“Matter and Energy” - Carbohydrates. Let's save our nature. Why do animals eat? Make a food web. Signs of a living organism. A family of tits eats 35 thousand caterpillars over the summer. Oxygen. The old man didn’t like the way the Owl hooted and sighed. Grif. The woodpecker's knocking and bird voices will immediately fall silent. Make a food chain. Grass. Fats. Cold-blooded.
“Properties of living matter” - Reflection: Levels of organization of life: Criteria of life: Study new topic. Why are there many concepts of “LIFE”, but there is not one short and generally accepted one? How do the properties of living things manifest themselves at different levels of organization? Highlight the main features of the concept “ Biological system" Organizing time.
“Amount of substance” - Molar mass is numerically equal to the relative molecular mass of the substance. How many structural units are contained in 1 mole? Epigraph. 1. Measure 12 tablespoons of water into a measuring cylinder. It is measured in g/mol. Shows the mass of 1 mole of a substance. Lesson - research: “Amount of substance. It has numeric value 6.02 · 1023.
“Matter” - Currently, just over a hundred types of atoms are known. What if there are no clouds, but the Sun is shining? Draw appropriate conclusions. Carrying out. Use the dictionary to find the definition of “extraction.” Similarly (carefully!), evaporate 3–4 ml of sugar solution. On Earth you almost never encounter physical substances.
“Substance in chemistry” - Gaseous substances. Chemical. Acetone. Carbon dioxide. Ability to react with other substances. Physical. Choose the right word. Properties of substances. Simple substances. Liquid substances. Complex substances. Water. Oxygen. Today we begin to study one of the most ancient of important sciences - chemistry.
“Classification of substances” - Classification of substances. Acidic. It is not a hydroxide: Eliminate the substance that is superfluous according to the classification characteristics. Mass fractions elements in the compound are equal: potassium - 43.1%, chlorine - 39.2%, oxygen - 17.7%. Simple substances - metals. Distribute the substances. Silver. Metals and non-metals. Carbon.
Task C2 of the Unified State Examination in Chemistry is a description chemical experiment, according to which you will need to create 4 reaction equations. According to statistics, this is one of the most difficult tasks; a very low percentage of those passing it cope with it. Below are recommendations for solving task C2.
Firstly, in order to correctly solve task C2 of the Unified State Exam in chemistry, you need to correctly imagine the actions to which substances are subjected (filtering, evaporation, roasting, calcination, sintering, fusion). It is necessary to understand where a physical phenomenon occurs with a substance, and where a chemical reaction occurs. The most commonly used actions with substances are described below.
Filtration - a method of separating heterogeneous mixtures using filters - porous materials that allow liquid or gas to pass through, but retain solids. When separating mixtures containing a liquid phase, a solid substance remains on the filter; filtrate .
Evaporation - the process of concentrating solutions by evaporating the solvent. Sometimes evaporation is carried out until saturated solutions are obtained, with the aim of further crystallizing from them a solid in the form of a crystalline hydrate, or until the solvent has completely evaporated in order to obtain the dissolved substance in its pure form.
Calcination –
heating a substance to change it chemical composition. Calcination can be carried out in air or in an inert gas atmosphere. When calcined in air, crystalline hydrates lose water of crystallization, for example, CuSO 4 ∙5H 2 O→CuSO 4 + 5H 2 O
Thermally unstable substances decompose:
Cu(OH) 2 →CuO + H 2 O; CaCO 3 → CaO + CO 2
Sintering, fusion –
This is the heating of two or more solid reagents, leading to their interaction. If the reagents are resistant to oxidizing agents, then sintering can be carried out in air:
Al 2 O 3 + Na 2 CO 3 → 2NaAlO 2 + CO 2
If one of the reagents or the reaction product can be oxidized by air components, the process is carried out in an inert atmosphere, for example: Cu + CuO → Cu 2 O
Substances that are unstable to the action of air components oxidize when heated and react with air components:
2Сu + O 2 → 2CuO;
4Fe(OH) 2 + O 2 →2Fe 2 O 3 + 4H 2 O
Burning - process heat treatment, leading to combustion of the substance.
