Part I
1. Chemical phenomena, or chemical reactions, are phenomena in which the transformation of one substance into another occurs.
2. The formation of new substances is accompanied by the appearance of new signs or properties, characterizing these substances, which can be fixed with the help of the senses, i.e. notice signschemical reactions.
3. Fill in the table "Signs of chemical reactions."
4. Classification of reactions on the basis of the release or absorption of heat.
5. Conditions for the flow of chemical reactions:
- contact of reacting substances;
- initial heating for some exothermic reactions;
- constant heating for endothermic reactions.
Part II
1. In what case can we say that a chemical reaction is taking place?
1) Phenolphthalein indicator is poured into a test tube with an alkali solution.
3) Methyl orange indicator is poured into a test tube with an alkali solution.
Explain the answer.
Since in these cases a change in the color of the solution is observed, in 1 - the solution will become raspberry, in 3 - yellow.
2. Read the poem carefully.
Showed a series of signs in a row
We, decomposing, bichromate:
Color, sound, fire and even gas
Each of us could notice.
For the transformation to begin
We had to set fire to the crystals.
Heat outside is exo
Burning is light
Heat inside is endo -
Reverse thermal effect!
What signs of the described reaction are mentioned in the poem?
Discoloration, gas formation, odor.
If this reaction was not demonstrated to you in the lesson, find the video clip “The Decomposition of Ammonium Dichromate” on the Internet, watch it and make a drawing inspired by this wonderful reaction.
3. Establish a correspondence between the sign and the chemical reaction.
4. When preparing a solution of sulfuric acid, you should:
2) add sulfuric acid to water.
Explain the answer.
A large amount of heat is released, the water can boil and throw splashes on the face and hands of the worker.
5. Are the following statements correct?
A. Exothermic reactions, as a rule, proceed with constant heating.
B. Endometrial reactions can proceed without heating.
4) both judgments are wrong.
6. To increase the rate of a chemical reaction between solid and gaseous substances, you need crush the solid.
7. To increase the rate of a chemical reaction between solid soluble substances, you need crush and dissolve them in water.
8. Specify what needs to be done to eliminate the fire:
1) solid substances and materials - cover with dense material;
2) oil products - use a fire extinguisher;
3) electrical appliances - de-energize and cover with dense material.
In industry, such conditions are selected so that the necessary reactions are carried out, and harmful ones are slowed down.
TYPES OF CHEMICAL REACTIONS
Table 12 shows the main types of chemical reactions according to the number of particles involved in them. Drawings and equations of reactions often described in textbooks are given. decomposition, connections, substitution and exchange.
At the top of the table are decomposition reactions water and sodium bicarbonate. A device for passing a direct electric current through water is shown. The cathode and anode are metal plates immersed in water and connected to an electric current source. Due to the fact that pure water practically does not conduct electricity, a small amount of soda (Na 2 CO 3) or sulfuric acid (H 2 SO 4) is added to it. When current passes through both electrodes, gas bubbles are released. In the tube where hydrogen is collected, the volume is twice as large as in the tube where oxygen is collected (you can verify its presence with a smoldering splinter). The model scheme demonstrates the reaction of water decomposition. Chemical (covalent) bonds between atoms in water molecules are destroyed, and hydrogen and oxygen molecules are formed from the released atoms.
Model scheme compound reactions metallic iron and molecular sulfur S 8 shows that as a result of the rearrangement of atoms during the reaction, iron sulfide is formed. In this case, the chemical bonds in the iron crystal (metallic bond) and the sulfur molecule (covalent bond) are destroyed, and the released atoms combine to form ionic bonds into a salt crystal.
Another reaction of the compound is the slaking of lime CaO with water to form calcium hydroxide. At the same time, burnt (quicklime) lime begins to warm up and a loose powder of slaked lime is formed.
To substitution reactions refers to the interaction of a metal with an acid or salt. When a sufficiently active metal is immersed in a strong (but not nitric) acid, hydrogen bubbles are released. The more active metal displaces the less active metal from its salt solution.
typical exchange reactions is a neutralization reaction and a reaction between solutions of two salts. The figure shows the preparation of barium sulfate precipitate. The course of the neutralization reaction is monitored using the phenolphthalein indicator (crimson color disappears).
