The Pambak River in the Lori region in northern Armenia has acquired a reddish tint; water samples have been taken for examination.
In April 1999 After the NATO bombing of Yugoslavia and the destruction of petrochemical plants, a poisonous “black rain” fell over the town of Pancevo, containing a huge amount of heavy metals and organic compounds harmful to human life. The soil and groundwater were seriously contaminated, contaminated with ethylene and chlorine. A huge amount of oil, petroleum products, ammonia and amino acids ended up in the Danube.
In June-July 2000 in some areas 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. They exceeded the maximum permissible concentrations of cobalt (more than four times) and zinc (more than 434 times). Laboratory studies confirmed that the composition of the contaminated rain was identical chemical composition samples taken on the territory of Electrozinc OJSC, which violated the standards for maximum permissible 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.
In July-September 2001“red rains” have repeatedly fallen in the Indian state of Kerala. Several hypotheses were put forward for the origin of the red particles: some considered them to be red dust carried by the wind from the Arabian Desert, others recognized them as fungal spores or ocean algae. A version of their extraterrestrial origin was put forward. According to scientists' calculations, a total of about 50 tons of this strange substance fell to the ground along with precipitation.
In October 2001 got under abnormal rain residents of the southwestern regions of Sweden. After the rain, gray-yellow stains remained on the surface of the earth. Swedish experts, and in particular Lars Fransen, a researcher from the Gothenburg Geoscience Center, said that strong winds "sucked in" red sand dust from the Sahara, raised it to a height of 5 thousand meters and then dumped it with rain in Sweden.
Summer 2002 green rain fell over the Indian village of Sangranpur near the city of Kolkata. Local authorities announced that there was no chemical attack. An examination by scientists who arrived at the site determined that the green cloud is nothing more than flower and mango pollen contained in bee excrement and does not pose a danger to humans.
In 2003 In Dagestan, precipitation fell in the form of salt deposits. Cars parked under open air, covered with a layer of salt. According to meteorologists, the cause of this was a cyclone that came from the regions of Turkey and Iran. Small particles of sand and dust raised by a strong wind from quarries being developed in Dagestan mixed with water dust raised from the surface of the Caspian Sea. The mixture 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, it was observed by residents of Transcarpathia in the villages of Tikha and Gusinoye. According to one version, the reason for the orange color of the snow was sandstorms in Saudi Arabia: grains of sand, picked up by a strong wind, accumulated in the upper layers of the atmosphere and fell along with snow in Transcarpathia.
April 19, 2005 In the Kantemirovsky and Kalacheevsky districts of the Voronezh region, red rain fell. The precipitation left an unusual mark on the roofs of houses, fields, and agricultural equipment. The soil sample contained traces of ocher, a natural pigment for paint production. It contained hydroxides of iron and clay. Further investigation revealed that a release occurred at an ocher production plant in the village of Zhuravka, which led to the coloring of rain clouds red. According to experts, the precipitation did not pose a danger to the health of people and animals.
April 19, 2005 Over several districts 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 dark beige clothes, which were then not washed off. The same rain occurred on April 22 in Orel. The analyzes showed that the sediments contained alkali, namely nitrogenous compounds. The precipitation was very concentrated.
In April 2005 For several days, orange rains fell in Ukraine - in the Nikolaev region and in Crimea. Colored precipitation also covered the Donetsk, Dnepropetrovsk, Zaporozhye, and Kherson regions these days. Ukrainian weather forecasters said that the orange color of the rain was due to a dust hurricane. The wind brought dust particles from North Africa.
In February 2006 grey-yellow snow fell in the village of Sabo, located 80 km south of the city of Okha in northern Sakhalin. According to eyewitnesses, oily spots of a gray-yellow color and with an unusual strange smell formed on the surface of the water resulting from melting the suspicious snow. Experts believe that unusual precipitation could be the consequences of the activity of one of the Far Eastern volcanoes. Perhaps environmental pollution from the oil and gas industry is to blame. The cause of the yellowing of the snow has not been precisely determined.