Secondly, knowledge of the characteristic features of substances (color, smell, state of aggregation) will serve as a hint or check for the correctness of the actions performed. Below are the most characteristic features gases, solutions, solids.
Signs of gas:
Painted: Cl 2 – yellow-green; NO 2 – brown; O 3 – blue (all have smells). All are poisonous, dissolve in water, Cl 2 And NO 2 react with her.
Colorless, odorless: H 2, N 2, O 2, CO 2, CO (poison), NO (poison), inert gases. All are poorly soluble in water.
Colorless with odor: HF, HCl, HBr, HI, SO 2 (pungent odors), NH 3 ( ammonia) – highly soluble in water and poisonous, PH 3 (garlic), H 2 S (rotten eggs) – slightly soluble in water, poisonous.
Colored solutions:
Yellow: Chromates, for example K 2 CrO 4, solutions of iron (III) salts, for example FeCl 3.
Orange: Bromine water, alcohol and alcohol-water solutions of iodine (depending on the concentration of yellow before brown), dichromates, for example, K 2 Cr 2 O 7
Green: Hydroxo complexes of chromium (III), for example, K 3, nickel salts (II), for example NiSO 4, manganates, for example, K 2 MnO 4
Blue: Copper (II) salts, for example CuSO 4
From pink to purple: Permanganates, e.g. KMnO 4
From green to blue: Chromium (III) salts, for example CrCl 3
Colored sediments:
Yellow: AgBr, AgI, Ag 3 PO 4, BaCrO 4, PbI 2, CdS
Brown: Fe(OH) 3 , MnO 2
Black, black-brown: Sulfides of copper, silver, iron, lead
Blue: Cu(OH) 2 , KFe
Green: Cr(OH) 3 – gray-green, Fe(OH) 2 – dirty green, turns brown in air
Other colored substances:
Yellow : sulfur, gold, chromates
Orange: copper oxide (I) – Cu 2 O, dichromates
Red: bromine (liquid), copper (amorphous), red phosphorus, Fe 2 O 3, CrO 3
Black: СuO, FeO, CrO
Gray with a metallic sheen: Graphite, crystalline silicon, crystalline iodine (when sublimated - purple pairs), most metals.
Green: Cr 2 O 3, malachite (CuOH) 2 CO 3, Mn 2 O 7 (liquid)
Thirdly, when solving C2 tasks in chemistry, for greater clarity, it can be recommended to draw up transformation schemes or the sequence of the resulting substances.
And finally, in order to solve such problems, you need to clearly know the properties of metals, non-metals and their compounds: oxides, hydroxides, salts. It is necessary to repeat the properties of nitric and sulfuric acids, potassium permanganate and dichromate, redox properties various connections, electrolysis of solutions and melts of various substances, decomposition reactions of compounds different classes, amphotericity, hydrolysis of salts.
Calcination is the operation of heating solids until high temperature(above 400° C) for the purpose of: a) getting rid of volatile impurities; b) achievements constant mass; c) carrying out reactions occurring at high temperatures; d) ashing after preliminary combustion of organic substances. Heating to high temperatures is carried out in furnaces (muffle or crucible). Very often in laboratories it is necessary to calcinate substances such as CaCl2*bH2O, Na2SO4*10H2O, etc., for the purpose of dehydration. Calcination is usually carried out on gas stoves, the substance is placed on steel frying pans. If contamination of the preparation with iron cannot be allowed, then it should be calcined in fireclay plates or frying pans. Never need to be placed in a frying pan a large number of salt, since during dehydration the salt scatters, which causes significant losses.
If you have to heat something in a porcelain or fireclay crucible, then the crucible is heated gradually: first on a small flame, then the flame is gradually increased. To avoid losses during ignition, crucibles are usually covered with lids. If you have to ashes something in such a crucible, then first, with low heating, burn the substance in an open crucible and only then close the crucible with a lid.