Table 12
Types of chemical reactions
AIR. OXYGEN. COMBUSTION
Oxygen is the most common chemical element on Earth. Its content in the earth's crust and hydrosphere is presented in Table 2 "The prevalence of chemical elements". Oxygen accounts for approximately half (47%) of the mass of the lithosphere. It is the predominant chemical element in the hydrosphere. In the earth's crust, oxygen is present only in bound form (oxides, salts). The hydrosphere is also represented mainly by bound oxygen (part of the molecular oxygen is dissolved in water).
The atmosphere of free oxygen contains 20.9% by volume. Air is a complex mixture of gases. Dry air is 99.9% nitrogen (78.1%), oxygen (20.9%) and argon (0.9%). The content of these gases in the air is almost constant. The composition of dry atmospheric air also includes carbon dioxide, neon, helium, methane, krypton, hydrogen, nitric oxide (I) (diazot oxide, nitrogen hemioxide - N 2 O), ozone, sulfur dioxide, carbon monoxide, xenon, nitrogen oxide ( IV) (nitrogen dioxide - NO 2).
The composition of the air was determined by the French chemist Antoine Laurent Lavoisier at the end of the 18th century (Table 13). He proved the content of oxygen in the air, and called it "vital air". To do this, he heated mercury on a furnace in a glass retort, the thin part of which was placed under a glass cap, lowered into a water bath. The air under the cap turned out to be closed. When heated, mercury combined with oxygen, turning into red mercury oxide. The "air" remaining in the glass cap after heating the mercury contained no oxygen. The mouse, placed under the cap, suffocated. Having calcined mercury oxide, Lavoisier again isolated oxygen from it and again received pure mercury.
The oxygen content in the atmosphere began to noticeably increase about 2 billion years ago. As a result of the reaction photosynthesis a certain volume of carbon dioxide was absorbed and the same volume of oxygen was released. The figure in the table schematically shows the formation of oxygen during photosynthesis. During photosynthesis in the leaves of green plants containing chlorophyll, when solar energy is absorbed, water and carbon dioxide are converted into carbohydrates(sugar) and oxygen. The reaction of the formation of glucose and oxygen in green plants can be written as follows:
6H 2 O + 6CO 2 \u003d C 6 H 12 O 6 + 6O 2.
The resulting glucose becomes insoluble in water. starch that accumulates in plants.
Table 13
Air. Oxygen. Combustion
Photosynthesis is a complex chemical process that includes several stages: the absorption and transport of solar energy, the use of sunlight energy to initiate photochemical redox reactions, the reduction of carbon dioxide and the formation of carbohydrates.
Sunlight is electromagnetic radiation of different wavelengths. In the chlorophyll molecule, when visible light (red and violet) is absorbed, electrons transition from one energy state to another. Photosynthesis consumes only a small part of the solar energy (0.03%) reaching the Earth's surface.
All carbon dioxide available on Earth goes through the cycle of photosynthesis in an average of 300 years, oxygen - in 2000 years, ocean water - in 2 million years. At present, a constant oxygen content has been established in the atmosphere. It is almost completely spent on respiration, combustion and decay of organic matter.
Oxygen is one of the most active substances. Processes involving oxygen are called oxidation reactions. These include combustion, breathing, decay and many others. The table shows the combustion of oil, which goes with the release of heat and light.
Combustion reactions can bring not only benefits, but also harm. Combustion can be stopped by stopping the air (oxidizer) from reaching the burning object with foam, sand, or a blanket.
Foam fire extinguishers are filled with a concentrated solution of baking soda. When it comes into contact with concentrated sulfuric acid, which is in a glass ampoule at the top of the fire extinguisher, carbon dioxide foam is formed. To activate the fire extinguisher, turn over and hit the floor with a metal pin. In this case, the sulfuric acid ampoule breaks and the carbon dioxide formed as a result of the reaction of the acid with sodium bicarbonate foams the liquid and throws it out of the fire extinguisher with a strong jet. Foamy liquid and carbon dioxide, enveloping the burning object, push the air and extinguish the flame.
