Calcination of the dry residue allows you to determine the approximate ratio of the mineral and organic parts of the contaminants. The ratio of the weight of ash to the weight of the dry residue is called the ash content of the dry residue and is expressed as a percentage.[...]
Calcination is the combustion of waste, carried out in order to reduce the volume and mass of the reacting components. However, during the calcination process, waste is generated (ash and slag, flue gases, fly ash and wastewater generated during ash handling and cleaning flue gases), which have a harmful effect on environment. Therefore, calcination is not the best way elimination of solid organic waste.[...]
Calcination is the third, very important operation in the production of TiO2, since it is during calcination that the product acquires the necessary pigment properties. During calcination, due to the decomposition of basic titanium sulfates, water and E03 are removed from metatitanic acid. Practice has established that some products with a low content of BOS are more difficult to isolate than TiO304, and in the presence of impurities, for example K2504, the removal of BOS is facilitated and begins already at 480°. [...]
When calcining the charge, it is necessary to strictly observe temperature regime process, since when the temperature rises to 750-800°, brown and even black, so-called “rusty spots,” begin to appear on the surface of the melt. With a further increase in temperature, these spots spread over the entire surface, and then throughout the entire mass of the melt. If there is a lack of boric acid in the charge or if it is poorly mixed with chromium, brown areas can also form on the melt, but they consist of undecomposed chromium, are highly soluble in water and are not identical with “ rusty spots", appearing as a result of the decomposition of the melt. After calcination is completed, the melt is unloaded from the furnace onto iron trays, on which it is cooled. The charge is loaded into the furnace in very small quantities due to its strong swelling during calcination. For example, in an electric furnace with a hearth surface of 0.5 m2 it is possible to load only 10-15 kg of charge, from which 1.5-2.5 kg of finished pigment is obtained. Calcination of the emerald green mixture lasts 1.5-2 hours.[...]
When calcining an empty membrane filter, so little ash is obtained that it can be neglected in the calculation.[...]
Calcination temperature 500-600°. The color of the pigment is established at this temperature after 20-30 minutes, but in practice the duration of calcination reaches up to 2 hours, since with a shorter duration, undestroyed impurities remain in the pigment. [...]
Residue after calcination. To determine the residue after calcination of coarse impurities (“calcined coarse impurities”), the weighed membrane filter is removed with crucible tongs or tweezers and very carefully burned over a porcelain crucible, previously calcined and weighed. [...]
Residue after calcination. It is recommended to heat a porcelain or quartz crucible with filtered coarse impurities in an electric muffle furnace at 600 °C for 10-15 minutes. The content of the residue after ignition is calculated using the formula given in section “A” (see page 20).[...]
The ignition residue is determined as described in section “A” (see page 20).[...]
Precipitation and calcination conditions have a great influence on the pigment properties of cadmium sulfide, i.e. its color, hiding power, intensity, stability, etc. [...]
Dry residue and loss on ignition. In water treatment practice, dry residue is understood as the total amount of inorganic and organic compounds in a dissolved and colloidally dissolved state. The dry residue is determined by evaporating a pre-filtered sample followed by drying at 10 °C. Loss on ignition determines the content of organic substances in the dry residue. The residue after calcination characterizes the salt content of water.[...]
The essence of the process comes down to calcination of apatite (with the addition of 2-8% silica) or Kara-Tauz phosphorite (with the addition of lime) at 1400-1450° in the presence of water vapor. Under these conditions it is destroyed crystal cell apatite and fluorine are removed by 90%. Phosphates of various compositions are obtained that are soluble in weak acids. When processing apatite, the fertilizer contains 30-32% P205, when calcining phosphorite - 20-22%; 70-92% of these phosphates are soluble in 2% citric acid. It has been established that in equal doses of P2O superphosphate and defluorinated phosphate with the main application give a similar effect. Defluorinated phosphate is also used for mineral fertilizing animals.[...]