If the porcelain crucible is dirty inside after work, then to clean it, pour concentrated nitric acid or fuming hydrochloric acid into it and carefully heat it. If neither nitric nor hydrochloric acids remove contamination, then take a mixture of them in the following proportions: nitric acid - 1 volume and hydrochloric acid - 3 volumes. Sometimes contaminated crucibles are treated either with a concentrated solution of KHSO4 when heated, or by melting this salt in a crucible and then washing it with water. There are, however, cases when all of the above techniques do not help; This type of crucible, which cannot be cleaned, is recommended to be used for some non-essential work.
In the practice of analytical work, when it is necessary to calcinate metal oxides, for example PerOz, care must be taken to ensure that the burner flame does not come into contact with the substance being calcined (to avoid reduction). In such cases, platinum plates are used with a hole in the center into which a crucible is inserted. .These plates can be strengthened in asbestos cardboard. Instead of platinum, you can also use clay or fireclay plates with round hole in the center.
When calcining the precipitate in Gooch's crucible the latter is inserted into an ordinary one, several large sizes porcelain crucible so that the walls of both crucibles do not touch. To do this, the Gooch crucible is wrapped in a strip of moistened asbestos and, pressing, pressed into the safety crucible so that the distance between the bottom of both is equal to several millimeters. First, everything is dried together at 100 ° C, then the Gooch crucible is removed, and the safety crucible along with the asbestos ring is strongly calcined before the first use.
Platinum crucibles require very careful handling and are often burned through by inexperienced workers. To avoid this, heating platinum cookware on a bare flame must be carried out so that the inner cone of the burner flame does not touch the platinum. When this cone comes into contact with platinum, platinum carbide is formed. Severe destruction of platinum occurs at a temperature close to its melting point.
Minor surface damage is eliminated by heating in an oxidizing environment. A badly damaged crucible, together with the resulting platinum carbide powder (which must be collected), is handed over for remelting.
If the platinum crucible becomes dirty, it should be cleaned by heating pure nitric acid (without traces of hydrochloric acid) in it. If this does not help, KHSO4 or NaHS04 is melted in a crucible. When this does not achieve the goal, the walls of the crucible are wiped with the finest quartz (white) sand or fine emery (No. LLC).
Quartz crucibles are very convenient because they have many valuable properties, such as: high thermal strength, chemical indifference to most substances, etc. However, you must remember that quartz is alloyed with alkalis or alkaline salts.
In some cases, calcination or heating must be carried out either in an oxidizing, or reducing, or neutral environment. Most often, tubular or special furnaces are used for these purposes, through which the corresponding gas is passed from a cylinder during calcination. To create an oxidizing environment, oxygen is passed through, and to create a reducing environment, hydrogen or carbon monoxide is passed through. A neutral atmosphere is created by passing argon
Rice. 231. Split oven for heating to high temperature.
and sometimes nitrogen. When deciding which gas should be used in each individual case, you need to know whether the selected gas will not react with a given substance at high temperatures. Even so it would seem inert gas, like nitrogen, under certain conditions can form compounds such as nitrides.
For calcination using gas burners A split stove is very convenient (Fig. 231). It is made from two fireclay or diatomite bricks, hollowing out recesses of the same size in them so that when the bricks are placed on top of each other, a chamber is formed inside. A hole with a diameter of 15 mm is drilled in the center of the top brick, and 25 mm in the center of the bottom brick. In the plane of contact of the bricks, grooves are made to strengthen the porcelain triangle in which the crucible is placed.
By heating this furnace with a Teklu or Mecker burner, you can reach a temperature of up to 1100 ° C. The temperature is adjusted by changing the distance of the furnace from the burner.
When calcination in a platinum crucible is not possible, so-called “soda” crucibles can be used. Finely crushed and pre-calcined sodium carbonate is poured into a porcelain crucible, for example No. 4, up to half its height. A smaller crucible is then pressed into the salt.
Rice. 232 Forming soda crucibles
Place overnight in a muffle furnace that is turned off after heating. By morning, the soda crucible is ready and alkaline melting can be carried out in it, for example, some ores or minerals. Na2CO3 melts at a temperature of 870° C; therefore, the “soda” crucible can be heated up to 600° C.
