Chemistry colored precipitation. Abnormal precipitation: "colored" rains and "chocolate" snow

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 "druck" red sand 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 revealed that there had been a release at the ocher factory in the village of Zhuravka, which caused the rain clouds to turn 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.

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The precipitate is brown in color, but decomposes in the light with the release of finely dispersed metallic silver and acquires a dark gray (to black) color.

Chromate gives off a brown precipitate of MnCrO4, soluble in acids and ammonium salts.

Cobalt under the same experimental conditions gives a brown precipitate, but its formation is eliminated by potassium tartrate.

Silver ions with an alkali solution form a sparingly soluble silver oxide Ag2O - a brown precipitate. When an alkali solution is added to a complex silver salt, no precipitate is formed. For the formation of a precipitate, it is necessary that the product of the concentrations of ions [Ag 1 1OH - ] exceed the value of PRAgon 2 0 - Yu-8. In a solution of a complex salt, the concentration of silver ions is so low that PRdeon is not reached - Therefore, no precipitate is formed. Sulfur ions bind Ag ions, the concentration of the latter decreases, the equilibrium shifts towards the dissociation of the complex ion, which leads to its destruction.

Give an example of a salt soluble in water, which, when treated with alkali, produces a brown precipitate, and with sodium chloride, a white precipitate.

Sodium diethyldithiocarbamate (C2H5) 2NCS2Na in a slightly acidic or ammonia solution forms a suspension or brown precipitate with a copper (II) ion. This compound dissolves in organic solvents (amyl alcohol, amyl acetate, carbon tetrachloride), coloring them yellow-brown.

Already small amounts of (Hg2N) I SHO give the solution a yellowish color, and at a significant content - brown with a brown precipitate. The latter reaction is used in analytical practice to detect traces of ammonia and ammonium salts in solutions. An aqueous solution containing K2 [Hgl4] and KOH is called Nessler's reagent.

However, it should be remembered that they are prevented even by small amounts of C1 - ions, which reduce MnO ions to MnO (OH) 2 (brown precipitate. Meanwhile, when group III cations are precipitated, C ions open Mn by reaction with NaBiO3, which is carried out on cold, this almost does not interfere.Recall that the reactions with PbO2 and c succeed only with very small amounts of Mn (p.

The resulting solution of potassium manganate is poured into three test tubes. Add: to one - dilute acetic acid until the initial color of the solution changes to violet-red and a brown precipitate forms, to the other - chlorine water, to the third - an excess of sulfuric acid.

Salt waters leave a large residue of solids that are soluble in water and have a salty taste when they evaporate. Iron waters taste like ink and turn black from the infusion of ink nuts; remaining in the air, they usually secrete a ferruginous brown precipitate. Usually the character of mineral waters is mixed. The attached table provides an analysis of some of the mineral springs known for their special properties. The amount of substances is expressed in parts per million by weight [p.

It takes 1-2 weeks to complete the reaction. The reaction mixture is filtered through a loose paper filter into a beaker with 1000 ml of isobutyl alcohol. A brown precipitate precipitates. It is filtered off in vacuum through a glass filter with a porous plate No. 3, washed with diethyl ether and dried in a vacuum desiccator on a Petri dish at room temperature. The yield is almost quantitative.

Dissolve 0 25 - 1 0 g of the sample in 20 - 30 ml of aqua regia when heated; add water to 200 ml, 2 ml Fe (III) solution (10 mg / ml) (collector) and precipitate Fe (OH) 3 together with A1 (OH) 3 by the action of concentrated ammonia. In this case, a precipitate of molybdic acid H2Mo04 also precipitates, which is dissolved with an excess of ammonia, adding it dropwise. A brown precipitate remains. The solution was neutralized with HC1 (1:1) and ammonia was again added dropwise until a faint odor was added.

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Colored rains are often frightening with their appearance: while water of amazing color is pouring onto the ground, people usually immediately begin to frantically remember if there have been any recent chemical emissions from an industrial enterprise located nearby (it becomes especially scary if you are on street when the black rain was pouring down). In fact, red, white, yellow, green rain is by no means always associated with human anthropogenic activity and is often of a natural nature.

Colored rains consist of the most ordinary water drops, which, before spilling onto the ground, mixed with natural impurities. These can be leaves, flowers, small grains or sand brought into the upper layers of the atmosphere by a strong wind or a tornado, which gave the drops an interesting and unusual shade, for example, chalk particles create white rain.

Black, chocolate, red, green, yellow and white rain can fall everywhere - both on the European continent and in other parts of the globe. People have known about strange colored rains for a long time, Plutarch and Homer recalled them in their writings. You can also often find their description in medieval literature.

Rain with a red tint

Precipitation comes in different shades, but red rain makes a particularly shocking impression on people. Showers of this particular color have long been considered an unkind sign and a herald of an approaching war. Such precipitation has always been wary of both ordinary people and eminent philosophers of antiquity. For example, Plutarch, when writing about the red rain that fell on the earth's surface after the battles with the Germanic tribes, argued that the raindrops acquired their shade precisely due to the bloody fumes from the battlefield. According to him, it was they who saturated the air and gave the water drops a brown tone.