Ash content is determined by combustion and calcination of the filter with sludge after determining the concentration of activated sludge. The difference between the weight of the dry matter of the activated sludge and the weight of the ash characterizes the organic part of the activated sludge - loss of heat upon ignition.[...]
A mixture of 60% CoO and 40% ZnO, after calcination, almost entirely consists of the ZnCo204 compound. With a lower cobalt content, dark green products are formed, which are a mixture of ZnCo204 with zinc oxide.[...]
A distinction is made between total dry residue and residue after calcination. The term “total dry residue” refers to the amount of substance remaining after evaporation of a wastewater sample and drying to a constant mass. The amount of substance obtained after calcination of the dry residue is called “calcination residue.” By reducing the mass of the dry residue after calcination, one can judge the content of organic substances in wastewater. The bitch residue is determined according to standard PN-59/Z-04519.[...]
The mechanism of the formation of red cadmium during calcination of a mixture of sulfur, selenium and cadmium salt is probably the following: at 250-300°, dissociation of cadmium carbonate or oxalate occurs into carbon dioxide and cadmium oxide. The latter is formed in a very active, reactive state and immediately interacts with sulfur and selenium, forming a red mass with a strong brown tint. This mass contains a certain amount of cadmium sulfur and selenide in the form of their mixture (Cs1 4-C [...]
Blacks are products obtained by calcination without air access of various organic substances of animal and plant origin. [...]
The volatile solids content is determined by calcining the residue at 550°C in an electric muffle furnace. The remainder of drinking and natural water, as well as sludge, is calcined for 1 hour, while the remainder of wastewater samples requires only a 20-minute calcination. Mass loss on ignition is expressed in mg of volatile matter per liter, and the residue after ignition is called non-volatile solids. The evaporation dish used in volatile solids analysis and the fiberglass filter disk must be subjected to pre-treatment by calcination in a muffle furnace to determine the exact initial self-weight. Volatile solids in wastewater are often interpreted as a measure of organic matter content. However, this is not entirely accurate, since the combustion of many organic substances produces ash, and many inorganic salts volatilize during the calcination process.[...]
The technological process for producing red iron oxide by calcination of ferric oxide or ferrous oxide hydrate consists of the following operations: preparation of ferric oxide or ferrous oxide hydrate, washing, filtering and drying the resulting hydrate and, finally, calcination of the dry or wet precipitate at 600-700°. [...]
Inner diameter retort 2.7 m, useful height (zone of drying, calcination and cooling of coal) 15.1 m. Total retort height 26 m. [...]
The total dry residue is also of mineral origin, loss on ignition is 8%. The concentration of chlorides and sulfates is relatively low, but the concentration of silicic acid salts is very significant (-300 mg! l) due to the flotation reagent used liquid glass. Cyanide, copper and arsenic are contained in small quantities. A very significant contamination is the organic reagents used in flotation: petroleum products, terpineol, xanthate (or dithiophosphate), which increase the oxidability of water to more than 100 mg/l O. [...]
To identify the dependence of the activity of kaolin on the temperature of its calcination, Budnikov and Gulinova measured the heat of its interaction with calcium oxide hydrate. They established that limit temperature calcination, above which the activity of kaolin decreases, is a temperature of the order of 800°. The practice of ultramarine production also confirms that kaolins calcined at temperatures above 800° are more difficult to react with ultramarine formation.[...]
The process of producing cadmium yellow using this method consists of the following operations: preparing and calcining the charge, washing, drying, grinding and sifting the pigment.[...]
The waters are turbid, yellowish in color, with a pH from 6.7 to 9.5. The loss of coarse impurities and total dry residue during calcination is negligible, which indicates the predominance of minerals(ore particles). The basis of dissolved mineral salts in the general runoff are sulfates. When wastewater passes through the tailings pond, the amount of coarse impurities decreases sharply. [...]
Most old method Determining the total content of organic impurities consists of determining loss on ignition. By calcining the residue obtained after evaporation of the sample at 110°C, many organic substances (carbohydrates, protein compounds) can be detected by the dark color of the residue and its charring. Loss on ignition also gives an indication of the presence of certain inorganic substances.[...]