The condition of task C2 on the Unified State Exam in chemistry is a text describing the sequence of experimental actions. This text needs to be converted into reaction equations.
The difficulty of such a task is that schoolchildren have little idea of experimental, non-paper chemistry. Not everyone understands the terms used and the processes involved. Let's try to figure it out.
Very often, concepts that seem completely clear to a chemist are perceived incorrectly by applicants. Here short dictionary such concepts.
Dictionary of obscure terms.
- Hitch- this is simply a certain portion of a substance of a certain mass (it was weighed on the scales). It has nothing to do with the canopy over the porch :-)
- Ignite- heat the substance to a high temperature and heat until the end of the chemical reactions. This is not “mixing with potassium” or “piercing with a nail.”
- “They blew up a mixture of gases”- this means that the substances reacted explosively. Usually an electric spark is used for this. The flask or vessel in this case don't explode!
- Filter- separate the precipitate from the solution.
- Filter- pass the solution through a filter to separate the precipitate.
- Filtrate- this is filtered solution.
- Dissolution of a substance- This is the transition of a substance into solution. It can occur without chemical reactions (for example, when sodium chloride NaCl is dissolved in water, a solution of sodium chloride NaCl is obtained, rather than alkali and acid separately), or during the dissolution process the substance reacts with water and forms a solution of another substance (when barium oxide is dissolved, it can occur barium hydroxide solution). Substances can be dissolved not only in water, but also in acids, alkalis, etc.
- Evaporation- this is the removal of water and volatile substances from a solution without decomposing the solids contained in the solution.
- Evaporation- This is simply reducing the mass of water in a solution by boiling.
- Fusion- this is the joint heating of two or more solid substances to a temperature when their melting and interaction begins. It has nothing to do with river swimming :-)
- Sediment and residue.
These terms are very often confused. Although these are completely different concepts.
“The reaction proceeds with the release of a precipitate”- this means that one of the substances obtained in the reaction is slightly soluble. Such substances fall to the bottom of the reaction vessel (test tubes or flasks).
"Remainder"- is a substance that left, was not completely consumed or did not react at all. For example, if a mixture of several metals was treated with acid, and one of the metals did not react, it may be called the remainder. - Saturated a solution is a solution in which, at a given temperature, the concentration of a substance is the maximum possible and no longer dissolves.
Unsaturated a solution is a solution in which the concentration of a substance is not the maximum possible; in such a solution you can additionally dissolve some more amount of this substance until it becomes saturated.
Diluted And "very" diluted solution is a very conditional concept, more qualitative than quantitative. It is assumed that the concentration of the substance is low.
For acids and alkalis the term is also used "concentrated" solution. This is also a conditional characteristic. For example, concentrated hydrochloric acid is only about 40% concentrated. And concentrated sulfuric acid is an anhydrous, 100% acid.
In order to solve such problems, you need to clearly know the properties of most metals, non-metals and their compounds: oxides, hydroxides, salts. It is necessary to repeat the properties of nitric and sulfuric acids, potassium permanganate and dichromate, redox properties of various compounds, electrolysis of solutions and melts of various substances, decomposition reactions of compounds of different classes, amphotericity, hydrolysis of salts and other compounds, mutual hydrolysis of two salts.
In addition, it is necessary to have an idea of the color and state of aggregation of most of the substances being studied - metals, non-metals, oxides, salts.
That is why we analyze this type of assignment at the very end of the study of general and inorganic chemistry.
Let's look at a few examples of such tasks.
Example 1: The product of the reaction of lithium with nitrogen was treated with water. The resulting gas was passed through a solution of sulfuric acid until the chemical reactions stopped. The resulting solution was treated with barium chloride. The solution was filtered, and the filtrate was mixed with sodium nitrite solution and heated.
Solution:
Example 2:Weighed aluminum was dissolved in dilute nitric acid, and a gaseous simple substance was released. Sodium carbonate was added to the resulting solution until gas evolution completely stopped. Dropped out the precipitate was filtered And calcined, filtrate evaporated, the resulting solid the rest was melted down with ammonium chloride. The released gas was mixed with ammonia and the resulting mixture was heated.