Similar information.
The lesson is preceded by an excursion to the historical and ethnographic museum in the open air “Tukay Kyrlay”, with a visit to the house-museum of G. Tukay.
Learning objectives. To form knowledge about the signs and conditions of chemical reactions, on this basis to improve the ability to distinguish physical processes from chemical ones.
Development tasks. To improve the ability to explain the dependence of the course of chemical reactions on external conditions.
Experiment. Melting of paraffin, charring of starch, burning of a torch, interaction of sodium hydroxide with hydrochloric acid in the presence of phenolphthalein, interaction of copper sulfate (II) and sodium hydroxide, interaction of solutions of sodium carbonate and hydrochloric acid.
Planned learning outcomes. Students should be able to use examples of specific chemical reactions to indicate the conditions for their occurrence and further course, as well as signs of reactions.
Planned results of development. Students should be able to explain the relationship between conditions and the possibility of chemical reactions.
The lesson begins with students reading the poems of G. Tukay in the Tatar language, the criterion for the selection of poems is the reflection in them of various natural phenomena
In the process of demonstrating experiments (melting of paraffin, carbonization of starch), we find out the essence of the occurring phenomena and compile a table.
To consolidate knowledge, we conduct a conversation with students and answer questions.
Golden foliage swirled
In the pinkish water of the pond.
Like butterflies, a light flock with
Fading flies to the star ...
Teacher questions:
1. What phenomenon in the life of plants is mentioned in the poems of S. Yesenin?
2. Is leaf fall related to physical or chemical phenomena?
3. What is the reason for the change in the color of tree leaves in autumn, what physical or chemical phenomena occur in this case?
4. What pigment causes the green color of plant leaves?
5. What process occurs in the green leaves of plants under the action of sunlight?
Student message. Photosynthesis is a chemical phenomenon (the photosynthesis reaction equation is written on the blackboard).
To develop students' skills in self-control of knowledge, we conduct a test control.
1. Chemical phenomena (as opposed to physical ones) include:
- Combustion of gasoline in a car engine
- sour milk,
- snow melting,
- frost formation on trees.
2. Which of the natural phenomena are accompanied by chemical reactions?
- Rainfall,
- volcanic eruption,
- rotting plant residues,
- ice drift on the river.
3. Which of the signs are characteristic of chemical reactions?
- sediment formation,
- change in aggregate state,
- gas release,
- pulverization of matter.
4. Physical phenomena (unlike chemical ones) include:
- burning coal,
- preparation of powder from a piece of chalk,
- rust formation,
- the glow of a tungsten filament in a light bulb.
Teacher. Why do we need to know the conditions for the occurrence and conditions for the occurrence of chemical reactions?
Student. In order to control the course of chemical reactions, sometimes a chemical reaction must be stopped, for example, in a fire, we seek to stop the combustion reaction.
Student message. A forest fire is an uncontrolled burning of vegetation that spontaneously spreads through a forest area. Forest fires annually occur in the forests of Tatarstan, as well as in other countries of the world over vast areas and often take on the character of a natural disaster. Forest fires destroy the forest fund of Tatarstan, and also pose a danger to the population. In this case, there is an immediate threat of destruction by fire of settlements and objects of the national economy located near forests, as well as strong smoke and gas contamination of territories, even remote from the edge of the forest.
“The smoke was so plentiful that the birds could not soar, they fell to the ground”
The total forest area of the Republic of Tatarstan is 1270.3 thousand hectares, including 1165.3 thousand hectares covered with forests, of which 281.1 thousand hectares are forest crops. The total stock of timber is 168.8 million m 3 . Average wood growth - 4.13 m 3 / ha
Almost all forest fires in Tatarstan occur due to human negligence.
The fire season of 2004 in Tatarstan began on 20 April. During this time, forests burned more than 40 times in the republic, the press service of the Main Directorate of Natural Resources and Environmental Protection told Intertat.ru. It is noteworthy that out of 41 cases of forest fires, 39 are associated with violations by citizens of the requirements of the Fire Safety Rules in the forests of the Russian Federation.