Cadmium sulfide, formed during precipitation with hyposulfite, has a medium yellow color with a very lively and bright tint. When the pigment is calcined to 500°, its color does not change, but at 550-600° it becomes slightly lighter.[...]
The precipitate is calcined in a muffle furnace at a temperature of 700-750°C; at temperatures above 800°, the precipitate decomposes into BaO and O3. The duration of the first calcination is 30 minutes, the second one is 20 minutes[...]
Of all the sorbents, the best is activated aluminum oxide. It is made from commercial aluminum oxide. This reagent is activated by double calcination at 800° C with intermediate cooling and wetting with a 15% soda solution. The height of the sorbent layer in the filter should be about 2 m. Its working exchange capacity (according to Vodgeo) is 1.25 kg of fluorine per 1 m3 of sorbent. [...]
When calcining the sludge at the firing temperature of the tiles, i.e., at 900 °C, diffraction maxima were discovered that can be attributed to Fe304. The spent activated sludge contains iron and nickel hydroxides; after calcination, reflections appeared that can be identified as M1re204 - nickel spinel. [...]
After drying the precipitated suspension at a temperature of 105 °C and weighing, the content (in mg/l) of precipitated substances is determined. The ratio of the mass of the remaining ash after calcination of the dry sediment at a temperature of 600 ° C to the total mass of absolutely dry sediment (in%) is called the ash content of the latter. The loss of burnt substances during ignition determines the amount of ash-free substance.[...]
Of the described methods for producing cadmium yellow, the greatest practical use have: interaction of cadmium carbonate with sodium sulfide, calcination of cadmium carbonate with sulfur and interaction of cadmium salt with hyposulfite. When working using these methods, it is possible to obtain yellow cadmium of all shades - from lemon to orange. Orange cadmium is also formed when cadmium carbonate is calcined with a mixture of sulfur and selenium. This method is described below. Precipitation of yellow cadmium is carried out in wooden, porcelain or enamel tanks, calcination - in muffle or rotary kilns.[...]
Some of these water-soluble salts contained in the pigment may even cause accelerated corrosion themselves. For example, mars made by calcining iron sulfate may contain small amounts of non-calcined sulfate, which is a very strong corrosive agent. Therefore, before use, it is necessary to check the chemical composition of mars and, in particular, the content of iron sulfate in them, although such an analysis does not make it possible to judge other properties of this pigment, for example, hiding power, etc. Chemical composition pigments, however, it is important to know not only for judging the quality of pigments and the strength and durability of films prepared from them, but also because some substances that make up pigments have a harmful effect on human body.[ ...]
The use of extraction for oil sludge regeneration showed that the moisture content of the resulting sludge ranges from 65-75%. When neutralizing this sludge by calcination in drum furnaces, heat inputs are required that are almost equal to the heat that can be obtained from the petroleum product separated from oil sludge. Therefore, the utilization of petroleum products from oil sludge in in this case is unprofitable.[...]
Thus, when producing cadmium sulfide, a very large number of factors can change, namely: the initial cadmium and sulfide salts, precipitation and calcination conditions, etc., as a result of which there may be a very large number of ways to obtain cadmium sulfide of a certain color and properties. And, indeed, in different time many methods have been proposed for producing cadmium sulfide suitable for use as a pigment.[...]
Progress of determination. Into the same test tube that was used in the manufacture of the scale, pour 10 ml of the test water, taken either directly or after evaporating it, calcining the dry residue, dissolving it in water, neutralizing phenolphthalein with nitric acid and diluting to a certain volume (see the previous method ). Add 1.00 ml of mercury(II) nitrate solution and 2 drops of diphenylcarbazide solution. After 10-15 minutes, the resulting color is compared with the colors of the scale solutions, examining the solutions from above. [...]