February 24-26, 2006 In some areas of Colorado (USA), brown snow was falling, the color was almost like chocolate. “Chocolate” snow in Colorado is a consequence of a long drought in neighboring Arizona: giant clouds of dust mixing with snow appear there. Sometimes volcanic eruptions give the same result.
In March 2006 Creamy-pink snow fell in the north of Primorsky Krai. Experts explained unusual phenomenon the fact that the cyclone had previously passed through the territory of Mongolia, where at that time strong dust storms were raging, covering large areas of desert areas. Dust particles were caught in the cyclone's vortex and colored the precipitation.
March 13, 2006 V 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 warned that snow containing fine sand could be hazardous to the respiratory system.
November 7, 2006 In Krasnoyarsk, light snow fell with green rain. It walked for about half an hour and, having melted, turned into a thin layer of greenish clay. People exposed to green rain experienced watery eyes and headaches.
January 31, 2007 In the Omsk region, yellow-orange snow with a pungent odor, covered with oily spots, fell over an area of about 1.5 thousand square kilometers. Having passed through the entire Irtysh region, a plume of yellow-orange sediments reached the Tomsk region along the edge. But the bulk of the “acid” snow fell in the Tarsky, Kolosovsky, Znamensky, Sedelnikovsky and Tyukalinsky districts of the Omsk region. The colored snow exceeded the norm for iron content (according to preliminary laboratory data, the concentration of iron in the snow was 1.2 mg per cubic centimeter at the maximum permissible norm at 0.3 mg). According to Rospotrebnadzor, this concentration of iron is not dangerous to human life and health. Laboratories in Omsk, Tomsk and Novosibirsk were involved in the study of anomalous precipitation. It was initially assumed that the snow contained the toxic substance heptyl, which is a component of rocket fuel. The second version of the appearance of yellow precipitation was emissions from metallurgical enterprises in the Urals. However, Tomsk and Novosibirsk experts came to the same conclusion as Omsk ones - the unusual color of the snow is due to the presence of clay-sand dust, which could have entered the Omsk region from Kazakhstan. No toxic substances were found in the snow.
In March 2008 Yellow snow fell in the Arkhangelsk region. Experts have suggested that the yellow color of the snow is explained by natural factors. This is caused by the high content of sand that got into the clouds as a result of dust storms and tornadoes that occurred elsewhere on the planet.
Let's imagine this situation:
You are working in a laboratory and have decided to conduct 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 and safely remained 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 These are reactions that make it possible to distinguish one substance from another, as well as to find out the qualitative composition of unknown substances.
For example, it is known that cations of some metals, when their salts are added to the burner flame, color it a certain color:
This method can only work if the substances being distinguished change the color of the flame differently, or one of them does not change color at all.
But, let’s say, as luck would have it, the substances being determined do not color the flame, or color it 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 using any reagent?
There are two options:
- One substance reacts with the added reagent, but the second does not. In this case, it must be clearly visible that the reaction of one of the starting substances with the added reagent actually took place, that is, some external sign of it is observed - a precipitate formed, a gas was released, a color change occurred, etc.
For example, it is impossible to distinguish water from a solution of sodium hydroxide using hydrochloric acid, despite the fact that alkalis react well with acids:
NaOH + HCl = NaCl + H2O
This is due to the absence of any external signs of a reaction. A clear, colorless solution of hydrochloric acid when mixed with a colorless hydroxide solution forms the same clear solution:
But on the other hand, you can distinguish water from an aqueous solution of alkali, for example, using a solution of magnesium chloride - in this reaction a white precipitate forms:
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, you can distinguish a sodium carbonate solution from a silver nitrate solution using a hydrochloric acid solution.