To consolidate and generalize knowledge, students answer questions.
1. What are the conditions for the onset and cessation of combustion?
2. What fire extinguishing agents should be used in the following cases:
a) the clothes on the person caught fire;
b) gasoline ignited;
c) there was a forest fire;
d) did oil catch fire on the surface of the water?
In the final part of the lesson, the teacher sums up the lesson, the students receive homework.
Let's consider how knowledge about the conditions for the occurrence and course of a chemical reaction should be developed in chemistry lessons in grades VII-VIII.
In the first lessons, it is enough if students learn that under the same conditions one substance undergoes a chemical transformation, and the other does not (heating of stearin and sugar), that under certain conditions only a physical change occurs with a substance, and under others, a chemical (dissolving and heating sugar).
After familiarization with the signs of a chemical reaction, the first generalization of knowledge about the conditions of chemical interaction is carried out, organized as follows. Students are invited to answer the question: What conditions are needed in order for: a) sugar to char, b) magnesium to catch fire, c) a copper plate to become covered with a black coating? In all these cases, they call the same condition - the heating of substances. Discussing the answers, the teacher notes that for the combustion of Magnesium and the blackening of the copper plate, heating alone is not enough, it is necessary for the metals to come into contact with atmospheric oxygen. For confirmation, he shows the incandescence of a piece of shiny thin sheet of copper, folded in the form of an envelope with tightly pressed edges or thick copper wires twisted together. After cooling, it turns out that the copper turned black on the outside, but remained shiny on the inside, since oxygen molecules did not penetrate here.
The teacher demonstrates a solution of copper sulphate in a glass cylinder, on which a dilute solution of ammonium hydroxide was carefully poured from above. He draws attention to the appearance of a bright blue color only in the middle part of the vessel and says that a chemical reaction, starting at the place where the liquids come into contact with each other, can occur in the entire volume only if stirring is applied. Students develop their first ideas about such conditions of chemical interaction as the contact of reactants and their mixing.
In conclusion, they note that the most important conditions for a chemical reaction are: 1) the presence of substances that can undergo chemical transformations, 2) contact and mixing of substances (if the reaction occurs between two substances), 3) heating.
To test and consolidate knowledge, the following questions and tasks are used:
- Name the conditions necessary for chemical reactions. Give examples. What is the significance of knowing these conditions for practice?
- What conditions were necessary for: a) copper to become covered with a black coating, b) lime water to become cloudy?
- What conditions for the occurrence of a chemical reaction do we create when we light a spirit lamp or a gas burner? Which of these conditions are we violating when we extinguish the flame?
When studying the next topic - "Initial information about the structure and composition of substances" - the teacher pays attention to the conditions of those transformations that are used to form the concept of the decomposition reaction and the compound reaction. Emphasizes that for the decomposition of mercury oxide and basic copper carbonate, constant heating is necessary, and for the decomposition of water, the action of an electric current. The combination of sulfur with iron begins only when heated, and then, since heat is released during this reaction, further heating of the mixture is no longer necessary.
Students should learn that not all decomposition reactions proceed with the absorption of heat and not every combination of substances is accompanied by its release. The teacher shows an experiment: he heats a test tube with ammonium dichromate only until the reaction starts, which continues after the heating stops. The heating of a substance, the ejection of hot particles from the test tube, shows that the reaction proceeds with the release of heat.
Then an example of a combination reaction proceeding with the absorption of heat is given: the combination of nitrogen with oxygen occurs at a temperature above 1200 ° C and requires constant heating.
Further development and consolidation of knowledge about the conditions of chemical reactions takes place in the topic "Oxygen. Air".
After studying the chemical properties of oxygen, students are asked questions:
- What conditions are necessary for burning charcoal; sulfur, phosphorus and magnesium in oxygen and in the air? Why is it enough to heat these substances only until the reaction starts?
- Why is a piece of cork attached to the tip of the feather before burning a steel feather in oxygen? Is heat released when iron reacts with oxygen? Why do you think so?