The first report of iron blue was made in 1710, but it did not contain information about the method of its production. The method for producing iron blue was published only in 1724 and consisted of calcining ox blood with potash and precipitating the acidified aqueous extract of this melt with iron sulfate and alum. Later (in 1735) it was found that instead of blood, other substances of animal origin could be used - horn, claws, hair, skin, etc.[...]
Chemical pollution is determined by chemical analysis of wastewater, establishing temperature, color, odor, transparency, sediment by volume and weight, suspended solids by weight and loss on ignition, dense residue on ignition, oxidability, chemical oxygen demand (COD), biochemical demand in oxygen (BOD), nitrogen of general and ammonium salts, pH reaction, acidity and alkalinity, chlorides, phosphates, sulfates, concentration of acid salts, phenols, cyanides, rhodonides, heavy metal salts and other chemical impurities.[...]
As can be seen from the above data, the main pollutants in the wastewater of molybdenum-tungsten enrichment plants are coarse impurities of mineral origin, since the loss on ignition is only 4.5% of the total amount. When passing through the tailings pond, the concentration of impurities in the total runoff is reduced by only 70%, i.e. the water is poorly clarified and transparency increases only to 2.1 cm.[...]
The process of water softening by sedimentation produces 200 tons of sludge with a specific gravity of 1.5, and 15% (by weight) of the sludge consists of solid particles, which are calcium and magnesium salts. Since calcium salts, when calcined, form calcium oxide, which can be used in the process of water softening, the pre-compacted sludge is sent to the furnace. In this case, in the process of compaction (centrifugation), 70% of the solid material of the sludge is separated, the compacted sludge - centrate - contains 65% (by weight) of the solid material.[...]
Studies have shown that petroleum cokes are quite reactive with respect to atmospheric oxygen even at moderate reaction temperatures (520°C) up to pre-calcination temperatures of 800-1200°C. At oxidation temperatures above 540°C (see Table I), calcined coke ignites and the process moves from the kinetic reaction region to the diffusion region, where coke combustion is determined by the supply of oxygen. It follows from this that the combustion of coke dust must be carried out at temperatures above 550+600°C. [...]
One of possible solutions The problem is the chemical-metallurgical method developed in our country, which produces two products of sodium monochromate and ferrochrome as a metallurgical product. Sodium monochromate is obtained by calcining a charge consisting of chrome ore, soda ash and a solid residue (without dolomite). After calcination, the cake is subjected to leaching, which results in the formation of a solution of sodium monochromate and a solid residue in the form of granules containing 30-35% chromium oxide.[...]
The color of cadmium sulfide obtained by this method is golden yellow. Cadmium sulfide of other shades, namely; lemon, light yellow and orange - it is not possible to obtain this method, since changing the ratio between the reagents, as well as the calcination conditions, does not affect the color of cadmium sulfide.[...]
Wastewater gravity processing plants, in technological process which flotation reagents are not used are contaminated with coarse impurities (flotation tailings, sludge, sand), consisting of waste rock accompanying the floated minerals. The loss during calcination of coarse impurities of gravity factories is 2.5% of their total amount.[...]
In a batch process, the heat of the heating fluid in the second half of the retort revolution is poorly used. This can be avoided by constructing a vertical continuous retort, in which fresh firewood is fed to the top of the retort and, moving from top to bottom under the influence of its own weight, encounters steam and gases more and more high temperature. In this case, the raw material gradually passes through the zones of drying, dry distillation, calcination of coal and its cooling.
The filtered and washed sediment still contains moisture; it is usually dried and calcined. These operations make it possible to obtain a substance with a strictly defined chemical composition.Drying the sediment. The precipitate is dried together with the filter. Cover the funnel with the sediment with a piece of damp filter paper. Its edges are pressed tightly against the outer surface of the funnel, and excess paper is removed. The result is a paper lid that fits tightly on the funnel and protects the sediment from dust.