Solution:
Example 3: Aluminum oxide was fused with sodium carbonate, and the resulting solid was dissolved in water. The resulting solution was passed through sulphur dioxide until the interaction ceases completely. The precipitate that formed was filtered off, and bromine water was added to the filtered solution. The resulting solution was neutralized with sodium hydroxide.
Solution:
Example 4: Zinc sulfide was treated with a solution of hydrochloric acid, the resulting gas was passed through an excess of sodium hydroxide solution, then a solution of iron (II) chloride was added. The resulting precipitate was fired. The resulting gas was mixed with oxygen and passed over the catalyst.
Solution:
Example 5: Silicon oxide was calcined with a large excess of magnesium. The resulting mixture of substances was treated with water. This released a gas that was burned in oxygen. The solid combustion product was dissolved in a concentrated solution of cesium hydroxide. Hydrochloric acid was added to the resulting solution.
Solution:
Tasks C2 from the Unified State Examination in Chemistry for independent work.
- Copper nitrate was calcined, and the resulting solid precipitate was dissolved in sulfuric acid. Hydrogen sulfide was passed through the solution, the resulting black precipitate was fired, and the solid residue was dissolved by heating in concentrated nitric acid.
- Calcium phosphate was fused with coal and sand, then the resulting simple substance was burned in excess oxygen, the combustion product was dissolved in excess caustic soda. A barium chloride solution was added to the resulting solution. The resulting precipitate was treated with excess phosphoric acid.
- Copper was dissolved in concentrated nitric acid, the resulting gas was mixed with oxygen and dissolved in water. Zinc oxide was dissolved in the resulting solution, then a large excess of sodium hydroxide solution was added to the solution.
- Dry sodium chloride was treated with concentrated sulfuric acid with low heating, and the resulting gas was passed into a solution of barium hydroxide. A solution of potassium sulfate was added to the resulting solution. The resulting sediment was fused with coal. The resulting substance was treated with hydrochloric acid.
- A sample of aluminum sulfide was treated with hydrochloric acid. At the same time, gas was released and a colorless solution was formed. An ammonia solution was added to the resulting solution, and the gas was passed through a lead nitrate solution. The resulting precipitate was treated with a solution of hydrogen peroxide.
- Aluminum powder was mixed with sulfur powder, the mixture was heated, the resulting substance was treated with water, a gas was released and a precipitate was formed, to which an excess of potassium hydroxide solution was added until completely dissolved. This solution was evaporated and calcined. To received solid matter added excess hydrochloric acid solution.
- The potassium iodide solution was treated with a chlorine solution. The resulting precipitate was treated with a solution of sodium sulfite. A solution of barium chloride was first added to the resulting solution, and after separation of the precipitate, a solution of silver nitrate was added.
- Gray-green powder of chromium (III) oxide was fused with an excess of alkali, the resulting substance was dissolved in water, resulting in a dark green solution. Hydrogen peroxide was added to the resulting alkaline solution. The result is a yellow solution, which, when sulfuric acid is added, becomes Orange color. When hydrogen sulfide is passed through the resulting acidified orange solution, it becomes cloudy and turns green again.
- (MIOO 2011, training work) Aluminum was dissolved in a concentrated solution of potassium hydroxide. The resulting solution was passed through carbon dioxide until precipitation stops. The precipitate was filtered and calcined. The resulting solid residue was fused with sodium carbonate.
- (MIOO 2011, training work) Silicon was dissolved in a concentrated solution of potassium hydroxide. Excess hydrochloric acid was added to the resulting solution. The cloudy solution was heated. The resulting precipitate was filtered and calcined with calcium carbonate. Write the equations for the reactions described.
Answers to tasks for independent solution:
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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 substances are converted into new reaction products. These products are gaseous, because the candle decreases in size. Combustion is accompanied by the release of heat and light.
Melting paraffin, as mentioned above, refers to physical phenomena. 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. Reaction condition – influx fresh air(if you stop it, 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.