- What are the combustion conditions and how do we create them when we light gas on a gas stove?
When students study the composition of air, they can be offered the following tasks and questions:
- Compare the conditions: a) for the formation of a red powder of mercury oxide in Lavoisier's experiment and b) for the decomposition of mercury oxide. What are the similarities and differences between these conditions?
- Why does the formation of mercury oxide stop when mercury is heated for a long time in a closed vessel with air? What condition of mercury oxidation is violated?
- A burning candle was placed in a large jar of air, then the jar was closed with a cork. The candle burned for a while and then went out. Why did the fire stop? What condition of interaction of substances was violated?
In the topic "Hydrogen" it is useful to analyze why in the Kipp apparatus, when the tap is closed, the reaction stops, what condition of the reaction is violated.
In the topic "Water. Solutions" they consider the chemical properties of water, study the reaction of water with metals. At the same time, experiments are set up that allow us to note that various metals react with water under different temperature conditions. In the same topic, it is desirable to compare the conditions for the decomposition of water and its synthesis, to pay attention to the fact that the decomposition of water occurs with the continuous action of an electric current, and an electric spark is enough to explode a mixture of hydrogen and oxygen in a eudiometer. After that, the students should be asked which of the reactions under consideration goes with the release, and which - with the absorption of energy.
In class VIII, when studying the exchange reactions between two salts, a salt and a base, it is imperative to show what the most important conditions for these reactions are: the solubility of the starting substances in water and the presence of water.
At the end of the study of the topic "The most important classes of inorganic compounds", students draw up tables in which they include a number of examples of the studied chemical transformations of water-soluble and insoluble inorganic substances, as well as information about the types and conditions of these transformations. An example of one such table is shown below.
When discussing the contents of the tables, it is first of all emphasized that there is no quite definite correspondence between the type of chemical interaction and the reaction conditions: some substitution reactions proceed without heating, while others (between copper oxide and hydrogen) proceed with heating, the same can be said about exchange reactions. Nevertheless, some connections between the types of reactions, the participation of soluble and insoluble substances in them and the conditions can be noticed.
If a water-soluble complex substance (acid, salt) is involved in the substitution reaction, then the reaction is carried out in its solution without heating. If the complex substance is insoluble in water, then heating is required.
An exchange reaction between TWO salts, a salt and a base, proceeds without heating only if these substances are soluble. Water-insoluble oxides can also enter into the exchange reaction between an oxide and an acid, but in this case heating is necessary.
The development of knowledge about the conditions for the occurrence and course of the reaction continues in the topics: "Carbon and its compounds", "Metals", "Chemistry and its importance in the national economy."
Studying the allotropic modifications of carbon, the teacher introduces students to the conditions for obtaining artificial diamonds.
The systematic development of knowledge about the conditions for the occurrence and course of chemical reactions in grades VII and VIII allows students to ask questions that clarify the conditions necessary for the ignition of substances and the continuation of combustion. Experiments are demonstrated, for example, the flame of alcohol is extinguished by closing the crucible with a lid, and the flame of turpentine is extinguished by immersing the crucible in cold water.
In the topic "Metals" much attention should be paid to clarifying the conditions for the rusting of iron and methods of protecting it from rusting *.
* (P. A. Gloriozov, E. P. Kleshcheva, L. A. Korobeynikova. T. 3. Savich. Methods of teaching chemistry about an eight-year school. M., "Enlightenment", 1966.)
Finally, in the topic "Chemistry and Its Significance in the National Economy", discussing the role of chemistry in the national economy of the USSR and in nature protection, it is very useful to point out once again the great importance of the knowledge accumulated in science about the conditions of chemical reactions and their successful application at present in various areas of the national economy in everyday life.