It is interesting that it is red rain that falls on the earth's surface most often (usually either in Europe or near the African continent). Why this is happening - for modern scientists has long been no mystery, and they do not see any mysticism in this phenomenon.

The reason for the red rain is the ordinary dust of the African desert (it is also called trade wind dust), which contains a huge amount of red microorganisms:

• A strong wind or tornado raises dust with red particles into the upper atmosphere, from where air currents carry it to the European continent.
• Over the European continent, dust mixes with water droplets and colors them.
• After that, drops in the form of rain fall down, surprising and astounding the local population.

This is far from the only explanation for this phenomenon. For example, a few years ago in India it rained red for two months (which could not but alarm the local population) - and African dust had nothing to do with it. Since during this period both the weather and the wind repeatedly changed their direction, while the showers almost did not stop.

The red rain also had a negative effect on the leaves, they quickly became not easily dry, but also acquired a dirty gray hue, after which they fell off - a phenomenon that is not typical for India at this time of the year.

The reasons for this phenomenon, scientists have put forward a variety of. There were suggestions that the impurities that color the rain red are of extraterrestrial origin and are associated with an exploding meteorite in the upper atmosphere, the microparticles of which mixed with precipitation. Another version, which was followed by more skeptical scientists, and with them the Indian government, said that the color of precipitation was quite strongly influenced by spores growing on algae trees from the lichen family, therefore, the red color of rain is absolutely harmless to living organisms.

Rain in black

Black rain falls much less frequently than red rain. It appears due to the mixing of water droplets with volcanic or cosmic (meteorite explosion) dust. Black rain is often dangerous - if the cause of its occurrence is industrial enterprises whose activities are related, for example, to burning coal or processing petroleum products.

For example, in the late 90s, during the period of hostilities in Yugoslavia, several petrochemical enterprises were destroyed, after which black rain fell, containing a lot of heavy metals and organic compounds harmful to human health and life. The black rain also had a negative impact on the environment, as soil, groundwater and one of the largest rivers in Europe, the Danube, were polluted.

snow white rain

For regions with chalk rocks, milky rain (white rain) is a fairly common phenomenon, since raindrops here often contain tiny particles of chalk and white clay. At the same time, white rain may well fall in other places on our planet.

For example, in the capital of a European city a few years ago there was a milky rain, after which not only white puddles appeared on the roads, but with a lot of foam, which extremely frightened the locals.

Experts have not been able to fully determine what exactly caused the appearance of such a phenomenon. Some agreed that the white rain fell due to the active construction of houses and roads, which was just taking place in the city during this period. Others have suggested that the milky rain was due to ragweed spores that were just flying in the air.

All experts unequivocally agreed that white rain is dangerous for the health of local residents, especially allergy sufferers, asthmatics, as well as people with lung and bronchial diseases.

Yellow and green precipitation

You can get under green or yellow rain when the pollen of various plants (both flowers and trees) mixes with water drops. For example, when mixed with particles of birch, green rain often falls. But in the Omsk and Arkhangelsk regions, water drops contain impurities of sand and clay, so yellow rain is often shed here.

More interesting cases can cause a similar phenomenon. For example, once a yellow rain fell on one of their villages in India, Sangrampur, causing panic among the local population. Fearing the presence of toxic substances in the sediments, tests were carried out, the result of which shocked scientists. It turned out that green, in some places - yellow rain - these are ordinary bee excrement (several swarms of bees flew in this area at once), in which traces of honey, pollen of flowers and mangoes were found.

Green rain can often fall due to the admixture of chemicals. For example, a few years ago it rained green in the Krasnoyarsk Territory. After that, people living in this region began to complain of severe headaches and tearing.

Despite the fact that colored rains are an interesting, surprising and impressive phenomenon, it is better not to fall under them: you never know what exactly the water drops were mixed with in each case. Well, if nature turned out to be the cause of such a phenomenon, then colored rain can even be good for health. But if you are unlucky, and you fall under, for example, white rain or black rain caused by an anthropogenic factor, this will definitely not be displayed in the best way on health.

Almost all chromium compounds and their solutions are intensely colored. Having a colorless solution or a white precipitate, we can conclude with a high degree of probability that chromium is absent. Compounds of hexavalent chromium are most often colored yellow or red, while trivalent chromium is characterized by greenish tones. But chromium is also prone to the formation of complex compounds, and they are painted in a variety of colors. Remember: all chromium compounds are poisonous.

Potassium dichromate K 2 Cr 2 O 7 is perhaps the most famous of the chromium compounds and is the easiest to obtain. A beautiful red-yellow color indicates the presence of hexavalent chromium. Let us carry out several experiments with it or with sodium dichromate very similar to it.