After this, the funnel with the sediment should be placed in drying cabinet having shelves with round holes. A funnel is inserted into one of them. The temperature in the cabinet is maintained no higher than 90-105 ° C - with stronger heating, the filter chars and disintegrates.
Precipitates are ignited in porcelain crucibles various sizes. Before you begin calcination, you need to know the mass of the empty crucible. To do this, the crucible is first calcined to a constant mass, that is, until its mass stops changing. The crucibles are heated in an electric muffle furnace, in crucible furnace or at gas burner, but always under the same temperature conditions under which the precipitate is supposed to be calcined. The calcination temperature is approximately judged by the color of the heat of the muffle (crucible) furnace:
| Beginning of dark red heat.................................... | ~525°С |
| Dark red heat............................................... ...... | -7000C |
| Light red heat.................................................... ..... | -900 - 10000C |
| Light orange glow.................................................... | ~1200°С |
| White heat................................................... ............. | -13000C |
| Dazzling white heat.................................................... | -1400 - 15000C |
The crucible intended for calcination is taken by the edge with crucible tongs and placed in a muffle furnace. After 25-30 minutes of calcination, it is removed from the oven, allowed to cool on a sheet of asbestos (or on granite tiles) and transferred to a desiccator. The latter is not closed with a lid immediately, but after 1-2 minutes; otherwise, when cooling, a vacuum is created in the desiccator and the lid will be difficult to open. Then the desiccator is taken to the weighing room and left for 15-20 minutes so that the crucible reaches the temperature of the balance.
After weighing the crucible on an analytical balance, it is heated again for 15-20 minutes, cooled in a desiccator and weighing is repeated. If the result of the last weighing differs from the previous one by no more than ±0.0002 g, it is considered that the crucible has been adjusted to a constant mass, i.e., it is prepared for calcination of the sediment. Otherwise, the crucible is heated, cooled and weighed again. The results of all weighings must be recorded in the laboratory journal.
Calcination of the sediment. Crystallization or constitutional water, which even dried sediment may contain, must be completely removed by calcination. In addition, during calcination, chemical decomposition of the substance often occurs. For example, calcium oxalate CaC2O4.H2O, obtained by precipitation of Ca2+ ions with ammonium oxalate, loses water of crystallization when dried:
CaC2O4. H2O → CaC2O4 + H2O
When heated slightly, it releases carbon monoxide and turns into calcium carbonate:
CaC2O4 → CO2 + CaCO3
Finally, when strongly heated, calcium carbonate decomposes to form carbon dioxide and calcium oxide:
CaCO3 → CaO + CO2
Based on the mass of calcium oxide, the result of the determination is calculated. The temperature and duration of calcination of sediments may vary.
In the calcination technique itself, two cases are distinguished.
1. Calcination of the sediment without separating the filter. This method is used when the calcined sediment does not interact with the carbon of the charred filter. Thus, without removing the filter, precipitates of oxides Al2O3, CaO and some others are calcined.
A porcelain crucible, brought to a constant mass, is placed on glossy (preferably black) paper. Carefully remove the dried filter with sediment from the funnel and, holding it over the crucible, roll it up. After this, carefully place it in the crucible. If, upon careful inspection, traces of sediment are found on the funnel, then wipe it thoroughly. inner surface it with a piece of ashless filter, which is placed in the same crucible. Finally, grains of sediment that spilled onto the paper when rolling up the filter are also shaken off into the crucible. Then place the crucible on electric stove and carefully ashes (burns) the filter. Sometimes, instead, the crucible is inserted into a porcelain triangle on a tripod ring and heated over a small burner flame. It is desirable that the filter slowly chars and decays without bursting into flames, since combustion leads to the loss of the smallest particles of sediment. If it does catch fire, then under no circumstances do they blow out the flame, but only stop heating it and wait until the burning stops.
Having finished ashing the filter, transfer the crucible to a muffle furnace and calcinate it for 25-30 minutes. Cool the crucible in a desiccator, weigh it and record its mass in a laboratory notebook. Repeat calcination (15-20 min), cooling and weighing until a constant mass of the crucible with sediment is achieved.