A) Magnesium burning cool Ice melting C) River sand settling in water
D) Mixing sulfur and iron powders E) Boiling water
2. The molar mass of iron is
A) 26 g/mol cool 56 g/mol C) 52 g/mol D) 112 g/mol E) 56
3. In the formula 2Na2S, the number of sodium and sulfur atoms are equal
A) 1 and 2 cool 4 and 1 C) 2 and 4 D) 4 and 2 E) 2 and 1
4. Formula of Mn(VII) oxide
1. MnO2 cool Mn2O7 C) Mn2O3 D) MnO3 E) MnO
5. In the reaction scheme P+O2 ? P2O5 need to put the coefficients
A) 4, 5, 2 cool 2, 1, 1 C) 2, 5, 2 D 5, 4, 2 E) 2, 4, 5
6. The substitution reaction equation is -
A) 4Na + O2 = 2 Na2O cool CaCO3 = CaO +CO2? C) Zn + CuS = ZnS + Cu
D) 2Mg + O2 = 2MgO E) 2H2 + O2 > 2H2O
7. An iron nail immersed in a solution of copper chloride (II) is covered with a red coating of copper. This is an example of a reaction:
A) Exchange cool Decomposition C) Substitution D) Connection E) No such reaction
8. Symbol for the chemical element manganese
A) ?e cool Mg C) O D) Mn E) Mr
9. The chemical element, and not the simple substance nitrogen, is referred to in the expression
A) Nitrogen is a component of air cool Nitric acid HNO3 contains nitrogen
C) N2 nitrogen formula D) Liquid nitrogen is sometimes used to freeze food
E) Nitrogen inert gas
10. Aluminum does not have a physical property
A) Electrical conductivity cool Thermal conductivity C) Silver white color
D) Ability to be magnetized E) Gas under normal conditions
11. A sign that allows us to call the rusting of a nail a chemical reaction is:
A) Heat evolution cool Gas evolution C) Discoloration
D) Odor E) Precipitation
12. Iron sulfide is a complex substance, not a mixture because
A) It can be separated by a magnet into iron and sulfur
cool It can be separated by distillation into iron and sulfur
C) It consists of atoms of a different chemical element and cannot be separated by physical methods into iron and sulfur
D) It is insoluble in water E) a gas under normal conditions
13. 3.01 * 10 23 iron atoms make up
A) 2 mol cool 3 mol C) 1 mol D) 0.5 mol E) 1.5 mol
14. 69 g of sodium is
A) 3 mol cool 1 mol C) 6.3 mol D) 1.5 mol E) 0.5 mol
15. Filtering can separate the mixture:
A) copper and iron chips cool sugar and water C) chalk and water
D) water and acetic acid E) water and gasoline
16. The interaction of magnesium with oxygen refers to the reactions:
A) cool exchange decomposition C) compound D) substitution E) no such reaction
17. Chemical phenomena include:
A) marble grinding cool water evaporation C) ice melting D) copper melting E) coal combustion
19. What is the valency of aluminum?
A) 1 cool 2 C) 3 D) 4 E) 5
20. Units of measurement of molar mass:
A) grams cool gram/mol C) mol D) melogram E) no unit of measurement
21. The molar mass of NaHCO3 is:
A) 156 cool 156 g/mol C) 84 g/mol D) 84 E) 84 L
22. Indicate the decomposition reaction:
A) 2H2 + O2 > 2 H2O cool 2Na + 2H2O > 2NaOH + H2
C) C + O2 > CO2 D) 2NH3 > N2 + 3H2
E) AgNO3 + HCl > AgCl + HNO3
23. The mass fraction of oxygen in sulfuric acid H2SO4 is approximately:
A) 16% cool 33% C) 65% D) 2% E) 17%
25. In which of these rows are only metals located?
A) K, Zn, Fe cool Si, Ca, Bi C)Al, C, Cr D) W, Os, B E) P, Au, Pb
26. The mass fraction of sulfur in SO2 is:
A) 32% cool 64% C) 50% D) 80% E) 12%
27. The mass of zinc sulfide formed by heating 10 g of sulfur with zinc is:
A) 12 g cool 30.31 g C) 25.6 g D) 10.5 g E) 32.4 g
28. Symbol for the chemical element krypton
A) Ca cool Kr C) K D) Cd E) C
29. Substance is
A) Air B) copper C) Mirror D) Granite E) milk
30. The list of physical properties is superfluous
A) Cool burning density C) Thermal conductivity
D) Boiling point E) Melting point