We strongly heat in the flame of a Bunsen burner on a porcelain shard (a piece of crucible) such an amount of potassium dichromate that will fit on the tip of a knife. Salt will not release water of crystallization, but will melt at a temperature of about 400 ° C with the formation of a dark liquid. Let's warm it up for a few more minutes on a strong flame. After cooling, a green precipitate forms on the shard. We will dissolve part of it in water (it will turn yellow), and leave the other part on the shard. The salt decomposed when heated, resulting in the formation of soluble yellow potassium chromate K 2 CrO 4, green chromium oxide (III) and oxygen:

2K 2 Cr 2 O 7 → 2K 2 CrO 4 + Cr 2 O 3 + 3/2O 2
Due to its tendency to release oxygen, potassium dichromate is a strong oxidizing agent. Its mixtures with coal, sugar or sulfur ignite vigorously on contact with the flame of a burner, but do not give an explosion; after combustion, a voluminous layer of green is formed - due to the presence of chromium oxide (III)-ash.

Carefully! Burn no more than 3-5 g on a porcelain shard, otherwise the hot melt may start to splatter. Keep your distance and wear safety goggles!

We scrape off the ash, wash it with water from potassium chromate and dry the remaining chromium oxide. Let's prepare a mixture consisting of equal parts of potassium nitrate (potassium nitrate) and soda ash, add it to chromium oxide in a ratio of 1:3 and melt the resulting composition on a crock or magnesia stick. Dissolving the cooled melt in water, we get a yellow solution containing sodium chromate. Thus, molten saltpeter oxidized trivalent chromium to hexavalent. By fusion with soda and saltpeter, all chromium compounds can be converted into chromates.

For the next experiment, let's dissolve 3 g of powdered potassium dichromate in 50 ml of water. To one part of the solution, add a little potassium carbonate (potash). It will dissolve with the release of CO2, and the color of the solution will become light yellow. Chromate is formed from potassium bichromate. If we now add a 50% solution of sulfuric acid in portions (Caution!), Then the red-yellow color of the bichromate will appear again.

Pour 5 ml of potassium dichromate solution into a test tube, boil with 3 ml of concentrated hydrochloric acid under draft or in the open air. Yellow-green poisonous chlorine gas is released from the solution, because chromate will oxidize HCl to chlorine and water. Chromate itself will turn into green trivalent chromium chloride. It can be isolated by evaporating the solution, and then, fusing with soda and nitrate, converted to chromate.

In another test tube, carefully add 1-2 ml of concentrated sulfuric acid to potassium dichromate (in an amount that fits on the tip of a knife). (Caution! The mixture may splatter! Wear safety goggles!) We heat the mixture strongly, as a result, brownish-yellow hexavalent chromium oxide CrOz is released, which is poorly soluble in acids and well in water. It is anhydride of chromic acid, but sometimes it is called chromic acid. It is the strongest oxidizing agent. Its mixture with sulfuric acid (chromium mixture) is used for degreasing, since fats and other difficult-to-remove contaminants are converted into soluble compounds.

Attention! Extreme care must be taken when working with the chromium mixture! If splashed, it can cause severe burns! Therefore, in our experiments, we will refuse to use it as a cleaning agent.

Finally, consider the reactions of detection of hexavalent chromium. Place a few drops of potassium dichromate solution in a test tube, dilute it with water and carry out the following reactions.

When a solution of lead nitrate is added (Caution! Poison!) Yellow lead chromate (chrome yellow) precipitates; when interacting with a solution of silver nitrate, a red-brown precipitate of silver chromate is formed.

Add hydrogen peroxide (properly stored) and acidify the solution with sulfuric acid. The solution will take on a deep blue color due to the formation of chromium peroxide. The peroxide, when shaken with some ether (Caution! Fire hazard!) will turn into an organic solvent and turn it blue.

The latter reaction is specific for chromium and is very sensitive. It can be used to detect chromium in metals and alloys. First of all, it is necessary to dissolve the metal. But, for example, nitric acid does not destroy chromium, as we can easily verify by using pieces of damaged chromium plating. With prolonged boiling with 30% sulfuric acid (hydrochloric acid can be added), chromium and many chromium-containing steels are partially dissolved. The resulting solution contains chromium (III) sulfate. To be able to conduct a detection reaction, we first neutralize it with caustic soda. Gray-green chromium (III) hydroxide will precipitate, which will dissolve in excess NaOH and form green sodium chromite.

Filter the solution and add 30% hydrogen peroxide (Caution! Poison!). When heated, the solution will turn yellow, as chromite is oxidized to chromate. Acidification will result in a blue color of the solution. The colored compound can be extracted by shaking with ether. Instead of the method described above, thin filings of a metal sample can be alloyed with soda and nitrate, washed, and the filtered solution tested with hydrogen peroxide and sulfuric acid.

Finally, let's test with a pearl. Traces of chromium compounds give a bright green color with brown.

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