2. Calcination of the sediment with filter separation. This method is used when the sediment, when charring the filter, can chemically interact with carbon (recover). For example, a precipitate of silver chloride AgCl is reduced by carbon to free silver; It cannot be heated together with the filter.
The well-dried sediment is poured out of the filter as completely as possible onto glossy paper and covered with a beaker (or an inverted funnel) to prevent loss. The filter with the sediment particles remaining on it is placed in a crucible (brought to a constant mass), burned and calcined. The previously separated precipitate is added to the calcined residue in the same crucible. After this, as usual, the contents of the crucible are calcined to constant weight.
If the precipitate is filtered using a glass crucible, then instead of calcination, drying is used to a constant mass. Of course, the filter crucible must first be brought to a constant mass at the same temperature.
If during the analysis an irreparable error is made (for example, part of the sediment is lost, part of the solution with sediment is spilled, etc.), then the determination should be started again without wasting time on obtaining a deliberately incorrect result.
Weighing
Weighing is carried out on analytical balances with an accuracy of 10-6 g (VLR 200)
The filtered and washed sediment still contains moisture; it is usually dried and calcined. These operations make it possible to obtain a substance with a strictly defined chemical composition.
Drying the sediment. The precipitate is dried together with the filter. Cover the funnel with the sediment with a piece of damp filter paper. Its edges are pressed tightly against the outer surface of the funnel, and excess paper is removed. The result is a paper lid that fits tightly on the funnel and protects the sediment from dust.
After this, the funnel with the sediment should be placed for 20-30 minutes in a drying cabinet with shelves with round holes. A funnel is inserted into one of them. The temperature in the cabinet is maintained no higher than 90-105 ° C - with stronger heating, the filter chars and disintegrates.
The precipitates are calcined in porcelain crucibles of various sizes. Before you begin calcination, you need to know the mass of the empty crucible. To do this, the crucible is first calcined to a constant mass, that is, until its mass stops changing. The crucibles are calcined in an electric muffle furnace, in a crucible furnace or on a gas burner, but always under the same temperature conditions under which the sediment is supposed to be calcined. The calcination temperature is approximately judged by the color of the heat of the muffle (crucible) furnace:
The crucible intended for calcination is taken by the edge with crucible tongs and placed in a muffle furnace. After 25-30 minutes of calcination, it is removed from the oven, allowed to cool on an asbestos sheet (or on a granite tile) and transferred to a desiccator. The latter is not closed with a lid immediately, but after 1-2 minutes; otherwise, when cooling, a vacuum is created in the desiccator and the lid will be difficult to open. Then the desiccator is taken to the weighing room and left for 15-20 minutes so that the crucible reaches the temperature of the balance.
After weighing the crucible on an analytical balance, it is heated again for 15-20 minutes, cooled in a desiccator and weighing is repeated. If the result of the last weighing differs from the previous one by no more than ±0.0002 g, it is considered that the crucible has been adjusted to a constant mass, i.e., it is prepared for calcination of the sediment. Otherwise, the crucible is heated, cooled and weighed again. The results of all weighings must be recorded in the laboratory journal.
Calcination of the sediment.Crystallization or constitutional water, which even dried sediment may contain, must be completely removed by calcination. In addition, during calcination, chemical decomposition of the substance often occurs. For example, calcium oxalate CaC 2 O 4 H 2 O, obtained by precipitation of Ca 2+ ions with ammonium oxalate, loses water of crystallization when dried:
CaC 2 O 4 H 2 O → CaC 2 O 4 + H 2 O
When heated slightly, it releases carbon monoxide and turns into calcium carbonate:
CaC 2 O 4 → CO 2 + CaCO 3
Finally, when strongly heated, calcium carbonate decomposes to form carbon dioxide and calcium oxide:
CaCO 3 → CaO + CO 2
Based on the mass of calcium oxide, the result of the determination is calculated. The temperature and duration of calcination of sediments may vary.
