NaCl + H 2 O
This is due to the absence of any external signs of a reaction. A transparent colorless solution of hydrochloric acid, when mixed with a colorless hydroxide solution, forms the same transparent solution:
But on the other hand, water can be distinguished from an aqueous solution of alkali, for example, using a solution of magnesium chloride - a white precipitate forms in this reaction:
2NaOH + MgCl 2 = Mg(OH) 2 ↓+ 2NaCl
2) Substances can also be distinguished from each other if they both react with the added reagent, but do so in different ways.
For example, a solution of sodium carbonate can be distinguished from a solution of silver nitrate using a solution of hydrochloric acid.
hydrochloric acid reacts with sodium carbonate to release a colorless, odorless gas - carbon dioxide (CO 2):
2HCl + Na 2 CO 3 \u003d 2NaCl + H 2 O + CO 2
and with silver nitrate to form a white cheesy precipitate AgCl
HCl + AgNO 3 \u003d HNO 3 + AgCl ↓
The tables below show different options for detecting specific ions:
Qualitative reactions to cations
| Cation | Reagent | Sign of reaction |
| Ba 2+ | SO 4 2- | Ba 2+ + SO 4 2- \u003d BaSO 4 ↓ |
| Cu2+ | 1) Precipitation of blue color: Cu 2+ + 2OH - \u003d Cu (OH) 2 ↓ 2) Precipitation of black color: Cu 2+ + S 2- \u003d CuS ↓ |
|
| Pb 2+ | S2- | Precipitation of black color: Pb 2+ + S 2- = PbS↓ |
| Ag+ | Cl- | Precipitation of a white precipitate, insoluble in HNO 3, but soluble in ammonia NH 3 H 2 O: Ag + + Cl − → AgCl↓ |
| Fe2+ | 2) Potassium hexacyanoferrate (III) (red blood salt) K 3 | 1) Precipitation of a white precipitate that turns green in air: Fe 2+ + 2OH - \u003d Fe (OH) 2 ↓ 2) Precipitation of a blue precipitate (turnbull blue): K + + Fe 2+ + 3- = KFe↓ |
| Fe3+ | 2) Potassium hexacyanoferrate (II) (yellow blood salt) K 4 3) Rhodanide ion SCN − | 1) Precipitation of brown color: Fe 3+ + 3OH - \u003d Fe (OH) 3 ↓ 2) Precipitation of a blue precipitate (Prussian blue): K + + Fe 3+ + 4- = KFe↓ 3) The appearance of intense red (blood red) staining: Fe 3+ + 3SCN - = Fe(SCN) 3 |
| Al 3+ | Alkali (hydroxide amphoteric properties) | Precipitation of a white precipitate of aluminum hydroxide when a small amount of alkali is added: OH - + Al 3+ \u003d Al (OH) 3 and its dissolution upon further addition: Al(OH) 3 + NaOH = Na |
| NH4+ | OH − , heating | Emission of gas with a pungent odor: NH 4 + + OH - \u003d NH 3 + H 2 O Blue wet litmus paper |
| H+ (acid environment) | Indicators: − litmus − methyl orange | Red staining |