hydrochloric acid reacts with sodium carbonate to release colorless gas without smell - carbon dioxide(CO 2):
2HCl + Na 2 CO 3 = 2NaCl + H 2 O + CO 2
and with silver nitrate to form a white cheesy precipitate AgCl
HCl + AgNO 3 = HNO 3 + AgCl↓
The tables below present various options detection of specific ions:
Qualitative reactions to cations
| Cation | Reagent | Sign of reaction |
| Ba 2+ | SO 4 2- | Ba 2+ + SO 4 2- = BaSO 4 ↓ |
| Cu 2+ | 1) Precipitation of blue color: Cu 2+ + 2OH − = Cu(OH) 2 ↓ 2) Black precipitate: Cu 2+ + S 2- = CuS↓ |
|
| Pb 2+ | S 2- | Black precipitate: 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↓ |
| Fe 2+ | 2) Potassium hexacyanoferrate (III) (red blood salt) K 3 | 1) Precipitation of a white precipitate that turns green in air: Fe 2+ + 2OH − = Fe(OH) 2 ↓ 2) Precipitation of a blue precipitate (Turnboole blue): K + + Fe 2+ + 3- = KFe↓ |
| Fe 3+ | 2) Potassium hexacyanoferrate (II) (yellow blood salt) K 4 3) Rodanide ion SCN − | 1) Brown precipitate: Fe 3+ + 3OH − = Fe(OH) 3 ↓ 2) Precipitation of blue precipitate (Prussian blue): K + + Fe 3+ + 4- = KFe↓ 3) The appearance of intense red (blood red) coloring: Fe 3+ + 3SCN − = Fe(SCN) 3 |
| Al 3+ | Alkali (amphoteric properties of hydroxide) | Precipitation of a white precipitate of aluminum hydroxide when adding a small amount of alkali: OH − + Al 3+ = Al(OH) 3 and its dissolution upon further pouring: Al(OH) 3 + NaOH = Na |
| NH4+ | OH − , heating | Emission of gas with a pungent odor: NH 4 + + OH − = NH 3 + H 2 O Blue turning of wet litmus paper |
| H+ (acidic environment) | Indicators: − litmus − methyl orange | Red staining |
Qualitative reactions to anions
| Anion | Impact or reagent | Sign of reaction. Reaction equation |
| SO 4 2- | Ba 2+ | Precipitation of a white precipitate, insoluble in acids: Ba 2+ + SO 4 2- = BaSO 4 ↓ |
| NO 3 − | 1) Add H 2 SO 4 (conc.) and Cu, heat 2) Mixture of H 2 SO 4 + FeSO 4 | 1) Formation of a blue solution containing Cu 2+ ions, release of brown gas (NO 2) 2) The appearance of color of nitroso-iron (II) sulfate 2+. Color ranges from violet to brown (brown ring reaction) |
| PO 4 3- | Ag+ | Precipitation of a light yellow precipitate in a neutral environment: 3Ag + + PO 4 3- = Ag 3 PO 4 ↓ |
| CrO 4 2- | Ba 2+ | Formation of a yellow precipitate, insoluble in acetic acid, but soluble in HCl: Ba 2+ + CrO 4 2- = BaCrO 4 ↓ |
| S 2- | Pb 2+ | Black precipitate: Pb 2+ + S 2- = PbS↓ |
| CO 3 2- | 1) Precipitation of a white precipitate, soluble in acids: Ca 2+ + CO 3 2- = CaCO 3 ↓ 2) The release of colorless gas (“boiling”), causing cloudiness of lime water: CO 3 2- + 2H + = CO 2 + H 2 O |
|
| CO2 | Lime water Ca(OH) 2 | Precipitation of a white precipitate and its dissolution with further passage of CO 2: Ca(OH) 2 + CO 2 = CaCO 3 ↓ + H 2 O CaCO 3 + CO 2 + H 2 O = Ca(HCO 3) 2 |
| SO 3 2- | H+ | Emission of SO 2 gas with a characteristic pungent odor (SO 2): 2H + + SO 3 2- = H 2 O + SO 2 |
| F − | Ca2+ | White precipitate: Ca 2+ + 2F − = CaF 2 ↓ |
| Cl − | Ag+ | Precipitation of a white cheesy precipitate, insoluble in HNO 3, but soluble in NH 3 ·H 2 O (conc.): Ag + + Cl − = AgCl↓ AgCl + 2(NH 3 ·H 2 O) = ) |