In the calcination technique itself, two cases are distinguished.
1. Calcination of sediment without separating the filter. This method is used when the calcined sediment does not interact with the carbon of the charred filter. Thus, without removing the filter, precipitates of oxides Al 2 O 3, CaO and some others are calcined.
A porcelain crucible, brought to a constant mass, is placed on glossy (preferably black) paper. Carefully remove the dried filter with sediment from the funnel and, holding it over the crucible, roll it up. After this, carefully place it in the crucible. If, upon careful inspection, traces of sediment are found on the funnel, then carefully wipe its inner surface with a piece of ashless filter, which is placed in the same crucible. Finally, grains of sediment that spilled onto the paper when rolling up the filter are also shaken off into the crucible. Then place the crucible on an electric stove and carefully ashes (burns) the filter. Sometimes, instead, the crucible is inserted into a porcelain triangle on a tripod ring and heated over a small burner flame. It is desirable that the filter slowly chars and decays without bursting into flames, since combustion leads to the loss of the smallest particles of sediment. If it does catch fire, then under no circumstances do they blow out the flame, but only stop heating it and wait until the burning stops.
Having finished ashing the filter, transfer the crucible to a muffle furnace and calcinate it for 25-30 minutes. Cool the crucible in a desiccator, weigh it and record its mass in a laboratory notebook. Repeat calcination (15-20 min), cooling and weighing until a constant mass of the crucible with sediment is achieved.
2. Calcination of sediment with filter separation. This method is used when the sediment, when charring the filter, can chemically interact with carbon (recover). For example, a precipitate of silver chloride AgCl is reduced by carbon to free silver; It cannot be heated together with the filter.
The well-dried sediment is poured out of the filter as completely as possible onto glossy paper and covered with a beaker (or an inverted funnel) to prevent loss. The filter with the sediment particles remaining on it is placed in a crucible (brought to a constant mass), burned and calcined. The previously separated precipitate is added to the calcined residue in the same crucible. After this, as usual, the contents of the crucible are calcined to constant weight.
If the precipitate is filtered using a glass crucible, then instead of calcination, drying is used to a constant mass. Of course, the filter crucible must first be brought to a constant mass at the same temperature.
If during the analysis an irreparable error is made (for example, part of the sediment is lost, part of the solution with sediment is spilled, etc.), then the determination should be started again without wasting time on obtaining a deliberately incorrect result.
This lesson is a practical exercise during which various experiments are carried out, representing both physical and chemical processes. The chemical reactions carried out are given characteristics indicating the conditions for the onset and occurrence of the reactions, as well as their characteristics.
Topic: Initial chemical ideas
Lesson: Practical lesson 3. Chemical reactions
EXPERIENCE 1.
Place a piece of paraffin on a metal plate and heat it. As a result, we observe a change in the aggregate state of paraffin (transition to a liquid state). Despite the fact that the molten paraffin has become colorless (changed color), this phenomenon is considered physical, because the composition of the substance remained the same, only its state of aggregation changed.
Rice. 1. Melting paraffin
EXPERIENCE 2.
Let's light a candle and let it burn a little. As the candle burns, the wick and paraffin burn, and part of the paraffin melts, heating up from the heat generated during the combustion process. The combustion of wick and paraffin are chemical processes, because... starting materials transform into new reaction products. These products are gaseous, because the candle decreases in size. Combustion is accompanied by the release of heat and light.
The melting of paraffin, as mentioned above, is a physical phenomenon. Let us characterize the process of burning a candle. The conditions for the start of the reaction are ignition and contact of the wick with air. The condition for the reaction to occur is the influx of fresh air (if it is stopped, the candle will go out). Signs of a reaction are the release of heat and light.
2. Electronic version of the journal “Chemistry and Life” ().
Homework
With .14-15 №№ 9, 10 from the Workbook in Chemistry: 8th grade: to the textbook by P.A. Orzhekovsky and others. “Chemistry. 8th grade” / O.V. Ushakova, P.I. Bespalov, P.A. Orzhekovsky; under. ed. prof. P.A. Orzhekovsky - M.: AST: Astrel: Profizdat, 2006.
To completely remove volatile substances resulting from thermal decomposition, calcination is used, which can be carried out using a gas burner flame, in muffle or crucible furnaces. To calcinate the substance in a burner flame, it is placed in a metal or porcelain crucible. It is then inserted into the porcelain triangle so that it fits 2/3 of its height into the triangle. The porcelain triangle is placed on the tripod ring. Calcination is carried out in a fume hood.
Muffle furnaces are used for calcination of substances at elevated temperatures (up to 1600 °C). Reagents must not be spilled in the furnace working area. The hot crucibles are removed from the muffle furnace using long crucible tongs.
Filtration
This is the process of movement of a liquid or gas through a porous partition, which is accompanied by the deposition of solids suspended in them on the porous partition.
particles. The effectiveness of the filtration process is measured by the speed and completeness of separation of solid particles from liquid or gas. It is influenced by: viscosity (liquids with low viscosity are easier to filter), temperature (the higher the temperature, the easier the solution is filtered, since the viscosity of the liquid decreases when heated), pressure (the greater the pressure difference on both sides of the filter, the higher the speed filtration), particle size and nature solid(the larger the particle size compared to the pore size of the filter, the faster and easier the filtration is).
Various organic and inorganic substances are used as filter materials. It must be remembered that for filtering you cannot use materials that interact in any way with the filtered liquid. For example, alkalis, especially concentrated ones, cannot be filtered through a filter made of pressed glass and other materials containing silicon dioxide, since SiO 2 dissolves in alkalis. Filter materials can be: fibrous (wadding, wool, various fabrics, synthetic fibers), granular (quartz sand), porous (paper, ceramics). The choice of filter material depends on the requirements for the purity of the solution, as well as on its properties.
Filtration can be carried out in various ways: in normal conditions, when heated, under vacuum. Under normal conditions, glass funnels are used for filtering. Some filter material, such as cotton wool or filter paper, is placed inside the funnel. Filter paper is used to make simple or pleated filters.
To prepare a simple filter, take a sheet of filter paper square shape. Fold first in half, then again, as shown in Figure a:
The result is a square reduced by 4 times. The corner of the folded square is cut along an arc with scissors. Separate one layer of paper from the other three with your finger and straighten it.
To prepare a pleated filter, first proceed in the same way as when making a simple one, then fold it in half and bend each half several times in one direction and the other like an accordion (Fig. b). The top edge of the filter should not reach the edge of the funnel by 5 mm. The filter, correctly placed in the funnel, is moistened with the filtered liquid or distilled water.
When filtering, the funnel is mounted on a ring stand. The tip of the funnel should touch the wall of the filtrate vessel.
The liquid is poured over a glass rod, pressing it against the wall of the funnel. If it is necessary to filter a hot solution, then use a special funnel for hot filtering with electric or water heating.
Filtration under reduced pressure (under vacuum) allows for more complete separation of solids from liquids. 
liquid and increase the speed of the process. To do this, assemble a device consisting of a filtering device - a Buchner funnel (1) connected to a Bunsen flask (2), the Buchner flask is connected to the pump via a rubber hose. The size of the Buchner funnel should correspond to the mass of the sediment, but not the liquid. Place two circles of filter paper on the mesh bottom of the Buchner funnel, moisten them with distilled water, connect the device to the pump, ensuring that the filter fits tightly to the funnel mesh. The filtering process begins. First, pour most of the liquid onto the filter, then shake the remaining liquid with the sediment and pour the mixture into a funnel. When filtering, the precipitate should not overfill the funnel, and the filtrate in the Bunsen flask should not reach the extension connecting the flask to the safety flask. At the end of filtration, first turn off the pump, then remove the funnel from the flask, and remove the precipitate onto a sheet of filter paper.
